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|May the source be with you, but remember the KISS principle ;-)
|Scripting in shell and Perl
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There are many people who use UNIX or Linux but who IMHO do not understand UNIX. UNIX is not just an operating system, it is a way of doing things, and the shell plays a key role by providing the glue that makes it work. The UNIX methodology relies heavily on reuse of a set of tools rather than on building monolithic applications. Even perl programmers often miss the point, writing the heart and soul of the application as perl script without making use of the UNIX toolkit.
David Korn(bold italic is mine -- BNN)
col A semi-forgotten tool to converting man pages to text
dos2unix - DOS to UNIX text converter
IMHO there are three Unix tools that can spell the difference between really good programmer or sysadmin and just above average one (even if the latter has solid knowledge of shell and Perl, knowledge of shell and Perl is necessary but not sufficient):
OFM (Midnight Commander, Deco, XNC) - a unique class of file managers that greatly accelirate working with the classic command line Unix tools. Paradoxically came to Unix from DOS. See The Orthodox File Manager(OFM) Paradigm. Chapter 4.
Expect - a unique Unix tool (that is now available for Windows too). BTW one of the earlier names for Expect was "sex" as it related to "intercourse" of programs ;-). I strongly recommend to learn how to use it. See TCL, TK & Expect for more information
TCL -- Tool command language. This is a unique language that permits automating tasks that neither shell not Perl can do. It is used in Expect (see above). Unfortunately politics of Unix (forking efforts of Richard Stallman (see Guile, a Scheme-based GNU macro language :-( ) and, especially, Sun fascination with Java) prevented TCL from becoming a standard Unix macro language. As Wikipedia noted " Despite the enthusiasm of its users and developers, many novice programmers find Scheme intimidating - and the average skill level of scripting language programmers is substantially lower than for system and application programmers. Hence Guile, despite its many benefits, struggles for mainstream acceptance in the Linux/Unix world. ". For the dark side of RMS see The Tcl War and the second part of my RMS biography
This two tools can also be used as a fine text in interviews on advanced Unix-related positions if you have several similar candidates. Other things equal, their knowledge definitely demonstrate the level of Unix culture superior to the average "command line junkies" level ;-)
Overview of books about GNU/open source tools can be found in Unix tools bibliography. There not that much good books on the subject, still even average books can provide you with insight in usage of the tool that you might never get via daily practice.
Please note that Unix is a pretty complex system and some aspects of it are non-obvious even for those who have more than ten years of experience.
Dr. Nikolai Bezroukov
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Oct 22, 2017 | seismo.berkeley.edu
A tr script to remove all non-printing characters from a file is below. Non-printing characters may be invisible, but cause problems with printing or sending the file via electronic mail. You run it from Unix command prompt, everything on one line:> tr -d '\001'-'\011''\013''\014''\016'-'\037''\200'-'\377' < filein > fileoutWhat is the meaning of this tr script is, that it deletes all charactes with octal value from 001 to 011, characters 013, 014, characters from 016 to 037 and characters from 200 to 377. Other characters are copied over from filein to fileout and these are printable. Please remember, you can not fold a line containing tr command, everything must be on one line, how long it would be. In practice, this script solves some mysterious Unix printing problems.
Type in a text file named "f127.TR" with the line starting tr above. Print the file on screen with cat f127.TR command, replace "filein" and "fileout" with your file names, not same the file, then copy and paste the line and run (execute) it. Please, remember this does not solve Unix end-of-file problem, that is the character '\000', also known as a 'null', in the file. Nor does it handle binary file problem, that is a file starting with two zeroes '\060' and '\060'
Sometimes there are some invisible characters causing havoc. This tr command line converts tabulate- characters into hashes (#) and formfeed- characters into stars (*).> tr '\011\014' '#*' < filein > fileoutThe numeric value of tabulate is 9, hex 09, octal 011 and in C-notation it is \t or \011. Formfeed is 12, hex 0C, octal 014 and in C-notation it is \f or \014. Please note, tr replaces character from the first (leftmost) group with corresponding character in the second group. Characters in octal format, like \014 are counted as one character each.
Oct 01, 2017 | linoxide.com
How to Use "Script" Command To Record Linux Terminal Session May 30, 2014 By Pungki Arianto Updated June 14, 2017 Facebook Google+ Twitter Pinterest LinkedIn StumbleUpon Reddit Email This script command is very helpful for system admin. If any problem occurs to the system, it is very difficult to find what command was executed previously. Hence, system admin knows the importance of this script command. Sometimes you are on the server and you think to yourself that your team or somebody you know is actually missing a documentation on how to do a specific configuration. It is possible for you to do the configuration, record all actions of your shell session and show the record to the person who will see exactly what you had (the same output) on your shell at the moment of the configuration. How does script command work?
script command records a shell session for you so that you can look at the output that you saw at the time and you can even record with timing so that you can have a real-time playback. It is really useful and comes in handy in the strangest kind of times and places.
The script command keeps action log for various tasks. The script records everything in a session such as things you type, things you see. To do this you just type script command on the terminal and type exit when finished. Everything between the script and the exit command is logged to the file. This includes the confirmation messages from script itself.1. Record your terminal session
script makes a typescript of everything printed on your terminal. If the argument file is given, script saves all dialogue in the indicated file in the current directory. If no file name is given, the typescript is saved in default file typescript. To record your shell session so what you are doing in the current shell, just use the command below# script shell_record1 Script started, file is shell_record1
It indicates that a file shell_record1 is created. Let's check the file# ls -l shell_* -rw-r--r-- 1 root root 0 Jun 9 17:50 shell_record1
After completion of your task, you can enter exit or
Ctrl-dto close down the script session and save the file.# exit exit Script done, file is shell_record1
You can see that script indicates the filename.2. Check the content of a recorded terminal session
When you use script command, it records everything in a session such as things you type so all your output. As the output is saved into a file, it is possible after to check its content after existing a recorded session. You can simply use a text editor command or a text file command viewer.# cat shell_record1 Script started on Fri 09 Jun 2017 06:23:41 PM UTC [root@centos-01 ~]# date Fri Jun 9 18:23:46 UTC 2017 [root@centos-01 ~]# uname -a Linux centos-01 3.10.0-514.16.1.el7.x86_64 #1 SMP Wed Apr 12 15:04:24 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux [root@centos-01 ~]# whoami root [root@centos-01 ~]# pwd /root [root@centos-01 ~]# exit exit Script done on Fri 09 Jun 2017 06:25:11 PM UTC
While you view the file you realize that the script also stores line feeds and backspaces. It also indicates the time of the recording to the top and the end of the file.3. Record several terminal session
You can record several terminal session as you want. When you finish a record, just begin another new session record. It can be helpful if you want to record several configurations that you are doing to show it to your team or students for example. You just need to name each recording file.
For example, let us assume that you have to do OpenLDAP , DNS , Machma configurations. You will need to record each configuration. To do this, just create recording file corresponding to each configuration when finished.# script openldap_record ............... configuration step .............. # exit
When you have finished with the first configuration, begin to record the next configuration# script machma_record ............ configuration steps ............. # exit
And so on for the other. Note that if you script command followed by existing filename, the file will be replaced. So you will lost everything.
Now, let us imagine that you have begun Machma configuration but you have to abort its configuration in order to finish DNS configuration because of some emergency case. Now you want to continue the machma configuration where you left. It means you want to record the next steps into the existing file machma_record without deleting its previous content; to do this you will use
script -acommand to append the new output to the file.
This is the content of our recorded file
Now if we want to continue our recording in this file without deleting the content already present, we will do# script -a machma_record Script started, file is machma_record
Now continue the configuration, then exit when finished and let's check the content of the recorded file.
Note the new time of the new record which appears. You can see that the file has the previous and actual records.4. Replay a linux terminal session
We have seen that it is possible to see the content of the recorded file with commands to display a text file content. The script command also gives the possibility to see the recorded session as a video. It means that you will review exactly what you have done step by step at the moment you were entering the commands as if you were looking a video. So you will playback/replay the recorded terminal session.
To do it, you have to use
--timingoption of script command when you will start the record.# script --timing=file_time shell_record1 Script started, file is shell_record1
See that the file into which to record is shell_record1. When the record is finished, exit normally# exit exit Script done, file is shell_record1
Let's see check the content of file_time# cat file_time 0.807440 49 0.030061 1 116.131648 1 0.226914 1 0.033997 1 0.116936 1 0.104201 1 0.392766 1 0.301079 1 0.112105 2 0.363375 152
--timingoption outputs timing data to the file indicated. This data contains two fields, separated by a space which indicates how much time elapsed since the previous output how many characters were output this time. This information can be used to replay typescripts with realistic typing and output delays.
Now to replay the terminal session, we use scriptreplay command instead of script command with the same syntax when recording the session. Look below# scriptreplay --timing=file_time shell_record1
You will that the recorded session with be played as if you were looking a video which was recording all that you were doing. You can just insert the timing file without indicating all the --timing=file_time. Look below# scriptreplay file_time shell_record1
So you understand that the first parameter is the timing file and the second is the recorded file.Conclusion
The script command can be your to-go tool for documenting your work and showing others what you did in a session. It can be used as a way to log what you are doing in a shell session. When you run script, a new shell is forked. It reads standard input and output for your terminal tty and stores the data in a file.
Aug 28, 2017 | serverfault.com
I have one older ubuntu server, and one newer debian server and I am migrating data from the old one to the new one. I want to use rsync to transfer data across to make final migration easier and quicker than the equivalent tar/scp/untar process.
As an example, I want to sync the home folders one at a time to the new server. This requires root access at both ends as not all files at the source side are world readable and the destination has to be written with correct permissions into /home. I can't figure out how to give rsync root access on both sides.
I've seen a few related questions, but none quite match what I'm trying to do.
I have sudo set up and working on both servers. ubuntu ssh debian rsync root
share improve this question asked Apr 28 '10 at 9:18 Tim Abell 732 20
add a comment | 3 Answers active oldest votes
up vote down vote accepted Actually you do NOT need to allow root authentication via SSH to run rsync as Antoine suggests. The transport and system authentication can be done entirely over user accounts as long as you can run rsync with sudo on both ends for reading and writing the files.
As a user on your destination server you can suck the data from your source server like this:sudo rsync -aPe ssh --rsync-path='sudo rsync' boron:/home/fred /home/
The user you run as on both servers will need passwordless* sudo access to the rsync binary, but you do NOT need to enable ssh login as root anywhere. If the user you are using doesn't match on the other end, you can add user@boron: to specify a different remote user.
Good luck.
*or you will need to have entered the password manually inside the timeout window.
share improve this answer edited Jun 30 '10 at 13:51 answered Apr 28 '10 at 22:06 Caleb 9,089 27 43
add a comment |
1 Although this is an old question I'd like to add word of CAUTION to this accepted answer. From my understanding allowing passwordless "sudo rsync" is equivalent to open the root account to remote login. This is because with this it is very easy to gain full root access, e.g. because all system files can be downloaded, modified and replaced without a password. Ascurion Jan 8 '16 at 16:30
up vote down vote If your data is not highly sensitive, you could use tar and socat. In my experience this is often faster as rsync over ssh.
You need socat or netcat on both sides.
On the target host, go to the directory where you would like to put your data, after that run: socat TCP-LISTEN:4444 - | tar xzf -
If the target host is listening, start it on the source like: tar czf - /home/fred /home/ | socat - TCP:ip-of-remote-server:4444
For this setup you'll need a reliably connection between the 2 servers.
share improve this answer answered Apr 28 '10 at 21:20 Jeroen Moors
add a comment |
Good point. In a trusted environment, you'll pick up a lot of speed by not encrypting. It might not matter on small files, but with GBs of data it will. pboin May 18 '10 at 10:53
up vote down vote Ok, i've pieced together all the clues to get something that works for me.
Lets call the servers "src" & "dst".
Set up a key pair for root on the destination server, and copy the public key to the source server:dest $ sudo -i dest # ssh-keygen dest # exit dest $ scp /root/id_rsa.pub src:
Add the public key to root's authorized keys on the source serversrc $ sudo -i src # cp /home/tim/id_rsa.pub .ssh/authorized_keys
Back on the destination server, pull the data across with rsync:dest $ sudo -i dest # rsync -aP src:/home/fred /home/
Feb 06, 2014 | www.cyberciti.bizNovember 9, 2012 February 6, 2014 in Categories Commands , File system , Linux , UNIX last updated February 6, 2014
How do I use the rsync tool to copy only the hidden files and directory (such as ~/.ssh/, ~/.foo, and so on) from /home/jobs directory to the /mnt/usb directory under Unix like operating system?
The rsync program is used for synchronizing files over a network or local disks. To view or display only hidden files with ls command:
ls -ld ~/.??*
ls -ld ~/.[^.]*
Sample outputs:
rsync not synchronizing all hidden .dot files?
Fig:01 ls command to view only hidden files
In this example, you used the pattern .[^.]* or .??* to select and display only hidden files using ls command . You can use the same pattern with any Unix command including rsync command. The syntax is as follows to copy hidden files with rsync:
rsync -av /path/to/dir/.??* /path/to/dest rsync -avzP /path/to/dir/.??* /mnt/usb rsync -avzP $HOME/.??* firstname.lastname@example.com:/path/to/backup/users/u/user1 rsync -avzP ~/.[^.]* email@example.com:/path/to/backup/users/u/user1
rsync -av /path/to/dir/.??* /path/to/dest rsync -avzP /path/to/dir/.??* /mnt/usb rsync -avzP $HOME/.??* email@example.com:/path/to/backup/users/u/user1 rsync -avzP ~/.[^.]* firstname.lastname@example.com:/path/to/backup/users/u/user1
In this example, copy all hidden files from my home directory to /mnt/test:
rsync -avzP ~/.[^.]* /mnt/test
rsync -avzP ~/.[^.]* /mnt/test
Sample outputs:
Vivek Gite is the creator of nixCraft and a seasoned sysadmin and a trainer for the Linux operating system/Unix shell scripting. He has worked with global clients and in various industries, including IT, education, defense and space research, and the nonprofit sector. Follow him on Twitter , Facebook , Google+ .
Fig.02 Rsync example to copy only hidden files
Aug 28, 2017 | superuser.com
1 Answer active oldest votes
up vote down vote favorite Trying to copy files with rsync, it complains:rsync: send_files failed to open "VirtualBox/Machines/Lubuntu/Lubuntu.vdi" \ (in media): Permission denied (13)
That file is not copied. Indeed the file permissions of that file are very restrictive on the server side:-rw------- 1 1000 1000 3133181952 Nov 1 2011 Lubuntu.vdi
I call rsync withsudo rsync -av --fake-super root@sheldon::media /mnt/media
The rsync daemon runs as root on the server. root can copy that file (of course). rsyncd has "fake super = yes" set in /etc/rsyncd.conf.
What can I do so that the file is copied without changing the permissions of the file on the server? rsync file-permissions
share improve this question asked Dec 29 '12 at 10:15 Torsten Bronger 207
add a comment |
If you use RSync as daemon on destination, please post
grep rsync /var/log/daemonto improve your question – F. Hauri Dec 29 '12 at 13:23
up vote down vote As you appear to have root access to both servers have you tried a: --force ?
Alternatively you could bypass the rsync daemon and try a direct sync e.g.rsync -optg --rsh=/usr/bin/ssh --rsync-path=/usr/bin/rsync --verbose --recursive --delete-after --force root@sheldon::media /mnt/media
share improve this answer edited Jan 2 '13 at 10:55 answered Dec 29 '12 at 13:21 arober11 376
Using ssh means encryption, which makes things slower. --force does only affect directories, if I read the man page correctly. – Torsten Bronger Jan 1 '13 at 23:08
Unless your using ancient kit, the CPU overhead of encrypting / decrypting the traffic shouldn't be noticeable, but you will loose 10-20% of your bandwidth, through the encapsulation process. Then again 80% of a working link is better than 100% of a non working one :) – arober11 Jan 2 '13 at 10:52
do have an "ancient kit". ;-) (Slow ARM CPU on a NAS.) But I now mount the NAS with NFS and use rsync (with "sudo") locally. This solves the problem (and is even faster). However, I still think that my original problem must be solvable using the rsync protocol (remote, no ssh). – Torsten Bronger Jan 4 '13 at 7:55
Aug 28, 2017 | unix.stackexchange.com
up vote down vote favorite
nixnotwin , asked Sep 21 '12 at 5:11On my Ubuntu server there are about 150 shell accounts. All usernames begin with the prefix u12.. I have root access and I am trying to copy a directory named "somefiles" to all the home directories. After copying the directory the user and group ownership of the directory should be changed to user's. Username, group and home-dir name are same. How can this be done?
Gilles , answered Sep 21 '12 at 23:44Do the copying as the target user. This will automatically make the target files. Make sure that the original files are world-readable (or at least readable by all the target users). Run
chmodafterwards if you don't want the copied files to be world-readable.getent passwd | awk -F : '$1 ~ /^u12/ {print $1}' | while IFS= read -r user; do su "$user" -c 'cp -Rp /original/location/somefiles ~/' done
Aug 28, 2017 | stackoverflow.comup vote 10 down vote favorite 4
jeffery_the_wind , asked Mar 6 '12 at 15:36I am using rsync to replicate a web folder structure from a local server to a remote server. Both servers are ubuntu linux. I use the following command, and it works well:rsync -az /var/www/ email@example.com:/var/www/
The usernames for the local system and the remote system are different. From what I have read it may not be possible to preserve all file and folder owners and groups. That is OK, but I would like to preserve owners and groups just for the www-data user, which does exist on both servers.
Is this possible? If so, how would I go about doing that?
There is some mention of rsync being able to preserve ownership and groups on remote file syncs here: http://lists.samba.org/archive/rsync/2005-August/013203.html
I ended up getting the desired affect thanks to many of the helpful comments and answers here. Assuming the IP of the source machine is 10.1.1.2 and the IP of the destination machine is 10.1.1.1. I can use this line from the destination machine:sudo rsync -az email@example.com:/var/www/ /var/www/
This preserves the ownership and groups of the files that have a common user name, like www-data. Note that using
sudodoes not preserve these permissions.
ghoti , answered Mar 6 '12 at 19:01You can also sudo the rsync on the target host by using the
--rsync-pathoption:# rsync -av --rsync-path="sudo rsync" /path/to/files user@targethost:/path
This lets you authenticate as
useron targethost, but still get privileged write permission through
sudo. You'll have to modify your sudoers file on the target host to avoid sudo's request for your password.
man sudoersor run
sudo visudofor instructions and samples.
You mention that you'd like to retain the ownership of files owned by www-data, but not other files. If this is really true, then you may be out of luck unless you implement
chownor a second run of
rsyncto update permissions. There is no way to tell rsync to preserve ownership for just one user .
That said, you should read about rsync's
--files-fromoption.rsync -av /path/to/files user@targethost:/path find /path/to/files -user www-data -print | \ rsync -av --files-from=- --rsync-path="sudo rsync" /path/to/files user@targethost:/path
I haven't tested this, so I'm not sure exactly how piping find's output into
--files-from=-will work. You'll undoubtedly need to experiment.
xato , answered Mar 6 '12 at 15:39As far as I know, you cannot
chownfiles to somebody else than you, if you are not root. So you would have to
rsyncusing the
www-dataaccount, as all files will be created with the specified user as owner. So you need to
chownthe files afterwards.
user2485267 , answered Jun 14 '13 at 8:22I had a similar problem and cheated the rsync command,
rsync -avz --delete firstname.lastname@example.com:/home//domains/site/public_html/ /home/domains2/public_html && chown -R wwwusr:wwwgrp /home/domains2/public_html/
the && runs the chown against the folder when the rsync completes successfully (1x '&' would run the chown regardless of the rsync completion status)
Graham , answered Mar 6 '12 at 15:51
The root users for the local system and the remote system are different.
What does this mean? The root user is uid 0. How are they different?
Any user with read permission to the directories you want to copy can determine what usernames own what files. Only root can change the ownership of files being written .
You're currently running the command on the source machine, which restricts your writes to the permissions associated with email@example.com. Instead, you can try to run the command as root on the target machine. Your read access on the source machine isn't an issue.
So on the target machine (10.1.1.1), assuming the source is 10.1.1.2:# rsync -az firstname.lastname@example.com:/var/www/ /var/www/
Make sure your groups match on both machines.
Also, set up access to email@example.com using a DSA or RSA key, so that you can avoid having passwords floating around. For example, as root on your target machine, run:# ssh-keygen -d
Then take the contents of the file
/root/.ssh/id_dsa.puband add it to
~user/.ssh/authorized_keyson the source machine. You can
ssh firstname.lastname@example.com root from the target machine to see if it works. If you get a password prompt, check your error log to see why the key isn't working.
ghoti , answered Mar 6 '12 at 18:54Well, you could skip the challenges of rsync altogether, and just do this through a tar tunnel.sudo tar zcf - /path/to/files | \ ssh user@remotehost "cd /some/path; sudo tar zxf -"
You'll need to set up your SSH keys as Graham described.
Note that this handles full directory copies, not incremental updates like rsync.
The idea here is that:
- you tar up your directory,
- instead of creating a tar file, you send the tar output to stdout,
- that stdout is piped through an SSH command to a receiving tar on the other host,
- but that receiving tar is run by sudo, so it has privileged write access to set usernames.
Aug 28, 2017 | superuser.com
1 Answer active oldest votes
up vote down vote favorite I'm trying to use rsync to copy a set of files from one system to another. I'm running the command as a normal user (not root). On the remote system, the files are owned by apache and when copied they are obviously owned by the local account (fred).
My problem is that every time I run the rsync command, all files are re-synched even though they haven't changed. I think the issue is that rsync sees the file owners are different and my local user doesn't have the ability to change ownership to apache, but I'm not including the
-ooptions so I thought this would not be checked. If I run the command as root, the files come over owned by apache and do not come a second time if I run the command again. However I can't run this as root for other reasons. Here is the command:/usr/bin/rsync --recursive --rsh=/usr/bin/ssh --rsync-path=/usr/bin/rsync --verbose firstname.lastname@example.com:/src/dir/ /local/dirunix rsync
share improve this question edited May 2 '11 at 23:53 Gareth 13.9k 11 44 58 asked May 2 '11 at 23:43 Fred Snertz 11
add a comment |
Why can't you run rsync as root? On the remote system, does fred have read access to the apache-owned files? – chrishiestand May 3 '11 at 0:32
Ah, I left out the fact that there are ssh keys set up so that local fred can become remote root, so yes fred/root can read them. I know this is a bit convoluted but its real. – Fred Snertz May 3 '11 at 14:50
Always be careful when root can ssh into the machine. But if you have password and challenge response authentication disabled it's not as bad. – chrishiestand May 3 '11 at 17:32
up vote down vote Here's the answer to your problem:-c, --checksum This changes the way rsync checks if the files have been changed and are in need of a transfer. Without this option, rsync uses a "quick check" that (by default) checks if each file's size and time of last modification match between the sender and receiver. This option changes this to compare a 128-bit checksum for each file that has a matching size. Generating the checksums means that both sides will expend a lot of disk I/O reading all the data in the files in the transfer (and this is prior to any reading that will be done to transfer changed files), so this can slow things down significantly. The sending side generates its checksums while it is doing the file-system scan that builds the list of the available files. The receiver generates its checksums when it is scanning for changed files, and will checksum any file that has the same size as the corresponding sender's file: files with either a changed size or a changed checksum are selected for transfer. Note that rsync always verifies that each transferred file was correctly reconstructed on the receiving side by checking a whole-file checksum that is generated as the file is transferred, but that automatic after-the-transfer verification has nothing to do with this option's before-the-transfer "Does this file need to be updated?" check. For protocol 30 and beyond (first supported in 3.0.0), the checksum used is MD5. For older protocols, the checksum used is MD4.
So run:/usr/bin/rsync -c --recursive --rsh=/usr/bin/ssh --rsync-path=/usr/bin/rsync --verbose email@example.com:/src/dir/ /local/dir
Note there may be a time+disk churn tradeoff by using this option. Personally, I'd probably just sync the file's mtimes too:/usr/bin/rsync -t --recursive --rsh=/usr/bin/ssh --rsync-path=/usr/bin/rsync --verbose email@example.com:/src/dir/ /local/dir
share improve this answer edited May 3 '11 at 17:55 answered May 3 '11 at 17:48 chrishiestand 1,098 10
Awesome. Thank you. Looks like the second option is going to work for me and I found the first very interesting. – Fred Snertz May 3 '11 at 18:40
psst, hit the green checkbox to give my answer credit ;-) Thx. – chrishiestand May 12 '11 at 1:56
Aug 28, 2017 | unix.stackexchange.com
up vote 11 down vote favorite 1
Eugene Yarmash , asked Apr 24 '13 at 16:35I have a bash script which uses
rsyncto backup files in Archlinux. I noticed that
rsyncfailed to copy a file from
/sys, while
cpworked just fine:# rsync /sys/class/net/enp3s1/address /tmp rsync: read errors mapping "/sys/class/net/enp3s1/address": No data available (61) rsync: read errors mapping "/sys/class/net/enp3s1/address": No data available (61) ERROR: address failed verification -- update discarded. rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1052) [sender=3.0.9] # cp /sys/class/net/enp3s1/address /tmp ## this works
I wonder why does
rsyncfail, and is it possible to copy the file with it?
mattdm , answered Apr 24 '13 at 18:20Rsync has code which specifically checks if a file is truncated during read and gives this error !
ENODATA. I don't know why the files in
/syshave this behavior, but since they're not real files, I guess it's not too surprising. There doesn't seem to be a way to tell rsync to skip this particular check.
I think you're probably better off not rsyncing
/sysand using specific scripts to cherry-pick out the particular information you want (like the network card address).
Runium , answered Apr 25 '13 at 0:23First off
/sysis a pseudo file system . If you look at
/proc/filesystemsyou will find a list of registered file systems where quite a few has
nodevin front. This indicates they are pseudo filesystems . This means they exists on a running kernel as a RAM-based filesystem. Further they do not require a block device.$ cat /proc/filesystems nodev sysfs nodev rootfs nodev bdev ...
At boot the kernel mount this system and updates entries when suited. E.g. when new hardware is found during boot or by
/etc/mtabyou typically find the mount by:sysfs /sys sysfs rw,noexec,nosuid,nodev 0 0
For a nice paper on the subject read Patric Mochel's – The sysfs Filesystem .
stat of /sys files
If you go into a directory under
/sysand do a
ls -lyou will notice that all files has one size. Typically 4096 bytes. This is reported by
sysfs.:/sys/devices/pci0000:00/0000:00:19.0/net/eth2$ ls -l -r--r--r-- 1 root root 4096 Apr 24 20:09 addr_assign_type -r--r--r-- 1 root root 4096 Apr 24 20:09 address -r--r--r-- 1 root root 4096 Apr 24 20:09 addr_len ...
Further you can do arsync vs. cp
staton a file and notice another distinct feature; it occupies 0 blocks. Also inode of root (stat /sys) is 1.
/stat/fstypically has inode 2. etc.
The easiest explanation for rsync failure of synchronizing pseudo files is perhaps by example.
Say we have a file named
addressthat is 18 bytes. An
statof the file reports 4096 bytes.
- Opens file descriptor, fd.
- Uses fstat(fd) to get information such as size.
- Set out to read size bytes, i.e. 4096. That would be line 253 of the code linked by @mattdm .
read_size == 4096
- Ask; read: 4096 bytes.
- A short string is read i.e. 18 bytes.
nread == 18
read_size = read_size - nread (4096 - 18 = 4078)
- Ask; read: 4078 bytes
- 0 bytes read (as first read consumed all bytes in file).
nread == 0, line 255
- Unable to read
4096bytes. Zero out buffer.
- Set error
- Return.
- Report error.
- Retry. (Above loop).
- Fail.
- Report error.
During this process it actually reads the entire file. But with no size available it cannot validate the result – thus failure is only option.cp
- Opens file descriptor, fd.
- Uses fstat(fd) to get information such as st_size (also uses lstat and stat).
- Check if file is likely to be sparse. That is the file has holes etc.copy.c:1010 /* Use a heuristic to determine whether SRC_NAME contains any sparse * blocks. If the file has fewer blocks than would normally be * needed for a file of its size, then at least one of the blocks in * the file is a hole. */ sparse_src = is_probably_sparse (&src_open_sb);
statreports file to have zero blocks it is categorized as sparse.
- Tries to read file by extent-copy (a more efficient way to copy normal sparse files), and fails.
- Copy by sparse-copy.
- Starts out with max read size of MAXINT.
18446744073709551615bytes on a 32 bit system.
- Ask; read 4096 bytes. (Buffer size allocated in memory from stat information.)
- A short string is read i.e. 18 bytes.
- Check if a hole is needed, nope.
- Write buffer to target.
- Subtract 18 from max read size.
- Ask; read 4096 bytes.
- 0 bytes as all got consumed in first read.
- Return success.
- All OK. Update flags for file.
,Might be related, but extended attribute calls will fail on sysfs:
[root@hypervisor eth0]# lsattr address
lsattr: Inappropriate ioctl for device While reading flags on address
[root@hypervisor eth0]#
Looking at my strace it looks like rsync tries to pull in extended attributes by default:
22964 <... getxattr resumed> , 0x7fff42845110, 132) = -1 ENODATA (No data available)
I tried finding a flag to give rsync to see if skipping extended attributes resolves the issue but wasn't able to find anything (
--xattrsturns them on at the destination).
Aug 28, 2017 | ubuntuforums.org
View Full Version : [ubuntu] Rsync doesn't copy everyting
Scormen May 31st, 2009, 10:09 AM Hi all,
I'm having some trouble with rsync. I'm trying to sync my local /etc directory to a remote server, but this won't work.
The problem is that it seems he doesn't copy all the files.
The local /etc dir contains 15MB of data, after a rsync, the remote backup contains only 4.6MB of data.
Rsync is running by root. I'm using this command:
rsync --rsync-path="sudo rsync" -e "ssh -i /root/.ssh/backup" -avz --delete --delete-excluded -h --stats /etc email@example.com:/home/kris/backup/laptopkris
I hope someone can help.
Scormen May 31st, 2009, 11:05 AM I found that if I do a local sync, everything goes fine.
But if I do a remote sync, it copies only 4.6MB.
Any idea?
LoneWolfJack May 31st, 2009, 05:14 PM never used rsync on a remote machine, but "sudo rsync" looks wrong. you probably can't call sudo like that so the ssh connection needs to have the proper privileges for executing rsync.
just an educated guess, though.
Scormen May 31st, 2009, 05:24 PM Thanks for your answer.
In /etc/sudoers I have added next line, so "sudo rsync" will work.
kris ALL=NOPASSWD: /usr/bin/rsync
I also tried without --rsync-path="sudo rsync", but without success.
I have also tried on the server to pull the files from the laptop, but that doesn't work either.
LoneWolfJack May 31st, 2009, 05:30 PM in the rsync help file it says that --rsync-path is for the path to rsync on the remote machine, so my guess is that you can't use sudo there as it will be interpreted as a path.
so you will have to do --rsync-path="/path/to/rsync" and make sure the ssh login has root privileges if you need them to access the files you want to sync.
--rsync-path="sudo rsync" probably fails because
a) sudo is interpreted as a path
b) the space isn't escaped
c) sudo probably won't allow itself to be called remotely
again, this is not more than an educated guess.
Scormen May 31st, 2009, 05:45 PM I understand what you mean, so I tried also:
rsync -Cavuhzb --rsync-path="/usr/bin/rsync" -e "ssh -i /root/.ssh/backup" /etc email@example.com:/home/kris/backup/laptopkris
Then I get this error:
sending incremental file list
rsync: recv_generator: failed to stat "/home/kris/backup/laptopkris/etc/chatscripts/pap": Permission denied (13)
rsync: recv_generator: failed to stat "/home/kris/backup/laptopkris/etc/chatscripts/provider": Permission denied (13)
rsync: symlink "/home/kris/backup/laptopkris/etc/cups/ssl/server.crt" -> "/etc/ssl/certs/ssl-cert-snakeoil.pem" failed: Permission denied (13)
rsync: symlink "/home/kris/backup/laptopkris/etc/cups/ssl/server.key" -> "/etc/ssl/private/ssl-cert-snakeoil.key" failed: Permission denied (13)
rsync: recv_generator: failed to stat "/home/kris/backup/laptopkris/etc/ppp/peers/provider": Permission denied (13)
rsync: recv_generator: failed to stat "/home/kris/backup/laptopkris/etc/ssl/private/ssl-cert-snakeoil.key": Permission denied (13)
sent 86.85K bytes received 306 bytes 174.31K bytes/sec
total size is 8.71M speedup is 99.97
rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1058) [sender=3.0.5]
And the same command with "root" instead of "kris".
Then, I get no errors, but I still don't have all the files synced.
Scormen June 1st, 2009, 09:00 AM Sorry for this bump.
I'm still having the same problem.
Any idea?
binary10 June 1st, 2009, 10:36 AM I understand what you mean, so I tried also:
rsync -Cavuhzb --rsync-path="/usr/bin/rsync" -e "ssh -i /root/.ssh/backup" /etc firstname.lastname@example.com:/home/kris/backup/laptopkris
Then I get this error:
And the same command with "root" instead of "kris".
Then, I get no errors, but I still don't have all the files synced.
Maybe there's a nicer way but you could place /usr/bin/rsync into a private protected area and set the owner to root place the sticky bit on it and change your rsync-path argument such like:
# on the remote side, aka email@example.com
mkdir priv-area
# protect it from normal users running a priv version of rsync
chmod 700 priv-area
cd priv-area
cp -p /usr/local/bin/rsync ./rsync-priv
sudo chown 0:0 ./rsync-priv
sudo chmod +s ./rsync-priv
ls -ltra # rsync-priv should now be 'bold-red' in bash
Looking at your flags, you've specified a cvs ignore factor, ignore files that are updated on the target, and you're specifying a backup of removed files.
rsync -Cavuhzb --rsync-path="/home/kris/priv-area/rsync-priv" -e "ssh -i /root/.ssh/backup" /etc firstname.lastname@example.com:/home/kris/backup/laptopkris
From those qualifiers you're not going to be getting everything sync'd. It's doing what you're telling it to do.
If you really wanted to perform a like for like backup.. (not keeping stuff that's been changed/deleted from the source. I'd go for something like the following.
rsync --archive --delete --hard-links --one-file-system --acls --xattrs --dry-run -i --rsync-path="/home/kris/priv-area/rsync-priv" --rsh="ssh -i /root/.ssh/backup" /etc/ firstname.lastname@example.com:/home/kris/backup/laptopkris/etc/
Remove the --dry-run and -i when you're happy with the output, and it should do what you want. A word of warning, I get a bit nervous when not seeing trailing (/) on directories as it could lead to all sorts of funnies if you end up using rsync on softlinks.
Scormen June 1st, 2009, 12:19 PM Thanks for your help, binary10.
I've tried what you have said, but still, I only receive 4.6MB on the remote server.
Thanks for the warning, I'll not that!
Did someone already tried to rsync their own /etc to a remote system? Just to know if this strange thing only happens to me...
binary10 June 1st, 2009, 01:22 PM Thanks for your help, binary10.
I've tried what you have said, but still, I only receive 4.6MB on the remote server.
Thanks for the warning, I'll not that!
Did someone already tried to rsync their own /etc to a remote system? Just to know if this strange thing only happens to me...
Ok so I've gone back and looked at your original post, how are you calculating 15MB of data under etc - via a du -hsx /etc/ ??
I do daily drive to drive backup copies via rsync and drive to network copies.. and have used them recently for restoring.
Sure my du -hsx /etc/ reports 17MB of data of which 10MB gets transferred via an rsync. My backup drives still operate.
rsync 3.0.6 has some fixes to do with ACLs and special devices rsyncing between solaris. but I think 3.0.5 is still ok with ubuntu to ubuntu systems.
Here is my test doing exactly what you you're probably trying to do. I even check the remote end..
binary10@jsecx25:~/bin-priv$ ./rsync --archive --delete --hard-links --one-file-system --stats --acls --xattrs --human-readable --rsync-path="~/bin/rsync-priv-os-specific" --rsh="ssh" /etc/ firstname.lastname@example.com:/home/kris/backup/laptopkris/etc/
Number of files: 3121
Number of files transferred: 1812
Total file size: 10.04M bytes
Total transferred file size: 10.00M bytes
Literal data: 10.00M bytes
Matched data: 0 bytes
File list size: 109.26K
File list generation time: 0.002 seconds
File list transfer time: 0.000 seconds
Total bytes sent: 10.20M
Total bytes received: 38.70K
sent 10.20M bytes received 38.70K bytes 4.09M bytes/sec
total size is 10.04M speedup is 0.98
binary10@jsecx25:~/bin-priv$ sudo du -hsx /etc/
17M /etc/
And then on the remote system I do the du -hsx
binary10@lenovo-n200:/home/kris/backup/laptopkris/etc$ cd ..
binary10@lenovo-n200:/home/kris/backup/laptopkris$ sudo du -hsx etc
17M etc
Scormen June 1st, 2009, 01:35 PM ow are you calculating 15MB of data under etc - via a du -hsx /etc/ ??
Indeed, on my laptop I see:
root@laptopkris:/home/kris# du -sh /etc/
15M /etc/
If I do the same thing after a fresh sync to the server, I see:
root@server:/home/kris# du -sh /home/kris/backup/laptopkris/etc/
4.6M /home/kris/backup/laptopkris/etc/
On both sides, I have installed Ubuntu 9.04, with version 3.0.5 of rsync.
So strange...
binary10 June 1st, 2009, 01:45 PM it does seem a bit odd.
I'd start doing a few diffs from the outputs find etc/ -printf "%f %s %p %Y\n" | sort
And see what type of files are missing.
- edit - Added the %Y file type.
Scormen June 1st, 2009, 01:58 PM Hmm, it's going stranger.
Now I see that I have all my files on the server, but they don't have their full size (bytes).
I have uploaded the files, so you can look into them.
Laptop: http://www.linuxontdekt.be/files/laptop.files
Server: http://www.linuxontdekt.be/files/server.files
binary10 June 1st, 2009, 02:16 PM If you look at the files that are different aka the ssl's they are links to local files else where aka linked to /usr and not within /etc/
aka they are different on your laptop and the server
Scormen June 1st, 2009, 02:25 PM I understand that soft links are just copied, and not the "full file".
But, you have run the same command to test, a few posts ago.
How is it possible that you can see the full 15MB?
binary10 June 1st, 2009, 02:34 PM I was starting to think that this was a bug with du.
The de-referencing is a bit topsy.
If you rsync copy the remote backup back to a new location back onto the laptop and do the du command. I wonder if you'll end up with 15MB again.
Scormen June 1st, 2009, 03:20 PM Good tip.
On the server side, the backup of the /etc was still 4.6MB.
I have rsynced it back to the laptop, to a new directory.
If I go on the laptop to that new directory and do a du, it says 15MB.
binary10 June 1st, 2009, 03:34 PM Good tip.
On the server side, the backup of the /etc was still 4.6MB.
I have rsynced it back to the laptop, to a new directory.
If I go on the laptop to that new directory and do a du, it says 15MB.
I think you've now confirmed that RSYNC DOES copy everything.. just tht du confusing what you had expected by counting the end link sizes.
It might also think about what you're copying, maybe you need more than just /etc of course it depends on what you are trying to do with the backup :)
Scormen June 1st, 2009, 03:37 PM Yeah, it seems to work well.
So, the "problem" where just the soft links, that couldn't be counted on the server side?
binary10 June 1st, 2009, 04:23 PM Yeah, it seems to work well.
So, the "problem" where just the soft links, that couldn't be counted on the server side?
The links were copied as links as per the design of the --archive in rsync.
The contents of the pointing links were different between your two systems. These being that that reside outside of /etc/ in /usr And so DU reporting them differently.
Scormen June 1st, 2009, 05:36 PM Okay, I got it.
Many thanks for the support, binarty10!
Scormen June 1st, 2009, 05:59 PM Just to know, is it possible to copy the data from these links as real, hard data?
binary10 June 2nd, 2009, 09:54 AM Just to know, is it possible to copy the data from these links as real, hard data?
Yep absolutely
You should then look at other possibilities of:
-L, --copy-links transform symlink into referent file/dir
--copy-unsafe-links only "unsafe" symlinks are transformed
--safe-links ignore symlinks that point outside the source tree
-k, --copy-dirlinks transform symlink to a dir into referent dir
-K, --keep-dirlinks treat symlinked dir on receiver as dir
but then you'll have to start questioning why you are backing them up like that especially stuff under /etc/. If you ever wanted to restore it you'd be restoring full files and not symlinks the restore result could be a nightmare as well as create future issues (upgrades etc) let alone your backup will be significantly larger, could be 150MB instead of 4MB.
Scormen June 2nd, 2009, 10:04 AM Okay, now I'm sure what its doing :)
Is it also possible to show on a system the "real disk usage" of e.g. that /etc directory? So, without the links, that we get a output of 4.6MB.
Thank you very much for your help!
binary10 June 2nd, 2009, 10:22 AM What does the following respond with.
sudo du --apparent-size -hsx /etc
If you want the real answer then your result from a dry-run rsync will only be enough for you.
sudo rsync --dry-run --stats -h --archive /etc/ /tmp/etc/
Aug 27, 2017 | stackoverflow.comdiff -r dir1/ dir2/ | sed '/Binary\ files\ /d' >outputfile
This recursively compares dir1 to dir2, sed removes the lines for binary files (begins with " Binary files "), then it's redirected to the outputfile.
-- Shannon VanWagner
Aug 14, 2017 | www.unix.com
06-29-2016Vikram Jain Registered UserJoin Date: Jun 2016 Last Activity: 23 March 2017, 2:57 PM EDT Posts: 3 Thanks: 3 Thanked 0 Times in 0 Posts
Cut command on RHEL 6.8 compatibility issues
We have a lot of scripts using cut as :
cut -c 0-8 --works for cut (GNU coreutils) 5.97, but does not work for cut (GNU coreutils) 8.4.
Gives error -
Code:cut: fields and positions are numbered from 1 Try `cut --help' for more information.The position needs to start with 1 for later version of cut and this is causing an issue.
Is there a way where I can have multiple cut versions installed and use the older version of cut for the user which runs the script?
or any other work around without having to change the scripts?
Last edited by RudiC; 06-30-2016 at 04:53 AM .. Reason: Added code tags.
Vikram Jain
Don Cragun AdministratorJoin Date: Jul 2012 Last Activity: 14 August 2017, 3:59 PM EDT Location: San Jose, CA, USA Posts: 10,455 Thanks: 533 Thanked 3,654 Times in 3,118 Posts
What are you trying to do when you invoke
Code:cut -c 0-8
with your old version of cut
With that old version of cut , is there any difference in the output produced by the two pipelines:
Code:echo 0123456789abcdef | cut -c 0-8
Code:echo 0123456789abcdef | cut -c 1-8
or do they produce the same output?
Don Cragun
# 06-30-2016
Vikram Jain Registered UserJoin Date: Jun 2016 Last Activity: 23 March 2017, 2:57 PM EDT Posts: 3 Thanks: 3 Thanked 0 Times in 0 Posts
I am trying to get a value from the 1st line of the file and check if that value is a valid date or not.
Below is the output for the cut command from new version
Code:$ echo 0123456789abcdef | cut -c 0-8 cut: fields and positions are numbered from 1 Try `cut --help' for more information. $ echo 0123456789abcdef | cut -c 1-8 01234567
With old version, both have same results:
Code:$ echo 0123456789abcdef | cut -c 0-8 01234567 $ echo 0123456789abcdef | cut -c 1-8 01234567
Please wrap all code, files, input & output/errors in CODE tags
It makes them far easier to read and preserves spaces for indenting or fixed-width data.
Last edited by rbatte1; 06-30-2016 at 11:38 AM .. Reason: Code tags
Vikram Jain
Scrutinizer ModeratorJoin Date: Nov 2008 Last Activity: 14 August 2017, 2:48 PM EDT Location: Amsterdam Posts: 11,509 Thanks: 497 Thanked 3,326 Times in 2,934 Posts
The use of 0 is not according to specification. Alternatively, you can just omit it, which should work across versions
Code:$ echo 0123456789abcdef | cut -c -8 01234567
If you cannot adjust the scripts, you could perhaps create a wrapper script for cut, so that the 0 gets stripped..
Last edited by Scrutinizer; 07-02-2016 at 02:28 AM ..
Vikram Jain Registered UserJoin Date: Jun 2016 Last Activity: 23 March 2017, 2:57 PM EDT Posts: 3 Thanks: 3 Thanked 0 Times in 0 Posts
Yes, don't want to adjust my scripts.
Wrapper for cut looks like something that would work.
could you please tell me how would I use it, as in, how would I make sure that the wrapper is called and not the cut command which causes the issue.
Vikram Jain
Don Cragun AdministratorJoin Date: Jul 2012 Last Activity: 14 August 2017, 3:59 PM EDT Location: San Jose, CA, USA Posts: 10,455 Thanks: 533 Thanked 3,654 Times in 3,118 Posts
The only way to make sure that your wrapper is always called instead of the OS supplied utility is to move the OS supplied utility to a different location and install your wrapper in the location where your OS installed cut originally.
Of course, once you have installed this wrapper, your code might or might not work properly (depending on the quality of your wrapper) and no one else on your system will be able to look at the diagnostics produced by scripts that have bugs in the way they specify field and character ranges so they can identify and fix their code.
My personal opinion is that you should spend time fixing your scripts that call cut -c 0.... , cut -f 0... , and lots of other possible misuses of 0 that are now correctly diagnosed as errors by the new version of cut instead of debugging code to be sure that it changes all of the appropriate 0 characters in its argument list to 1 characters and doesn't change any 0 characters that are correctly specified and do not reference a character 0 or field 0.
vgersh99 (06-30-2016), Vikram Jain (06-30-2016)
MadeInGermany ModeratorJoin Date: May 2012 Last Activity: 14 August 2017, 2:33 PM EDT Location: Simplicity Posts: 3,666 Thanks: 295 Thanked 1,226 Times in 1,108 Posts
An update of "cut" will overwrite your wrapper.
Much better: change your scripts. Run the following fix_cut script on your scripts:
Code:#!/bin/sh # fix_cut PATH=/bin:/usr/bin PRE="\b(cut\s+(-\S*\s+)*-[cf]\s*0*)0-" for arg do perl -ne 'exit 1 if m/'"$PRE"'/' "$arg" || { perl -i -pe 's/'"$PRE"'/${1}1-/g' "$arg" } doneExample: fix all .sh scripts
Code:fix_cut *.sh
The Following User Says Thank You to MadeInGermany For This Useful Post:
Vikram Jain (07-08-2016)
Jul 17, 2017 | www.linuxtoday.com
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Jul 16, 2017 | opensource.comIt's easy to get into the habit of googling anything you want to know about a command or operation in Linux, but I'd argue there's something even better: a living and breathing, complete reference, the man pages , which is short for manual pages.
The history of man pages predates Linux, all the way back to the early days of Unix. According to Wikipedia , Dennis Ritchie and Ken Thompson wrote the first man pages in 1971, well before the days of personal computers, around the time when many calculators in use were the size of toaster ovens. Man pages also have a reputation of being terse and, in a way, have a language of their own. Just like Unix and Linux, the man pages have not been static, and they continue to be developed and maintained just like the kernel.
Man pages are divided into sections referenced by numbers:
- General user commands
- System calls
- Library functions
- Special files and drivers
- File formats
- Games and screensavers
- Miscellanea
- System administration commands and daemons
Even so, users generally don't need to know the section where a particular command lies to find what they need.
The files are formatted in a way that may look odd to many users today. Originally, they were written in in an old form of markup called troff because they were designed to be printed through a PostScript printer, so they included formatting for headers and other layout aspects. In Linux, groff is used instead.
In my Fedora, the man pages are located in /usr/share/man with subdirectories (like man1 for Section 1 commands) as well as additional subdirectories for translations of the man pages.
If you look up the man page for the command man , you'll see the file man.1.gz , which is the man pages compressed with the gzip utility. To access a man page, type a command such as:man man
for example, to show the man page for man . This uncompresses the man page, interprets the formatting commands, and displays the results with less , so navigation is the same as when you use less .
All man pages should have the following subsections: Name , Synopsis , Description , Examples , and See Also . Many have additional sections, like Options , Exit Status , Environment , Bugs , Files , Author , Reporting Bugs , History , and Copyright .Breaking down a man page
To explain how to interpret a typical man page, let's use the man page for ls as an example. Under Name , we seels - list directory contents
which tells us what ls means in the simplest terms.
Under Synopsis , we begin to see the terseness:ls [ OPTION ] ... [ FILE ]
Any element that occurs inside brackets is optional. The above command means you can legitimately type ls and nothing else. The ellipsis after each element indicates that you can include as many options as you want (as long as they're compatible with each other) and as many files as you want. You can specify a directory name, and you can also use * as a wildcard. For example:ls Documents /* .txt
Under Description , we see a more verbose description of what the command does, followed by a list of the available options for the command. The first option for ls is-a, --all
do not ignore entries starting with .
If we want to use this option, we can either type the short form syntax, -a , or the long form --all . Not all options have two forms (e.g., --author ), and even when they do, they aren't always so obviously related (e.g., - F, --classify ). When you want to use multiple options, you can either type the short forms with spaces in between or type them with a single hyphen and no spaces (as long as they do not require further sub-options). Therefore,ls -a -d -l
andls -adl
are equivalent.
The command tar is somewhat unique, presumably due to its long history, in that it doesn't require a hyphen at all for the short form. Therefore,tar -cvf filearchive.tar thisdirectory /
andtar cvf filearchive.tar thisdirectory /
are both legitimate.
On the ls man page, after Description are Author , Reporting Bugs , Copyright , and See Also .
The See Also section will often suggest related man pages, so it is generally worth a glance. After all, there is much more to man pages than just commands.
- What is Linux?
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Certain commands that are specific to Bash and not system commands, like alias , cd , and a number of others, are listed together in a single BASH_BUILTINS man page. While the documentation for these is even more terse and compact, overall it contains similar information.
I find that man pages offer a lot of good, usable information, especially when I need a command I haven't used recently, and I need to brush up on the options and requirements. This is one place where the man pages' much-maligned terseness is actually very beneficial. Topics Linux About the author Greg Pittman - Greg is a retired neurologist in Louisville, Kentucky, with a long-standing interest in computers and programming, beginning with Fortran IV in the 1960s. When Linux and open source software came along, it kindled a commitment to learning more, and eventually contributing. He is a member of the Scribus Team.
Feb 25, 2017 | www.rosehosting.comcURL is very useful command line tool to transfer data from or to a server. cURL supports various protocols like FILE, HTTP, HTTPS, IMAP, IMAPS, LDAP, DICT, LDAPS, TELNET, FTP, FTPS, GOPHER, RTMP, RTSP, SCP, SFTP, POP3, POP3S, SMB, SMBS, SMTP, SMTPS, and TFTP.
cURL can be used in many different and interesting ways. With this tool you can download, upload and manage files, check your email address, or even update your status on some of the social media websites or check the weather outside. In this article will cover five of the most useful and basic uses of the cURL tool on any Linux VPS .
1. Check URL
One of the most common and simplest uses of cURL is typing the command itself, followed by the URL you want to checkcurl https://domain.com
This command will display the content of the URL on your terminal2. Save the output of the URL to a file
The output of the cURL command can be easily saved to a file by adding the -o option to the command, as shown belowcurl -o website https://domain.com % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 100 41793 0 41793 0 0 275k 0 --:--:-- --:--:-- --:--:-- 2.9M
In this example, output will be save to a file named 'website' in the current working directory.3. Download files with cURL
You can downlaod files with cURL by adding the -O option to the command. It is used for saving files on the local server with the same names as on the remote servercurl -O https://domain.com/file.zip
In this example, the 'file.zip' zip archive will be downloaded to the current working directory.
You can also download the file with a different name by adding the -o option to cURL.curl -o archive.zip https://domain.com/file.zip
This way the 'file.zip' archive will be downloaded and saved as 'archive.zip'.
cURL can be also used to download multiple files simultaneously, as shown in the example belowcurl -O https://domain.com/file.zip -O https://domain.com/file2.zip
cURL can be also used to download files securely via SSH using the following commandcurl -u user sftp://server.domain.com/path/to/file
Note that you have to use the full path of the file you want to download4. Get HTTP header information from a website
You can easily get HTTP header information from any website you want by adding the -I option (capital 'i') to cURL.curl -I http://domain.com HTTP/1.1 200 OK Date: Sun, 16 Oct 2016 23:37:15 GMT Server: Apache/2.4.23 (Unix) X-Powered-By: PHP/5.6.24 Connection: close Content-Type: text/html; charset=UTF-85. Access an FTP server
To access your FTP server with cURL use the following commandcurl ftp://ftp.domain.com --user username:password
cURL will connect to the FTP server and list all files and directories in user's home directory
You can download a file via FTPcurl ftp://ftp.domain.com/file.zip --user username:password
and upload a file ot the FTP servercurl -T file.zip ftp://ftp.domain.com/ --user username:password
You can check cURL manual page to see all available cURL options and functionalitiesman curl
Of course, if you use one of our Linux VPS Hosting services, you can always contact and ask our expert Linux admins (via chat or ticket) about cURL and anything related to cURL. They are available 24×7 and will provide information or assistance immediately.
PS. If you liked this post please share it with your friends on the social networks using the buttons below or simply leave a reply. Thanks.
Feb 20, 2017 | opensource.comAnother interesting option, and my personal favorite because it increases the power and flexibility of rsync immensely, is the --link-dest option. The --link-dest option allows a series of daily backups that take up very little additional space for each day and also take very little time to create.
Specify the previous day's target directory with this option and a new directory for today. rsync then creates today's new directory and a hard link for each file in yesterday's directory is created in today's directory. So we now have a bunch of hard links to yesterday's files in today's directory. No new files have been created or duplicated. Just a bunch of hard links have been created. Wikipedia has a very good description of hard links . After creating the target directory for today with this set of hard links to yesterday's target directory, rsync performs its sync as usual, but when a change is detected in a file, the target hard link is replaced by a copy of the file from yesterday and the changes to the file are then copied from the source to the target.
So now our command looks like the following.
rsync -aH --delete --link-dest=yesterdaystargetdir sourcedir todaystargetdir
There are also times when it is desirable to exclude certain directories or files from being synchronized. For this, there is the --exclude option. Use this option and the pattern for the files or directories you want to exclude. You might want to exclude browser cache files so your new command will look like this.
rsync -aH --delete --exclude Cache --link-dest=yesterdaystargetdir sourcedir todaystargetdir
Note that each file pattern you want to exclude must have a separate exclude option.
rsync can sync files with remote hosts as either the source or the target. For the next example, let's assume that the source directory is on a remote computer with the hostname remote1 and the target directory is on the local host. Even though SSH is the default communications protocol used when transferring data to or from a remote host, I always add the ssh option. The command now looks like this.
rsync -aH -e ssh --delete --exclude Cache --link-dest=yesterdaystargetdir remote1:sourcedir todaystargetdir
This is the final form of my rsync backup command.
rsync has a very large number of options that you can use to customize the synchronization process. For the most part, the relatively simple commands that I have described here are perfect for making backups for my personal needs. Be sure to read the extensive man page for rsync to learn about more of its capabilities as well as the options discussed here.
Feb 14, 2017 | www.linuxized.com
ed says: June 16, 2010 at 15:15
screen is really cool, and does somethings that I've yet to find counterparts to with tmux, such as the -x option:
Feb 12, 2017 | www.cyberciti.bizSo what is unique about the rsync command?
It can perform differential uploads and downloads (synchronization) of files across the network, transferring only data that has changed. The rsync remote-update protocol allows rsync to transfer just the differences between two sets of files across the network connection.How do I install rsync?
Use any one of the following commands to install rsync. If you are using Debian or Ubuntu Linux, type the following command:Always use rsync over ssh
# apt-get install rsync
$ sudo apt-get install rsync
If you are using Red Hat Enterprise Linux (RHEL) / CentOS 4.x or older version, type the following command:
# up2date rsync
RHEL / CentOS 5.x or newer (or Fedora Linux) user type the following command:
# yum install rsync
Since rsync does not provide any security while transferring data it is recommended that you use rsync over ssh session. This allows a secure remote connection. Now let us see some examples of rsync command.Comman rsync command options
Task : Copy file from a local computer to a remote server
- --delete : delete files that don't exist on sender (system)
- -v : Verbose (try -vv for more detailed information)
- -e "ssh options" : specify the ssh as remote shell
- -a : archive mode
- -r : recurse into directories
- -z : compress file data
Copy file from /www/backup.tar.gz to a remote server called openbsd.nixcraft.in
$ rsync -v -e ssh /www/backup.tar.gz email@example.com:~
Output:Password: sent 19099 bytes received 36 bytes 1093.43 bytes/sec total size is 19014 speedup is 0.99
Please note that symbol ~ indicate the users home directory (/home/jerry).Task : Copy file from a remote server to a local computer
Copy file /home/jerry/webroot.txt from a remote server openbsd.nixcraft.in to a local computer's /tmp directory:Task: Synchronize a local directory with a remote directory
$ rsync -v -e ssh email@example.com:~/webroot.txt /tmp
Task: Synchronize a remote directory with a local directory
$ rsync -r -a -v -e "ssh -l jerry" --delete /local/webroot openbsd.nixcraft.in:/webroot
Task: Synchronize a local directory with a remote rsync server or vise-versa
$ rsync -r -a -v -e "ssh -l jerry" --delete openbsd.nixcraft.in:/webroot/ /local/webroot
Task: Mirror a directory between my "old" and "new" web server/ftp
$ rsync -r -a -v --delete rsync://rsync.nixcraft.in/cvs /home/cvs
$ rsync -r -a -v --delete /home/cvs rsync://rsync.nixcraft.in/cvs
You can mirror a directory between my "old" (my.old.server.com) and "new" web server with the command (assuming that ssh keys are set for password less authentication)
$ rsync -zavrR --delete --links --rsh="ssh -l vivek" my.old.server.com:/home/lighttpd /home/lighttpd
Read related previous articles
Other options rdiff and rdiff-backup
- How do I sync data between two Load balanced Linux/UNIX servers?
- How do I sync data between two Load balanced Windows 2003 servers?
The rdiff command uses the rsync algorithm. A utility called rdiff-backup has been created which is capable of maintaining a backup mirror of a file or directory over the network, on another server. rdiff-backup stores incremental rdiff deltas with the backup, with which it is possible to recreate any backup point. Next time I will write about these utilities.rsync for Windows Server/XP/7/8
Please note if you are using MS-Windows, try any one of the program:
- DeltaCopy
- NasBackup
Further readings
=> Read rsync man page
=> Official rsync documentation
Feb 12, 2017 | www.tecmint.comThe purpose of creating a mirror of your Web Server with Rsync is if your main web server fails, your backup server can take over to reduce downtime of your website. This way of creating a web server backup is very good and effective for small and medium size web businesses. Advantages of Syncing Web Servers
The main advantages of creating a web server backup with rsync are as follows:
How To Sync Two Apache Web Servers
- Rsync syncs only those bytes and blocks of data that have changed.
- Rsync has the ability to check and delete those files and directories at backup server that have been deleted from the main web server.
- It takes care of permissions, ownerships and special attributes while copying data remotely.
- It also supports SSH protocol to transfer data in an encrypted manner so that you will be assured that all data is safe.
- Rsync uses compression and decompression method while transferring data which consumes less bandwidth.
Let's proceed with setting up rsync to create a mirror of your web server. Here, I'll be using two servers.Main Server
Backup Server
- IP Address : 192.168.0.100
- Hostname : webserver.example.com
Step 1: Install Rsync Tool
- IP Address : 192.168.0.101
- Hostname : backup.example.com
Here in this case web server data of webserver.example.com will be mirrored on backup.example.com . And to do so first, we need to install Rsync on both the server with the help of following command.[root@tecmint]# yum install rsync [On Red Hat based systems] [root@tecmint]# apt-get install rsync [On Debian based systems]Step 2: Create a User to run Rsync
We can setup rsync with root user, but for security reasons, you can create an unprivileged user on main webserver i.e webserver.example.com to run rsync.[root@tecmint]# useradd tecmint [root@tecmint]# passwd tecmint
Here I have created a user " tecmint " and assigned a password to user.Step 3: Test Rsync Setup
It's time to test your rsync setup on your backup server (i.e. backup.example.com ) and to do so, please type following command.[root@backup www]# rsync -avzhe ssh email@example.com:/var/www/ /var/wwwSample email@example.com's password: receiving incremental file list sent 128 bytes received 32.67K bytes 5.96K bytes/sec total size is 12.78M speedup is 389.70
You can see that your rsync is now working absolutely fine and syncing data. I have used " /var/www " to transfer; you can change the folder location according to your needs.Step 4: Automate Sync with SSH Passwordless Login
Now, we are done with rsync setups and now its time to setup a cron for rsync. As we are going to use rsync with SSH protocol, ssh will be asking for authentication and if we won't provide a password to cron it will not work. In order to work cron smoothly, we need to setup passwordless ssh logins for rsync.
Here in this example, I am doing it as root to preserve file ownerships as well, you can do it for alternative users too.
First, we'll generate a public and private key with following commands on backups server (i.e. backup.example.com ).[root@backup]# ssh-keygen -t rsa -b 2048
When you enter this command, please don't provide passphrase and click enter for Empty passphrase so that rsync cron will not need any password for syncing data.Sample OutputGenerating public/private rsa key pair. Enter file in which to save the key (/root/.ssh/id_rsa): Enter passphrase (empty for no passphrase): Enter same passphrase again: Your identification has been saved in /root/.ssh/id_rsa. Your public key has been saved in /root/.ssh/id_rsa.pub. The key fingerprint is: 9a:33:a9:5d:f4:e1:41:26:57:d0:9a:68:5b:37:9c:23 firstname.lastname@example.com The key's randomart image is: +--[ RSA 2048]----+ | .o. | | .. | | ..++ . | | o=E * | | .Sooo o | | =.o o | | * . o | | o + | | . . | +-----------------+
Now, our Public and Private key has been generated and we will have to share it with main server so that main web server will recognize this backup machine and will allow it to login without asking any password while syncing data.[root@backup html]# ssh-copy-id -i /root/.ssh/id_rsa.pub firstname.lastname@example.com
Now try logging into the machine, with " ssh 'email@example.com '", and check in .ssh/authorized_keys .[root@backup html]# firstname.lastname@example.com
Now, we are done with sharing keys. To know more in-depth about SSH password less login , you can read our article on it.
Step 5: Schedule Cron To Automate Sync
- SSH Passwordless Login in in 5 Easy Steps
Let's setup a cron for this. To setup a cron, please open crontab file with the following command.[root@backup ~]# crontab e
It will open up /etc/crontab file to edit with your default editor. Here In this example, I am writing a cron to run it every 5 minutes to sync the data.*/5 * * * * rsync -avzhe ssh firstname.lastname@example.com:/var/www/ /var/www/
The above cron and rsync command simply syncing " /var/www/ " from the main web server to a backup server in every 5 minutes . You can change the time and folder location configuration according to your needs. To be more creative and customize with Rsync and Cron command, you can check out our more detailed articles at:
- 10 Rsync Commands to Sync Files/Folders in Linux
- 11 Cron Scheduling Examples in Linux
Feb 12, 2017 | www.youtube.comsoundtraining.net
Keith Pawson 2 years ago
Great demonstration and very easy to follow Don! Just a note to anyone who might come across this and start using it in production based systems is that you certainly would not want to be rsyncing with root accounts. In addition you would use key based auth with SSH as an additional layer of security. Just my 2cents ;-) curtis shaw 11 months ago Best rsync tutorial on the web. Thanks.
We all know that ping command will tell you instantly whether the website is live or down. Usually, we all check whether a website is up or down like below.ping ostechnix.com -c 3
Sample output:PING ostechnix.com (18.104.22.168) 56(84) bytes of data. 64 bytes from ostechnix.com (18.104.22.168): icmp_seq=1 ttl=51 time=376 ms 64 bytes from ostechnix.com (22.214.171.124): icmp_seq=2 ttl=51 time=374 ms --- ostechnix.com ping statistics --- 3 packets transmitted, 2 received, 33% packet loss, time 2000ms rtt min/avg/max/mdev = 374.828/375.471/376.114/0.643 ms
But, Would you run this command every time to check whether your website is live or down? You may create a script to check your website status at periodic intervals. But wait. It's not necessary! Here is simple command that will watch or monitor on a regular interval.watch -n 1 curl -I http://DOMAIN_NAME/
For those who don't know, watch command is used to run any command on a particular intervals.Download Free Guide: "Introduction to Linux A Hands on Guide"
Let us check if ostechnix.com site is live or down. To do so, run:watch -n 1 curl -I https://www.ostechnix.com/
Sample output:Every 1.0s: curl -I https://www.ostechnix.com/ sk: Thu Dec 22 17:37:24 2016 % Total % Received % Xferd Average Speed Time Time Time Current Dload Upload Total Spent Left Speed 0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0 0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0 0 0 0 0 0 0 0 0 --:--:-- 0:00:01 --:--:-- 0 0 0 0 0 0 0 0 0 --:--:-- 0:00:01 --:--:-- 0 HTTP/1.1 200 OK Date: Thu, 22 Dec 2016 12:07:09 GMT Server: ApacheD Vary: Cookieh Link: <https://www.ostechnix.com/wp-json/>; rel="https://api.w.org/", <https://w p.me/5ILHv>; rel=shortlinki Content-Type: text/html; charset=UTF-8
The above command will monitor our site ostechnix.com at every one second interval. You can change the monitoring time as you wish. Unlike ping command, it will keep watching your site status until you stop it. To stop this command, press CTRL+C.
If you got HTTP/1.1 200 OK in the output, great? It means your website is working and live.
New submitter rrconan writes I always feel like I'm getting old because of the constant need to learn a new tools to do the same job. At the end of projects, I get the impression that nothing changes — there are no real benefits to the new tools, and the only result is a lot of time wasted learning them instead of doing the work. We discussed this last week with Andrew Binstock's "Just Let Me Code" article, and now he's written a follow-up about reducing tool complexity and focusing on writing code. He says, "Tool vendors have several misperceptions that stand in the way. The first is a long-standing issue, which is 'featuritis': the tendency to create the perception of greater value in upgrades by adding rarely needed features. ... The second misperception is that many tool vendors view the user experience they offer as already pretty darn good. Compared with tools we had 10 years ago or more, UIs have indeed improved significantly. But they have not improved as fast as complexity has increased. And in that gap lies the problem.' Now I understand that what I thought of as "getting old" was really "getting smart."
|_commandlinefu" href="#NEWS_TOC">
1- Save man-page as pdfman -t awk | ps2pdf - awk.pdf
2- Duplicate installed packages from one machine to the other (RPM-based systems)ssh email@example.com "rpm -qa" | xargs yum -y install
3- Stamp a text line on top of the pdf pages to quickly add some remark, comment, stamp text, … on top of (each of) the pages of the input pdf fileecho "This text gets stamped on the top of the pdf pages." | enscript -B -f Courier-Bold16 -o- | ps2pdf - | pdftk input.pdf stamp - output output.pdf
4- Display the number of connections to a MySQL Database
Count the number of active connections to a MySQL database.
The MySQL command "show processlist" gives a list of all the active clients.
However, by using the processlist table, in the information_schema database, we can sort and count the results within MySQL.mysql -u root -p -BNe "select host,count(host) from processlist group by host;" information_schema
5- Create a local compressed tarball from remote host directoryssh user@host "tar -zcf - /path/to/dir" > dir.tar.gz
This improves on #9892 by compressing the directory on the remote machine so that the amount of data transferred over the network is much smaller. The command uses ssh(1) to get to a remote host, uses tar(1) to archive and compress a remote directory, prints the result to STDOUT, which is written to a local file. In other words, we are archiving and compressing a remote directory to our local box.
6- tail a log over ssh
This is also handy for taking a look at resource usage of a remote box.ssh -t remotebox "tail -f /var/log/remote.log"
7- Print diagram of user/groups
Parses /etc/group to "dot" format and pases it to "display" (imagemagick) to show a usefull diagram of users and groups (don't show empty groups).awk 'BEGIN{FS=":"; print "digraph{"}{split($4, a, ","); for (i in a) printf "\"%s\" [shape=box]\n\"%s\" -> \"%s\"\n", $1, a[i], $1}END{print "}"}' /etc/group|display
8- Draw kernel module dependancy graph.
Parse `lsmod' output and pass to `dot' drawing utility then finally pass it to an image viewerlsmod | perl -e 'print "digraph \"lsmod\" {";<>;while(<>){@_=split/\s+/; print "\"$_[0]\" -> \"$_\"\n" for split/,/,$_[3]}print "}"' | dot -Tpng | display -
9- Create strong, but easy to remember password
Why remember? Generate!
Up to 48 chars, works on any unix-like systemread -s pass; echo $pass | md5sum | base64 | cut -c -16
10- Find all files larger than 500M and less than 1GBfind / -type f -size +500M -size -1G
11- Limit the cpu usage of a process
This will limit the average amount of CPU it consumes.sudo cpulimit -p pid -l 50
pv allows a user to see the progress of data through a pipeline, by giving information such as time elapsed, percentage completed (with progress bar), current throughput rate, total data transferred, and ETA.
To use it, insert it in a pipeline between two processes, with the appropriate options. Its standard input will be passed through to its standard output and progress will be shown on standard error.
pv will copy each supplied FILE in turn to standard output (- means standard input), or if no FILEs are specified just standard input is copied. This is the same behaviour as cat(1).
A simple example to watch how quickly a file is transferred using nc(1):
- pv file | nc -w 1 somewhere.com 3000
A similar example, transferring a file from another process and passing the expected size to pv:
- cat file | pv -s 12345 | nc -w 1 somewhere.com 3000
A more complicated example using numeric output to feed into the dialog(1) program for a full-screen progress display:
- (tar cf - . \
| pv -n -s $(du -sb . | awk '{print $1}') \
| gzip -9 > out.tgz) 2>&1 \
| dialog --gauge 'Progress' 7 70
Frequent use of this third form is not recommended as it may cause the programmer to overheat.
cgipaf is a combination of three CGI programs.
- passwd.cgi, which allow users to update their password,
- viewmailcfg.cgi, which allows users to view their current mail configuration,
- mailcfg.cgi, which updates the mail configuration.
All programs use PAM for user authentication. It is possible to run a script to update SAMBA passwords or NIS configuration when a password is changed. mailcfg.cgi creates a .procmailrc in the user's home directory. A user with too many invalid logins can be locked. The minimum and maximum UID can be set in the configuration file, so you can specify a range of UIDs that are allowed to use cgipaf.
31 Jul 2007 | www.ibm.com/developerworks
If you manage systems and networks, you need Expect.
More precisely, why would you want to be without Expect? It saves hours common tasks otherwise demand. Even if you already depend on Expect, though, you might not be aware of the capabilities described below.
Expect automates command-line interactions
You don't have to understand all of Expect to begin profiting from the tool; let's start with a concrete example of how Expect can simplify your work on AIX® or other operating systems:
Suppose you have logins on several UNIX® or UNIX-like hosts and you need to change the passwords of these accounts, but the accounts are not synchronized by Network Information Service (NIS), Lightweight Directory Access Protocol (LDAP), or some other mechanism that recognizes you're the same person logging in on each machine. Logging in to a specific host and running the appropriate
passwdcommand doesn't take long—probably only a minute, in most cases. And you must log in "by hand," right, because there's no way to script your password?
Wrong. In fact, the standard Expect distribution (full distribution) includes a command-line tool (and a manual page describing its use!) that precisely takes over this chore.
passmass(see Resources) is a short script written in Expect that makes it as easy to change passwords on twenty machines as on one. Rather than retyping the same password over and over, you can launch
passmassonce and let your desktop computer take care of updating each individual host. You save yourself enough time to get a bit of fresh air, and multiple opportunities for the frustration of mistyping something you've already entered.
The limits of Expect
passmassapplication is an excellent model—it illustrates many of Expect's general properties:
- It's a great return on investment: The utility is already written, freely downloadable, easy to install and use, and saves time and effort.
- Its contribution is "superficial," in some sense. If everything were "by the book"—if you had NIS or some other domain authentication or single sign-on system in place—or even if login could be scripted, there'd be no need for
passmass. The world isn't polished that way, though, and Expect is very handy for grabbing on to all sorts of sharp edges that remain. Maybe Expect will help you create enough free time to rationalize your configuration so that you no longer need Expect. In the meantime, take advantage of it.
- As distributed,
passmassonly logs in by way of
rlogin, or
slogin. I hope all current developerWorks readers have abandoned these protocols for
ssh, which
passmasssdoes not fully support.
- On the other hand, almost everything having to do with Expect is clearly written and freely available. It only takes three simple lines (at most) to enhance
passmassto respect
sshand other options.
You probably know enough already to begin to write or modify your own Expect tools. As it turns out, the
passmassdistribution actually includes code to log in by means of
ssh, but omits the command-line parsing to reach that code. Here's one way you might modify the distribution source to put
sshon the same footing as
telnetand the other protocols:
Listing 1. Modified passmass fragment that accepts the -ssh argument
} "-rlogin" {
set login "rlogin"
} "-slogin" {
set login "slogin"
} "-ssh" {
set login "ssh"
} "-telnet" {
set login "telnet"
In my own code, I actually factor out more of this "boilerplate." For now, though, this cascade of tests, in the vicinity of line #100 of
passmass, gives a good idea of Expect's readability. There's no deep programming here—no need for object-orientation, monadic application, co-routines, or other subtleties. You just ask the computer to take over typing you usually do for yourself. As it happens, this small step represents many minutes or hours of human effort saved.
Research and Analysis
Wednesday, April 19, 2006 5:42 PM by admin
Running Command Line Applications on Windows XP/2000 from a Linux Box:
-----Original Message-----
From: swagner@********
Sent: Thursday, April 13, 2006 2:35 PM
To: Port25 Feedback
Subject: (Port25) : You guys should look into _____
Importance: High
Can you recommend anything for running command line applications on a Windows XP/2000 box from within a program that runs on Linux? For example I want a script to run on a Linux server that will connect to a Windows server, on our network, and run certain commands.Answer:One way to do this would be to install an SSH daemon on the Windows machine and run commands via the ssh client on the Linux machine. Simply search the web for information on setting up the Cygwin SSH daemon as a service in Windows (there are docs about this everywhere). You can then run commands with ssh, somewhat like:
ssh administrator@<hostname> 'touch /cygdrive/c/blar'
That will create a file in C:\ called "blar". You can also access Windows commands if you alter the path in the Cygwin environment or use the full path to the command:
ssh administrator@<hostname> '/cygdrive/c/windows/system32/net.exe view'
re: Running Windows Command Line Applications from a Linux BoxSunday, April 23, 2006 3:44 AM by nektar
I am disappointed that Microsoft does not offer an SSH implementation with Services for Unix or with SUA.
re: Running Windows Command Line Applications from a Linux BoxSunday, April 23, 2006 4:36 PM by szlwzl
I would also very much like to see this as a built in feature - cygwin is great and I use it all the time but why not build something like this into the OS?
re: Running Windows Command Line Applications from a Linux BoxSunday, April 23, 2006 6:05 PM by breiter
I'm stunned that you didn't recommend OpenSSH running on Interix from SFU 3.5 or SUA 5.2. I would much rather rely upon Interix than Cygwin. Interopsystems maintains an both a free straight OpenSSH package and an commercial enhanced version with an MMC-based GUI configurator.
re: Running Windows Command Line Applications from a Linux BoxMonday, April 24, 2006 1:12 AM by vox
Of course if there was an RDP client that could access Windows full screen using a browser (the same way as Virtual Labs work) you could run GUI programs as well
Replies to allMonday, April 24, 2006 1:30 AM by einhverfr
Hi all.
Nektar wrote:
" I am disappointed that Microsoft does not offer an SSH implementation with Services for Unix or with SUA."
When I was at Microsoft, the legal department raised objections. Not sure if they were trademark related or what. But a good substitute would be a kerberized telnet client and server that would be capable of session encryption as per the Kerberos specification. People usually don't know that this is possible using Kerberos and telnet but it is. And given the architecture of AD, this would lead to close integration.
Vox wrote:
" Of course if there was an RDP client that could access Windows full screen using a browser (the same way as Virtual Labs work) you could run GUI programs as well"
Ever use rdesktop? It doesn;t use a browser, but it close enough you can easily run GUI apps.
Best Wishes,
Chris Travers
Metatron Technology Consulting
re: Running Windows Command Line Applications from a Linux BoxMonday, April 24, 2006 12:42 PM by docsmooth
rdesktop -0 -f <servername> will work the same as mstsc /console with the fullscreen switch set. As Chris said, it's not a browser, but it's a 100% replacement for MSTSC, and fits every single option, security and otherwise, that is in MSTSC.
Also, KDE users have "krdc" which wraps around rdesktop and VNC, so you can connect to either, and save off your settings, just like saving .RDP files in Windows.
re: Running Windows Command Line Applications from a Linux BoxMonday, April 24, 2006 4:42 PM by docsmooth
I completely forgot this portion to my previous comment:
Is there anyone who has experience running Windows Resource Kit tools or Windows 2003 Support Tools from Wine or similar directly off of the Linux box? It would be fantastic to be able to run those and the MMC tools, perhaps with WinBind as the authentication path?
As things sit right now, I have to run a VMWare WinXP instance, or dual-boot to get access to those tools that I run less frequently than certain FOSS tools, but still need.
re: Running Windows Command Line Applications from a Linux BoxThursday, April 27, 2006 4:39 PM by smither
Simply install vncserver from, for example, realvnc.com, then use vncviewer on the Linux box. You have your complete Windows desktop within a window in your X server. Open the terminal from the start menu.
re: Running Windows Command Line Applications from a Linux BoxFriday, April 28, 2006 2:49 PM by remdotc
You can either purchase a copy of Cross Over Office and/or Cedega, which allow you to run windows native binarys on linux (directX) or you can under wine get these to work, though you need to install
You need to set your 0/S in wine.conf to 2000
you need to copy most of the files contained in
sysroot/system32 to your winex install
performance is horrible
The better sollution is to install a ssh server on the windows box and then remote in via command line. If you can not afford a commerical one, you can always use cygwin
[Jan 25, 2005] Tool of the Month: ManEdit by Joe "Zonker" Brockmeier
ManEdit is provided by WolfPack Entertainment. I know, that doesn't sound like a company that would be releasing a manual page editor, but they did — and under the GNU General Public License, no less.
It's not terribly difficult to create manual pages using an editor like Emacs or Vim (see my December 2003 column if you'd like to start from scratch) but it's yet another skill that developers and admins have to tackle to learn how to write in *roff format. ManEdit actually uses an XML format that it converts to groff format when saving, so it's not necessary to delve into groff if you don't want to. (I would recommend having at least a passing familiarity with groff if you're going to be doing much development, but it's not absolutely necessary.)
ManEdit is an easy-to-use manual page editor and viewer that takes all the hassle out of creating manual pages (well, the formatting hassle, anyway — you still have to actually write the manual itself).
The ManEdit homepage has source and packages for Debian, Mandrake, Slackware, and SUSE Linux. The source should compile on FreeBSD and Solaris as well, so long as you have GTK 1.2.0. I used the SUSE packages without any problem on a SUSE 9.2 system.
Useful Solaris Commands
truss -c (Solaris >= 8): This astounding option to truss provides a profile summary of the command being trussed:$ truss -c grep asdf work.doc syscall seconds calls errors _exit .00 1 read .01 24 open .00 8 4 close .00 5 brk .00 15 stat .00 1 fstat .00 4 execve .00 1 mmap .00 10 munmap .01 3 memcntl .00 2 llseek .00 1 open64 .00 1 ---- --- --- sys totals: .02 76 4 usr time: .00 elapsed: .05
It can also show profile data on a running process. In this case, the data shows what the process did between when truss was started and when truss execution was terminated with a control-c. It's ideal for determining why a process is hung without having to wade through the pages of truss output.
truss -d and truss -D (Solaris >= 8): These truss options show the time associated with each system call being shown by truss and is excellent for finding performance problems in custom or commercial code. For example:$ truss -d who Base time stamp: 1035385727.3460 [ Wed Oct 23 11:08:47 EDT 2002 ] 0.0000 execve("/usr/bin/who", 0xFFBEFD5C, 0xFFBEFD64) argc = 1 0.0032 stat("/usr/bin/who", 0xFFBEFA98) = 0 0.0037 open("/var/ld/ld.config", O_RDONLY) Err#2 ENOENT 0.0042 open("/usr/local/lib/libc.so.1", O_RDONLY) Err#2 ENOENT 0.0047 open("/usr/lib/libc.so.1", O_RDONLY) = 3 0.0051 fstat(3, 0xFFBEF42C) = 0 . . .
truss -D is even more useful, showing the time delta between system calls:Dilbert> truss -D who 0.0000 execve("/usr/bin/who", 0xFFBEFD5C, 0xFFBEFD64) argc = 1 0.0028 stat("/usr/bin/who", 0xFFBEFA98) = 0 0.0005 open("/var/ld/ld.config", O_RDONLY) Err#2 ENOENT 0.0006 open("/usr/local/lib/libc.so.1", O_RDONLY) Err#2 ENOENT 0.0005 open("/usr/lib/libc.so.1", O_RDONLY) = 3 0.0004 fstat(3, 0xFFBEF42C) = 0
In this example, the stat system call took a lot longer than the others.
truss -T: This is a great debugging help. It will stop a process at the execution of a specified system call. ("-U" does the same, but with user-level function calls.) A core could then be taken for further analysis, or any of the /proc tools could be used to determine many aspects of the status of the process.
truss -l (improved in Solaris 9): Shows the thread number of each call in a multi-threaded processes. Solaris 9 truss -l finally makes it possible to watch the execution of a multi-threaded application.
Truss is truly a powerful tool. It can be used on core files to analyze what caused the problem, for example. It can also show details on user-level library calls (either system libraries or programmer libraries) via the "-u" option.
pkg-get: This is a nice tool (http://www.bolthole.com/solaris) for automatically getting freeware packages. It is configured via /etc/pkg-get.conf. Once it's up and running, execute pkg-get -a to get a list of available packages, and pkg-get -i to get and install a given package.
plimit (Solaris >= 8): This command displays and sets the per-process limits on a running process. This is handy if a long-running process is running up against a limit (for example, number of open files). Rather than using limit and restarting the command, plimit can modify the running process.
coreadm (Solaris >= 8): In the "old" days (before coreadm), core dumps were placed in the process's working directory. Core files would also overwrite each other. All this and more has been addressed by coreadm, a tool to manage core file creation. With it, you can specify whether to save cores, where cores should be stored, how many versions should be retained, and more. Settings can be retained between reboots by coreadm modifying /etc/coreadm.conf.
pgrep (Solaris >= 8): pgrep searches through /proc for processes matching the given criteria, and returns their process-ids. A great option is "-n", which returns the newest process that matches.
preap (Solaris >= 9): Reaps zombie processes. Any processes stuck in the "z" state (as shown by ps), can be removed from the system with this command.
pargs (Solaris >= 9): Shows the arguments and environment variables of a process.
nohup -p (Solaris >= 9): The nohup command can be used to start a process, so that if the shell that started the process closes (i.e., the process gets a "SIGHUP" signal), the process will keep running. This is useful for backgrounding a task that should continue running no matter what happens around it. But what happens if you start a process and later want to HUP-proof it? With Solaris 9, nohup -p takes a process-id and causes SIGHUP to be ignored.
prstat (Solaris >= 8): prstat is top and a lot more. Both commands provide a screen's worth of process and other information and update it frequently, for a nice window on system performance. prstat has much better accuracy than top. It also has some nice options. "-a" shows process and user information concurrently (sorted by CPU hog, by default). "-c" causes it to act like vmstat (new reports printed below old ones). "-C" shows processes in a processor set. "-j" shows processes in a "project". "-L" shows per-thread information as well as per-process. "-m" and "-v" show quite a bit of per-process performance detail (including pages, traps, lock wait, and CPU wait). The output data can also be sorted by resident-set (real memory) size, virtual memory size, execute time, and so on. prstat is very useful on systems without top, and should probably be used instead of top because of its accuracy (and some sites care that it is a supported program).
trapstat (Solaris >= 9): trapstat joins lockstat and kstat as the most inscrutable commands on Solaris. Each shows gory details about the innards of the running operating system. Each is indispensable in solving strange happenings on a Solaris system. Best of all, their output is good to send along with bug reports, but further study can reveal useful information for general use as well.
vmstat -p (Solaris >= 8): Until this option became available, it was almost impossible (see the "se toolkit") to determine what kind of memory demand was causing a system to page. vmstat -p is key because it not only shows whether your system is under memory stress (via the "sr" column), it also shows whether that stress is from application code, application data, or I/O. "-p" can really help pinpoint the cause of any mysterious memory issues on Solaris.
pmap -x (Solaris >= 8, bugs fixed in Solaris >= 9): If the process with memory problems is known, and more details on its memory use are needed, check out pmap -x. The target process-id has its memory map fully explained, as in:# pmap -x 1779 1779: -ksh Address Kbytes RSS Anon Locked Mode Mapped File 00010000 192 192 - - r-x-- ksh 00040000 8 8 8 - rwx-- ksh 00042000 32 32 8 - rwx-- [ heap ] FF180000 680 664 - - r-x-- libc.so.1 FF23A000 24 24 - - rwx-- libc.so.1 FF240000 8 8 - - rwx-- libc.so.1 FF280000 568 472 - - r-x-- libnsl.so.1 FF31E000 32 32 - - rwx-- libnsl.so.1 FF326000 32 24 - - rwx-- libnsl.so.1 FF340000 16 16 - - r-x-- libc_psr.so.1 FF350000 16 16 - - r-x-- libmp.so.2 FF364000 8 8 - - rwx-- libmp.so.2 FF380000 40 40 - - r-x-- libsocket.so.1 FF39A000 8 8 - - rwx-- libsocket.so.1 FF3A0000 8 8 - - r-x-- libdl.so.1 FF3B0000 8 8 8 - rwx-- [ anon ] FF3C0000 152 152 - - r-x-- ld.so.1 FF3F6000 8 8 8 - rwx-- ld.so.1 FFBFE000 8 8 8 - rw--- [ stack ] -------- ------- ------- ------- ------- total Kb 1848 1728 40 -
Here we see each chunk of memory, what it is being used for, how much space it is taking (virtual and real), and mode information.
df -h (Solaris >= 9): This command is popular on Linux, and just made its way into Solaris. df -h displays summary information about file systems in human-readable form:$ df -h Filesystem size used avail capacity Mounted on /dev/dsk/c0t0d0s0 4.8G 1.7G 3.0G 37% / /proc 0K 0K 0K 0% /proc mnttab 0K 0K 0K 0% /etc/mnttab fd 0K 0K 0K 0% /dev/fd swap 848M 40K 848M 1% /var/run swap 849M 1.0M 848M 1% /tmp /dev/dsk/c0t0d0s7 13G 78K 13G 1% /export/home
Each administrator has a set of tools used daily, and another set of tools to help in a pinch. This column included a wide variety of commands and options that are lesser known, but can be very useful. Do you have favorite tools that have saved you in a bind? If so, please send them to me so I can expand my tool set as well. Alternately, send along any tools that you hate or that you feel are dangerous, which could also turn into a useful column!
What makes a good utility?
There is a wonderful discussion of this question in The UNIX Programming Environment, by Kernighan & Pike. A good utility is one that does its job as well as possible. It has to play well with others; it has to be amenable to being combined with other utilities. A program that doesn't combine with others isn't a utility; it's an application.
Utilities are supposed to let you build one-off applications cheaply and easily from the materials at hand. A lot of people think of them as being like tools in a toolbox. The goal is not to have a single widget that does everything, but to have a handful of tools, each of which does one thing as well as possible.
Some utilities are reasonably useful on their own, whereas others imply cooperation in pipelines of utilities. Examples of the former include
grep. On the other hand,
xargsis rarely used except with other utilities, most often
What language to write in?
Most of the UNIX system utilities are written in C. The examples here are in Perl and sh. Use the right tool for the right job. If you use a utility heavily enough, the cost of writing it in a compiled language might be justified by the performance gain. On the other hand, for the fairly common case where a program's workload is light, a scripting language may offer faster development.
If you aren't sure, you should use the language you know best. At least when you're prototyping a utility, or figuring out how useful it is, favor programmer efficiency over performance tuning. Most of the UNIX system utilities are in C, simply because they're heavily used enough to justify the development cost. Perl and sh (or ksh) can be good languages for a quick prototype. Utilities that tie other programs together may be easier to write in a shell than in a more conventional programming language. On the other hand, any time you want to interact with raw bytes, C is probably looming on your horizon.
Designing a utility
A good rule of thumb is to start thinking about the design of a utility the second time you have to solve a problem. Don't mourn the one-off hack you write the first time; think of it as a prototype. The second time, compare what you need to do with what you needed to do the first time. Around the third time, you should start thinking about taking the time to write a general utility. Even a merely repetitive task might merit the development of a utility; for instance, many generalized file-renaming programs have been written based on the frustration of trying to rename files in a generalized way.
Here are some design goals of utilities; each gets its own section, below.
- Do one thing well.
- Be a filter.
- Generalize.
- Be robust.
- Be new.
Do one thing well
Do one thing well; don't do multiple things badly. The best example of this doing one thing well is probably
sort. No utilities other than
sorthave a sort feature. The idea is simple; if you only solve a problem once, you can take the time to do it well.
Imagine how frustrating it would be if most programs sorted data, but some supported only lexographic sorts, while others supported only numeric sorts, and a few even supported selection of keys rather than sorting by whole lines. It would be annoying at best.
When you find a problem to solve, try to break the problem up into parts, and don't duplicate the parts for which utilities already exist. The more you can focus on a tool that lets you work with existing tools, the better the chances that your utility will stay useful.
You may need to write more than one program. The best way to solve a specialized task is often to write one or two utilities and a bit of glue to tie them together, rather than writing a single program to solve the whole thing. It's fine to use a 20-line shell script to tie your new utility together with existing tools. If you try to solve the whole problem at once, the first change that comes along might require you to rethink everything.
I have occasionally needed to produce two-column or three-column output from a database. It is generally more efficient to write a program to build the output in a single column and then glue it to a program that puts things in columns. The shell script that combines these two utilities is itself a throwaway; the separate utilities have outlived it.
Some utilities serve very specialized needs. If the output of
lsin a crowded directory scrolls off the screen very quickly, it might be because there's a file with a very long name, forcing
lsto use only a single column for output. Paging through it using
moretakes time. Why not just sort lines by length, and pipe the result through
tail, as follows?
Listing 1. One of the smallest utilities anywhere, sl
#/usr/bin/perl -w print sort { length $a <=> length $b } <>;
The script in Listing 1 does exactly one thing. It takes no options, because it needs no options; it only cares about the length of lines. Thanks to Perl's convenient
<>idiom, this automatically works either on standard input or on files named on the command line.
Be a filter
Almost all utilities are best conceived of as filters, although a few very useful utilities don't fit this model. (For instance, a program that counts might be very useful, even though it doesn't work well as a filter. Programs that take only command-line arguments as input, and produce potentially complicated output, can be very useful.) Most utilities, though, should work as filters. By convention, filters work on lines of text. Most filters should have some support for running on multiple input files.
Remember that a utility needs to work on the command line and in scripts. Sometimes, the ideal behavior varies a little. For instance, most versions of
lsautomatically sort input into columns when writing to a terminal. The default behavior of
grepis to print the file name in which a match was found only if multiple files were specified. Such differences should have to do with how users will want the utility to work, not with other agendas. For instance, old versions of GNU
bcdisplayed an intrusive copyright notice when started. Please don't do that. Make your utility stick to doing its job.
Utilities like to live in pipelines. A pipeline lets a utility focus on doing its job, and nothing else. To live in a pipeline, a utility needs to read data from standard input and write data to standard output. If you want to deal with records, it's best if you can make each line be a "record." Existing programs such as
joinare already thinking that way. They'll thank you for it.
One utility I occasionally use is a program that calls other programs iteratively over a tree of files. This makes very good use of the standard UNIX utility filter model, but it only works with utilities that read input and write output; you can't use it with utilities that operate in place, or take input and output file names.
Most programs that can run from standard input can also reasonably be run on a single file, or possibly on a group of files. Note that this arguably violates the rule against duplicating effort; obviously, this could be managed by feeding
catinto the next program in the series. However, in practice, it seems to be justified.
Some programs may legitimately read records in one format but produce something entirely different. An example would be a utility to put material into columnar form. Such a utility might equate lines to records on input, but produce multiple records per line on output.
Not every utility fits entirely into this model. For instance,
xargstakes not records but names of files as input, and all of the actual processing is done by some other program.
Try to think of tasks similar to the one you're actually performing; if you can find a general description of these tasks, it may be best to try to write a utility that fits that description. For instance, if you find yourself sorting text lexicographically one day and numerically another day, it might make sense to consider attempting a general sort utility.
Generalizing functionality sometimes leads to the discovery that what seemed like a single utility is really two utilities used in concert. That's fine. Two well-defined utilities can be easier to write than one ugly or complicated one.
Doing one thing well doesn't mean doing exactly one thing. It means handling a consistent but useful problem space. Lots of people use
grep. However, a great deal of its utility comes from the ability to perform related tasks. The various options to
grepdo the work of a handful of small utilities that would have ended up sharing, or duplicating, a lot of code.
This rule, and the rule to do one thing, are both corollaries of an underlying principle: avoid duplication of code whenever possible. If you write a half-dozen programs, each of which sorts lines, you can end up having to fix similar bugs half a dozen times instead of having one better-maintained
sortprogram to work on.
This is the part of writing a utility that adds the most work to the process of getting it completed. You may not have time to generalize something fully at first, but it pays off when you get to keep using the utility.
Sometimes, it's very useful to add related functionality to a program, even when it's not quite the same task. For instance, a program to pretty-print raw binary data might be more useful if, when run on a terminal device, it threw the terminal into raw mode. This makes it a lot easier to test questions involving keymaps, new keyboards, and the like. Not sure why you're getting tildes when you hit the delete key? This is an easy way to find out what's really getting sent. It's not exactly the same task, but it's similar enough to be a likely addition.
errnoutility in Listing 2 below is a good example of generalizing, as it supports both numeric and symbolic names.
Be robust
It's important that a utility be durable. A utility that crashes easily or can't handle real data is not a useful utility. Utilities should handle arbitrarily long lines, huge files, and so on. It is perhaps tolerable for a utility to fail on a data set larger than it can hold in memory, but some utilities don't do this; for instance,
sort, by using temporary files, can generally sort data sets much larger than it can hold in memory.
Try to make sure you've figured out what data your utility can possibly run on. Don't just ignore the possibility of data you can't handle. Check for it and diagnose it. The more specific your error messages, the more helpful you are being to your users. Try to give the user enough information to know what happened and how to fix it. When processing data files, try to identify exactly what the malformed data was. When trying to parse a number, don't just give up; tell the user what you got, and if possible, what line of the input stream the data was on.
As a good example, consider the difference between two implementations of
dc. If you run
dc /home, one of them says "Cannot use directory as input!" The other just returns silently; no error message, no unusual exit code. Which of these would you rather have in your path when you make a typo on a
cdcommand? Similarly, the former will give verbose error messages if you feed it the stream of data from a directory, perhaps by doing
dc < /home. On the other hand, it might be nice for it to give up early on when getting invalid data.
Security holes are often rooted in a program that isn't robust in the face of unexpected data. Keep in mind that a good utility might find its way into a shell script run as root. A buffer overflow in a program such as
findis likely to be a risk to a great number of systems.
The better a program deals with unexpected data, the more likely it is to adapt well to varied circumstances. Often, trying to make a program more robust leads to a better understanding of its role, and better generalizations of it.
Be new
One of the worst kinds of utility to write is the one you already have. I wrote a wonderful utility called
count. It allowed me to perform just about any counting task. It's a great utility, but there's a standard BSD utility called
jotthat does the same thing. Likewise, my very clever program for turning data into columns duplicates an existing utility,
rs, likewise found on BSD systems except that
rsis much more flexible and better designed. See Resources below for more information on
If you're about to start writing a utility, take a bit of time to browse around a few systems to see if there might be one already. Don't be afraid to steal Linux utilities for use on BSD, or BSD utilities for use on Linux; one of the joys of utility code is that almost all utilities are quite portable.
Don't forget to look at the possibility of combining existing applications to make a utility. It is possible, in theory, that you'll find stringing existing programs together is not fast enough, but it's very rare that writing a new utility is faster than waiting for a slightly slow pipeline.
An example utility
In a sense this program is a counterexample, in that it is never useful as a filter. It works very well as a command-line utility, however.
This program does one thing only. It prints out errno lines from /usr/include/sys/errno.h in a slightly pretty-printed format. For instance:
$ errno 22
EINVAL [22]: Invalid argument
Listing 2. Errno finder
#!/bin/sh usage() { echo >&2 "usage: errno [numbers or error names]\n" exit 1 } for i do case "$i" in [0-9]*) awk '/^#define/ && $3 == '"$i"' { for (i = 5; i < NF; ++i) { foo = foo " " $i; } printf("%-22s%s\n", $2 " [" $3 "]:", foo); foo = "" }' < /usr/include/sys/errno.h ;; E*) awk '/^#define/ && $2 == "'"$i"'" { for (i = 5; i < NF; ++i) { foo = foo " " $i; } printf("%-22s%s\n", $2 " [" $3 "]:", foo); foo = "" }' < /usr/include/sys/errno.h ;; *) echo >&2 "errno: can't figure out whether '$i' is a name or a number." usage ;; esac done
Does it generalize? Yes, nicely. It supports both numeric and symbolic names. On the other hand, it doesn't know about other files, such as /usr/include/sys/signal.h, that are likely in the same format. It could easily be extended to do that, but for a convenience utility like this, it's easier to just make a copy called "signal" that reads signal.h, and uses "SIG*" as the pattern to match a name.
This is just a tad more convenient than using
grepon system header files, but it's less error-prone. It doesn't produce garbled results from ill-considered arguments. On the other hand, it produces no diagnostic if a given name or number is not found in the header. It also doesn't bother to correct some invalid inputs. Still, as a command-line utility never intended to be used in an automated context, it's okay.
Another example might be a program to unsort input (see Resources for a link to this utility). This is simple enough; read in input files, store them in some way, then generate a random order in which to print out the lines. This is a utility of nearly infinite applications. It's also a lot easier to write than a sorting program; for instance, you don't need to specify which keys you're not sorting on, or whether you want things in a random order alphabetically, lexicographically, or numerically. The tricky part comes in reading in potentially very long lines. In fact, the provided version cheats; it assumes there will be no null bytes in the lines it reads. It's a lot harder to get that right, and I was lazy when I wrote it.
If you find yourself performing a task repeatedly, consider writing a program to do it. If the program turns out to be reasonable to generalize a bit, generalize it, and you will have written a utility.
Don't design the utility the first time you need it. Wait until you have some experience. Feel free to write a prototype or two; a good utility is sufficiently better than a bad utility to justify a bit of time and effort on researching it. Don't feel bad if what you thought would be a great utility ends up gathering dust after you wrote it. If you find yourself frustrated by your new program's shortcomings, you just had another prototyping phase. If it turns out to be useless, well, that happens sometimes.
The thing you're looking for is a program that finds general application outside your initial usage patterns. I wrote
unsortbecause I wanted an easy way to get a random series of colors out of an old X11 "rgb.txt" file. Since then, I've used it for an incredible number of tasks, not the least of which was producing test data for debugging and benchmarking sort routines.
One good utility can pay back the time you spent on all the near misses. The next thing to do is make it available for others, so they can experiment. Make your failed attempts available, too; other people may have a use for a utility you didn't need. More importantly, your failed utility may be someone else's prototype, and lead to a wonderful utility program for everyone.
- The UNIX Programming Environment by Brian W. Kernighan and Rob Pike (Prentice Hall, Inc., 1984) is an essential part of any programmer's bookshelf. You can also download all the example code for this book on the Bell Labs' CSR page.
- Download core, file, shell, and text utilities from the GNU Web site software pages.
- You can download the source code for the "unsort" utility described in this article.
- More information about the BSD utilities jot and rs are available on freshmeat.
- Read more best practices and hints on getting started coding in "Developing a Linux command-line utility" (developerWorks, June 2002).
- Learn how to write secure applications, validate and check inputs, prevent buffer overflows, and more with David Wheeler's Secure programmer column on developerWorks.
- The "Bash by example" series on developerWorks will help you get started writing shell scripts.
- The tutorial "Building a cross-platform C library" shows how to convert an existing C program or module -- or utility -- into a shared library (developerWorks, June 2001).
- Peter Seebach has previously written a series on how to treat UNIX utilities as a component architecture on developerWorks.
- Get the developerWorks Subscription (formerly the Toolbox subscription) to get CDs and downloads of the latest software from IBM to build, test, evaluate, and demonstrate applications on the IBM Software Development Platform.
- For Linux tools on AIX, check out the AIX toolbox for Linux applications.
- To develop an application on Linux using trial versions of the latest IBM tools and products, visit the Speed-start your Linux app site.
- Find more resources for Linux developers in the developerWorks Linux section.
"What is it about m4 that makes it so useful, and yet so overlooked? m4 -- a macro processor -- unfortunately has a dry name that disguises a great utility. A macro processor is basically a program that scans text and looks for defined symbols, which it replaces with other text or other symbols."
The ps command can tell you quite a few things about each process running on your system. These include the process owner, memory use, accumulated time, the process status (e.g., waiting on resources) and many other things as well. But one thing that ps cannot tell you is what a process is doing - what files it is using, what ports it has opened, what libraries it is using and what system calls it is making. If you can't look at source code to determine how a program works, you can tell a lot about it by using a procedure called "tracing". When you trace a process (e.g., truss date), you get verbose commentary on the process' actions. For example, you will see a line like this each time the program opens a file:
open("/usr/lib/libc.so.1", O_RDONLY) = 4
The text on the left side of the equals sign clearly indicates what is happening. The program is trying to open the file /usr/lib/libc.so.1 and it's trying to open it in read-only mode (as you would expect, given that this is a system library). The right side is not nearly as self-evident. We have just the number 4. Open is not a Unix command, of course, but a system call. That means that you can only use the command within a program. Due to the nature of Unix, however, system calls are documented in man pages just like ls and pwd.
To determine what this number represents, you can skip down in this column or you can read the man page. If you elect to read the man page, you will undoubtedly read a line that tells you that the open() function returns a file descriptor for the named file. In other words, the number, 4 in our example, is the number of the file descriptor referred to in this open call. If the process that you are tracing opens a number of files, you will see a sequence of open calls. With other activity removed, the list might look something like this:
open("/dev/zero", O_RDONLY) = 3
open("/var/ld/ld.config", O_RDONLY) Err#2 ENOENT
open("/usr/lib/libc.so.1", O_RDONLY) = 4
open("/usr/lib/libdl.so.1", O_RDONLY) = 4
open64("./../", O_RDONLY|O_NDELAY) = 3
open64("./../../", O_RDONLY|O_NDELAY) = 3
open("/etc/mnttab", O_RDONLY) = 4
Notice that the first file handle is 3 and that file handles 3 and 4 are used repeatedly. The initial file handle is always 3. This indicates that it is the first file handle following those that are the same for every process that you will run - 0, 1 and 2. These represent standard in, standard out and standard error.
The file handles shown in the example truss output above are repeated only because the associated files are subsequently closed. When a file is closed, the file handle that was used to access it can be used again.
The close commands include only the file handle, since the location of the file is known. A close command would, therefore, be something like close(3). One of the lines shown above displays a different response - Err#2
ENOENT. This "error" (the word is put in quotes because this does not necessarily indicate that the process is defective in any way) indicates that the file the open call is attempting to open does not exist. Read "ENOENT" as "No such file".
Some open calls place multiple restrictions on the way that a file is opened. The open64 calls in the example output above, for example, specify both O_RDONLY and O_NDELAY. Again, reading the man page will help you to understand what each of these specifications means and will present with a list of other options as well.
As you might expect, open is only one of many system calls that you will see when you run the truss command. Next week we will look at some additional system calls and determine what they are doing.
Exploring processes with Truss: part 2 By Sandra Henry-Stocker
While truss and its cousins on non-Solaris systems (e.g., strace on Linux and ktrace on many BSD systems) provide a lot of data on what a running process is doing, this information is only useful if you know what it means. Last week, we looked at the open call and the file handles that are returned by the call to open(). This week, we look at some other system calls and analyze what these system calls are doing. You've probably noticed that the nomenclature for system functions is to follow the name of the call with a set of empty parentheses for example, open(). You will see this nomenclature in use whenever system calls are discussed.
The fstat() and fstat64() calls obtains information about open files - "fstat" refers to "file status". As you might expect, this information is retrieved from the files' inodes, including whether or not you are allowed to read the files' contents. If you trace the ls command (i.e., truss ls), for example, your trace will start with lines that resemble these:
1 execve("/usr/bin/ls", 0x08047BCC, 0x08047BD4) argc = 1
2 open("/dev/zero", O_RDONLY) = 3
3 mmap(0x00000000, 4096, PROT_READ|PROT_WRITE|PROT_EXEC, MAP_PRIVATE, 3, 0) = 0xDFBFA000
4 xstat(2, "/usr/bin/ls", 0x08047934) = 0
5 open("/var/ld/ld.config", O_RDONLY) Err#2 ENOENT
6 sysconfig(_CONFIG_PAGESIZE) = 4096
7 open("/usr/lib/libc.so.1", O_RDONLY) = 4
8 fxstat(2, 4, 0x08047310) = 0
28 lstat64(".", 0x080478B4) = 0
29 open64(".", O_RDONLY|O_NDELAY) = 3
30 fcntl(3, F_SETFD, 0x00000001) = 0
31 fstat64(3, 0x0804787C) = 0
32 brk(0x08057208) = 0
33 brk(0x08059208) = 0
34 getdents64(3, 0x08056F40, 1048) = 424
35 getdents64(3, 0x08056F40, 1048) = 0
36 close(3) = 0
In line 31, we see a call to fstat64, but what file is it checking? The man page for the fstat() and your intuition are probably both telling you that this fstat call is obtaining information on the file opened two lines before – "." or the current directory - and that it is referring to this file by its file handle (3) returned by the open() call in line
2. Keep in mind that a directory is simply a file, though a different variety of file, so the same system calls are used as would be used to check a text file.
You will probably also notice that the file being opened is called /dev/zero (again, see line 2). Most Unix sysadmins will immediately know that /dev/zero is a special kind of file - primarily because it is stored in /dev. And, if moved to look more closely at the file, they
will confirm that the file that /dev/zero points to (it is itself a symbolic link) is a special character file. What /dev/zero provides to system programmers, and to sysadmins if they care to use it, is an endless stream of zeroes. This is more useful than might first appear.
To see how /dev/zero works, you can create a 10M-byte file full of zeroes with a command like this:
/bin/dd < /dev/zero > zerofile bs=1024 seek=10240 count=1
This command works well because it creates the needed file with only a few read and write operations; in other words, it is very efficient.
You can verify that the file is zero-filled with od.
# od -x zerofile
0000000 0000 0000 0000 0000 0000 0000 0000 0000
Each string of four zeros (0000) represents two bytes of data. The * on the second line of output indicates that all of the remaining lines are identical to the first.
Looking back at the truss output above, we cannot help but notice that the first line of the truss output includes the name of the command that we are tracing. The execve() system call executes a process. The first argument to execve() is the name of the file from which the new process
image is to be loaded. The mmap() call which follows maps the process image into memory. In
other words, it directly incorporates file data into the process address space. The getdents64() calls on lines 34 and 35 are extracting information from the directory file - "dents" refers to "directory entries'.
The sequence of steps that we see at the beginning of the truss output executing the entered command, opening /dev/zero, mapping memory and so on - looks the same whether you are tracing ls, pwd, date or restarting Apache. In fact, the first dozen or so lines in your truss output will be nearly identical regardless of the command you are running. You should, however, expect to see some differences between different Unix systems and different versions of Solaris.
Viewing the output of truss, you can get a solid sense of how the operating system works. The same insights are available if you are tracing your own applications or troubleshooting third party executables.
Sandra Henry-Stocker
3.2. Displaying all processes owned by a specific user$ ps ux USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND heyne 691 0.0 2.4 19272 9576 ? S 13:35 0:00 kdeinit: kded heyne 700 0.1 1.0 5880 3944 ? S 13:35 0:01 artsd -F 10 -S 40 ... ... ...
You can also use the syntax "ps U username".
As you can see, the ps command can give you a lot of interesting information. If you for example want to know what your friend actually does, just replace your login name with her/his name and you see all processe belonging to her/him.
3.3. Own output format
If you are bored by the regular output, you could simply change the format. To do so use the formatting characters which are supported by the ps command.
If you execute the ps command with the 'o' parameter you can tell the ps command what you want to see:
Odd display with AIX field descriptors:
$ ps -o "%u : %U : %p : %a" RUSER : USER : PID : COMMAND heyne : heyne : 3363 : bash heyne : heyne : 3367 : ps -o %u : %U : %p : %a
-n -- to number lines
-s -- delete multiple blank lines
-v -- display non-pronting characters
One incarnation of the so called 80/20 rule has been associated with software systems. It has been observed that 80% of a user population regularly uses only 20% of a system's features. Without backing this up with hard statistics, my 20+ years of building and using software systems tells me that this hypothesis is probably true. The collection of Linux command-line programs is no exception to this generalization. Of the dozens of shell-level commands offered by Linux, perhaps only ten commands are commonly understood and utilized, and the remaining majority are virtually ignored.
Which of these dogs of the Linux shell have the most value to offer? I'll briefly describe ten of the less popular but useful Linux shell commands, those which I have gotten some mileage from over the years. Specifically, I've chosen to focus on commands that parse and format textual content.
The working examples presented here assume a basic familiarity with command-line syntax, simple shell constructs and some of the not-so-uncommon Linux commands. Even so, the command-line examples are fairly well commented and straightforward. Whenever practical, the output of usage examples is presented under each command-line execution.
The following eight commands parse, format and display textual content. Although not all provided examples demonstrate this, be aware that the following commands will read from standard input if file arguments are not presented.
Table 1. Summary of Commands
As their names imply, head and tail are used to display some amount of the top or bottom of a text block. head presents beginning of a file to standard output while tail does the same with the end of a file. Review the following commented examples:## (1) displays the first 6 lines of a file head -6 readme.txt ## (2) displays the last 25 lines of a file tail -25 mail.txt
Here's an example of using head and tail in concert to display the 11th through 20th line of a file.# (3) head -20 file | tail -10
Manual pages show that the tail command has more command-line options than head. One of the more useful tail option is -f. When it is used, tail does not return when end-of-file is detected, unless it is explicitly interrupted. Instead, tail sleeps for a period and checks for new lines of data that may have been appended since the last read.## (4) display ongoing updates to the given ## log file tail -f /usr/tmp/logs/daemon_log.txt
Imagine that a dæmon process was continually appending activity logs to the /usr/adm/logs/daemon_log.txt file. Using
tail -fat a console window, for example, will more or less track all updates to the file in real time. (The -f option is applicable only when tail's input is a file).
If you give multiple arguments to tail, you can track several log files in the same window.## track the mail log and the server error log ## at the same time. tail -f /var/log/mail.log /var/log/apache/error_log
tac--Concatenate in Reverse
What is cat spelled backwards? Well, that's what tac's functionality is all about. It concatenates file order and their contents in reverse. So what's its usefulness? It can be used on any task that requires ordering elements in a last-in, first-out (LIFO) manner. Consider the following command line to list the three most recently established user accounts from the most recent through the least recent.# (5) last 3 /etc/passwd records - in reverse $ tail -3 /etc/passwd | tac curly:x:1003:100:3rd Stooge:/homes/curly:/bin/ksh larry:x:1002:100:2nd Stooge:/homes/larry:/bin/ksh moe:x:1001:100:1st Stooge:/homes/moe:/bin/ksh
nl--Numbered Line Output
nl is a simple but useful numbering filter. I displays input with each line numbered in the left margin, in a format dictated by command-line options. nl provides a plethora of options that specify every detail of its numbered output. The following commented examples demonstrate some of of those options:# (6) Display the first 4 entries of the password # file - numbers to be three columns wide and # padded by zeros. $ head -4 /etc/passwd | nl -nrz -w3 001 root:x:0:1:Super-User:/:/bin/ksh 002 daemon:x:1:1::/: 003 bin:x:2:2::/usr/bin: 004 sys:x:3:3::/: # # (7) Prepend ordered line numbers followed by an # '=' sign to each line -- start at 101. $ nl -s= -v101 Data.txt 101=1st Line ... 102=2nd Line ... 103=3rd Line ... 104=4th Line ... 105=5th Line ... .......
The fmt command is a simple text formatter that focuses on making textual data conform to a maximum line width. It accomplishes this by joining and breaking lines around white space. Imagine that you need to maintain textual content that was generated with a word processor. The exported text may contain lines whose lengths vary from very short to much longer than a standard screen length. If such text is to be maintained in a text editor (like vi), fmt is the command of choice to transform the original text into a more maintainable format. The first example below shows fmt being asked to reformat file contents as text lines no greater than 60 characters long.# (8) No more than 60 char lines $ fmt -w 60 README.txt > NEW_README.txt # # (9) Force uniform spacing: # 1 space between words, 2 between sentences $ echo "Hello World. Hello Universe." | fmt -u -w80 Hello World. Hello Universe.
fold--Break Up Input
fold is similar to fmt but is used typically to format data that will be used by other programs, rather than to make the text more readable to the human eye. The commented examples below are fairly easy to follow:# (10) Format text in 3 column width lines $ echo oxoxoxoxo | fold -w3 oxo xox oxo # (11) Parse by triplet-char strings - # search for 'xox' $ echo oxoxoxoxo | fold -w3 | grep "xox" xox # (12) One way to iterate through a string of chars $ for i in $(echo 12345 | fold -w1) > do > ### perform some task ... > print $i > done 1 2 3 4 5
pr shares features with simpler commands like nl and fmt, but its command-line options make it ideal for converting text files into a format that's suitable for printing. pr offers options that allow you to specify page length, column width, margins, headers/footers, double line spacing and more.
Aside from being the best suited formatter for printing tasks, pr also offers other useful features. These features include allowing you to view multiple files vertically in adjacent columns or columnizing a list in a fixed number of columns (see Listing 2).
Listing 2. Using pr
The following two commands are specialized parsers used to pick apart file path pieces.
The basename and dirname commands are useful for presenting portions of a given file path. Quite often in scripting situations, it's convenient to be able to parse and capture a file name or the containing-directory name portions of a file path. These commands reduce this task to a simple one-line command. (There are other ways to approach this using the Korn shell or sed "magic", but basename and dirname are more portable and straightforward).
basename is used to strip off the directory, and optionally, the file suffix parts of a file path. Consider the following trivial examples::# (21) Parse out the Java Class name $ basename /usr/local/src/java/TheClass.java .java TheClass # (22) Parse out the file name. $ basename srcs/C/main.c main.c
dirname is used to display the containing directory path, as much of the path as is provided. Consider the following examples:# (23) absolute and relative directory examples $ dirname /homes/curly/.profile /homes/curly $ dirname curly/.profile curly # # (24) From any korn-shell script, the following # line will assign the directory from where # the script was launched SCRIPT_HOME="$(dirname $(whence $0))" # # (25) # Okay, how about a non-trivial practical example? # List all directories (under $PWD that contain a # file called 'core'. $ for i in $(find $PWD -name core )^ > do > dirname $i > done | sort -u bin rje/gcc src/C
ttyrec is a tty recorder. Recorded data can be played back with the included ttyplay command.
ttyrec is just a derivative of script command for recording timing information with microsecond accuracy as well.
It can record emacs -nw, vi, lynx, or any programs running on tty.
In the next few articles, I'd like to take a look at backups and archiving utilities. if you're like I was when I started using Unix, I was intimidated by the words
dump, and a quick peek at their respective man pages did not alleviate my fears.
Links to the manuals for the Gnu tools most commonly used in embedded development: Using and Porting GNU CC * Using as, The GNU Assembler * GASP, an assembly preprocessor * Using ld, the GNU linker
Slashdot Articles Free Books Online Matt Braithwaite writes "Answering RMS's call for free documentation, Karl Fogel has written a book on CVS that is free (GPLed) and available online. (The paper version has additional non-free material.) " Also, edinator wrote to say that ORA has put the Using Samba text online. The entire text of the Oreilly Docbook is downloadable www.docbook.org
|TheLinuxGurus.org: Book Review: Professional Linux Programming
(Oct 21, 2000, 18:38 UTC) (116 reads) (0 talkbacks) (Posted by
"This book takes a different approach in that it steps through the development of a fictional application. The application you will build is an interface for a DVD rental store."
|FreeOS.com: RPM usage for newbies
(Oct 21, 2000, 18:03 UTC) (203 reads) (0 talkbacks) (Posted by
"The Red Hat Package Manager (RPM) has establised itself as one of the most popular distrubution formats for linux software today. A first time user may feel overwhelmed by the vast number of options available and this article will help a newbie to get familiar with usage of this tool."
Signal Ground: Stupid dd Tricks (or, Why We Didn't buy Norton Ghost)
"The company that employs Tom and me builds big pieces of food processing machinery that cost upwards of $400K. Each machine includes an embedded PCs running -- and I cringe -- NT 4. While the company's legacy currently dictates NT, those of us at the lower levels of the totem pole work to wedge Linux in wherever we can. What follows is a short story of a successful insertion that turned out to be (gasp!) financially beneficial to the company, too."
"...Ghost works well; it does exactly what we wanted it to. You boot off of a floppy (while the image medium is in another drive), and Ghost does the rest. The problem lies in Ghost's licensing. If you want to install in a situation like ours, you have to purchase a Value-Added Reseller (VAR) license from Symantec. And, every time you create a drive, you have to pay them about 17 dollars. When you also figure in the time needed to keep track of those licenses, that adds up in a hurry."
"It finally occurred to me that we could use Linux and a couple of simple tools (dd, gzip, and a shell script) to do the same thing as Ghost -- at least as far as our purposes go. ... The Results? We showed our little program to management, and they were impressed. We were able to create disk images almost as quickly as Norton Ghost, and we did it all in an afternoon using entirely free software. The rest is history."
Issue #87 Common Shell Tools - Focus On Linux - 05-25-00
"sort and uniq
The sort command is used to sort the lines in an input stream in alphanumeric or telephone book order. The simplest ways to use sort are to provide it with a filename to sort or an input stream whose data should be output in sorted form:sort myfile.txt cat myfile.txt | sort
This tool can be told to sort based on alternate fields and in several different orders. The uniq command is often used in conjunction with sort because it removes consecutive duplicate lines from and input stream before writing them to standard output. This provides a quick easy way to sort a pool of data and them remove duplicate entries.
A more in-depth discussion of sort can be found in the past QuickTip called Sort and Uniq.
The tr command in its simplest form can be thought of as a simpler case of the sed command discussed earlier. It is used to replace all occurances of a single character in an input stream with an alternate character before writing to the output stream. For example, to change all percent (%) characters to spaces, you might use:tr '%' ' '
Though sed can be used to accomplish the same task, it is often simpler to use tr when replacing a single character because the syntax is easy to remember and many special characters which must be escaped for sed can be supplied to tr without escaping.
The wc, or "word count" command does just what its name implies: it counts words. As an added feature, tr also counts lines and bytes. The formats for counting words, lines, or bytes in a file or input stream are:$ wc -w myfile.txt 897 myfile.txt $ wc -l myfile.txt 193 myfile.txt $ wc -c myfile.txt 5927 myfile.txt $
Notice that the output for wc normally includes the filename (when reading from a file) and always includes a number of spaces as well. Often, this behavior is undesirable, usually when a number is required without leading or trailing whitespace. In such cases, sed and cut can be used to eliminate them:$ wc -l myfile.txt | cut -d ' ' -f 1 | sed 's! !!g' 193 $
Note that other methods for removing spaces or filenames include using a more complex sed command alone or even using awk, which we won't discuss in this issue.
The xargs utility is used to break long input streams into groups of lines so that the shell isn't overloaded by command substitution. For example, the following command may fail if too many files are present in the current directory tree for BASH to substitute correctly:lpr $(find .)
However, using xargs, the desired effect can be obtained:find . | xargs lpr
More information on using xargs can be found in the QuickTip called Long Argument Lists and on the xargs manual page.
Linux Today PRNewswire SCO Contributes to the Open Source Community; Kicks Off Open Source Initiatives
"SCO is contributing source code for two developer tools -- "cscope" and "fur." The code is released under the terms of the BSD License and will be maintained by SCO. The first technology, cscope, is available to download at www.sco.com/opensource. Software developers can use cscope to help design and debug programs coded with the C programming language. The second technology, Fur, will be available to download in several weeks. Fur is a real-time analysis program used to optimize application and system binaries for more effective run time execution. Dramatic results have been seen in high-level applications and database systems using fur."
[Jan 30, 2000] Use the Source, Luke Compiling and installing from source code LG #49
One of the greatest strengths of the Open Source movement is the availability of source code for almost every program. This article will discuss in general terms, with some examples, how to install a program from source code rather than a precompiled binary package. The primary audience for this article is the user who has some familiarity with installing programs from binaries, but isn't familiar with installing from source code. Some knowledge of compiling software is helpful, but not required.
[Jan 3, 2000]
Programming in Expect A Bulletproof Interface LG #48 -- very interesting and
useful paper. See also:
Ext2- Automating
interactive tasks with expect and crontab
QCad the user-friendly CAD system for Linux is now open source PC Week PC Week Labs evaluates open-source apps
They recommend Apache, Mozilla, Samba and Perl for enterprise use. Evaluations of a particular product are second-rate and does not deserve attention. Only the list is interesting [Jan 25, 1999] Win32 Editors page was added Open Source Software Chronicles -- October-December, 1998
Open Source Software Chronicles -- July-September, 1998
Open Source Software Chronicles -- April-June, 1998
Open Source Software Chronicles -- Jan-March, 1998
open_source.shtml -- collection of links with materials defending open source movement from oversimplifications.
Softpanorama hot topic of the month
Linux, Unix, -etc Using the m4 Macro Processor nice m4 intro by Paul Dunne
"What is it about m4 that makes it so useful, and yet so overlooked? m4 -- a macro processor -- unfortunately has a dry name that disguises a great utility. A macro processor is basically a program that scans text and looks for defined symbols, which it replaces with other text or other symbols."
GNU macro processor - Table of Contents
docs.sun.com Programming Utilities Guide/m4
m4 macro processor Caldera
Programming in standard C and C++
m4 macro processor
Defining macros
Arithmetic built-ins
File inclusion
System command
String manipulation
General Programming Concepts Writing and Debugging Programs - m4 Macro Processor Overview
This chapter provides information about the m4 macro processor, which is a front-end processor for any programming language being used in the operating system environment.
The m4 macro processor is useful in many ways. At the beginning of a program, you can define a symbolic name or symbolic constant as a particular string of characters. You can then use the m4 program to replace unquoted occurrences of the symbolic name with the corresponding string. Besides replacing one string of text with another, the m4 macro processor provides the following features:
- Arithmetic capabilities
- File manipulation
- Conditional macro expansion
- String and substring functions
The m4 macro processor processes strings of letters and digits called tokens. The m4 program reads each alphanumeric token and determines if it is the name of a macro. The program then replaces the name of the macro with its defining text, and pushes the resulting string back onto the input to be rescanned. You can call macros with arguments, in which case the arguments are collected and substituted into the right places in the defining text before the defining text is rescanned.
The m4 program provides built-in macros such as define. You can also create new macros. Built-in and user-defined macros work the same way.
configure.in examples see
also the Tcl/Tk distribution
acmacros (smr_macros)
Macros for GNU autoconf. The highlight is a set of three macros to ease checking for 3rd party libraries. The macros were originally available here as acmacros.
Matthew Langston took the macros, cleaned them up, and wrote documentation for them. This much-improved version is now known as smr_macros, available here or in Matthew Langston's SLAC archive. (Matthew also distributes RPMs)
Less sucks less more than more.
That's why I use more less, and less more.
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The Last but not Least
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