TL;DR Is there a way under Linux to know which file access caused an hard disk to   spin up?   Full story My laptop has a NVME disk, which contains the operating system and my home dir, and a spinning hard disk, which contains a second home dir which I use to store bulk data that do not fit on the NVME. I believe it is a common arrangement.  One of the nice things is this layout is that when I am not working on the projects that require files on the spinning disk, the disk itself can spin down, saving on energy, battery time, noise, etc. And this happens quite frequently.  However, every now and then the hard disk spins up even if what I am doing in that moment has no clear link with data that are stored there. It is still a consequence of an action done by me, not of a cron script or something else, because it still happens as a consequence of my doing something, like opening an application. However I cannot see what opening that application should produce an access to the spinning disk, knowing which file are supposed to be there. So I would like to understand more of what happens, and this justifies the question above.
I have a 24/7 always-on Debian Jessie based headless home server that has a large 1TB SSD for the OS and all of my frequently accessed files. This same system has 4 larger hard disk drives in a SnapRAID array. These are mainly for archiving infrequently accessed Blu-rays and want those drives to remain spun down in standby unless I actually read or write to them. They are all formatted as ext4 and mounted with noatime and nodiratime enabled.  So even though no process or program should be regularly accessing those drives in any direct way, the hard drives constantly get spun up from standby. It seems to be related to graphical programs that provide a gui file browser, even something like Chromium. If I don't even browse into those drives, I'm thinking that these processes by simply getting a list of available drives spins up the hard disks. Much like blkid does. The problem is, it's hard to determine the root cause of this since none of these processes are actually reading or writing the filesystem on those drives, so no files are actually changing or being touched. Is there some sort of cache that I can populate or a buffer to prevent these programs from spinning up the hard drive simply by getting a list of available disks? This is honestly driving me insane, since I can't find a reliably way to keep these disks spun-down even though there is no direct access of the filesystem.  UPDATE: Thanks to Stephen's answer, I was able to trace the disk activity to gvfs and udisks. It's a real shame that these processes insist on waking up disks in standby when they aren't actually being accessed to do any real I/O with the filesystem. So far I just uninstalled them, knowing that it will remove some functionality from PCManFM and the like.
Algorithm to see if two voxels are interconnected If you draw two cards, what is the probability that the second card is a queen? Problem with glossary I am copying the very first piece of code from  in order to create a glossary. While I get no problem in the compilation I do not get the "glossary part" that appears in the example. I literally copy paste.  Also, I want to create a document that only consists of a glossary of various terms. That is to put everything in alphabetical order (with the possibility to include references as well). How could I possibly do this? I tried some itemize options with alphabetical order but does not look that good. Multi-OS Portable TeX system I'm looking to treat myself to a totally portable TeX system and was wondering: is it possible to devise an installation scheme that would run on Windows, Linux and MacOS at the "same" time?  I think TeXLive is the best choice here, but I'd much rather avoid having to maintain three separate TeXLive installations. I'd like the three installations to share the package databases for instance.  I'll be using a 32Gb USB stick, in case it matters.  PS: I think I'm onto something here... will post back when I have a working prototype.  Edit: after reading  I managed to format a USB stick with UDF and have it read and written in Linux and Windows (need to perform some tests on Mac yet). This is the first step towards interoperability.  Edit 2: well, as it turns out, the previous note was useless (the partition table breaks under Windows), I've found  and it works like a charm. The only remaining step is writing a couple of scripts to set the environmental variables and we're done ;) Beginner here with an issue on a simple presentation using beamer  \documentclass{beamer}  \begin{document} \begin{frame}   \tau \epsilon \chi \end{frame} \end{document}   The above fails with the message "! Missing $ inserted." and waits for me to do something when converting to pdf. I have tried adding the instruction \usepackage[utf8]{inputenc} and also \usepackage[greek]{babel}. I have not seen references either to needing to use any other package. What is exactly I am missing? I am trying to understand the permission usage for the cp command in unix.   What are the permissions required for copying a file into a directory What are the permissions required for copying out of a directory?   I'm assuming for my first question, the directory will need execute permissions to perform the operation and the file will need read permissions to read the binary of the file and then the output file will need write permissions.  For the second the directory itself would need execute permissions to perform the copy operation and the file would need read permissions to extract the data from the file.  Can anyone tell me if my logic is flawed? As I understand it, electromagnetic waves have two components which are the result of each other, i.e., when a moving electric charge creates a changing magnetic field at point X then a changing electric field is created at point Y and this repeating process is what creates EM waves, so therefore, it requires no medium. Is my understanding correct?  One thing that I'm surprised to know is that light is also called an electromagnetic wave.  Does this include light of any kind, for example: light from a bulb, a tube, and also from the Sun? How do they contain electric and magnetic fields? How can I get my external IP address in a shell script? Recently, I read in the journal  that Stephen Hawking wrote a paper claiming that black holes do not exist.  How is this possible? Please explain it to me because I didn't understand what he said.  References:   Article in Nature News:  (Zeeya Merali, January 24, 2014). S. Hawking, Information Preservation and Weather Forecasting for Black Holes, . Book where human thoughts are affecting the universe Basically our thoughts are ruining everything. Like when humans are taught stars are giant balls of gas. To the rest of the universe they aren't but humans think it and destroy alien planets. I think they come to seal us off from the rest of the universe. I have six upvotes for the one question with no intervening history. They have been summarised into two groups - one with 4 events and one with 2 events. However, when you expand either, both show all 6 events. Minor I know, just letting you know. decode a quoted printable message in php I have the string which that encoded in .  How do I decode this in php?  Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Vestibulum felis = pede, vestibulum et, ullamcorper in, ultrices eget, metus. Suspendisse in n= ulla. Sed justo. Donec dapibus auctor neque. Pellentesque faucibus ante nec=  metus. Vivamus feugiat, velit rhoncus semper suscipit, libero augue venena= tis leo, nec ornare nulla elit eget diam. Nullam sollicitudin. Is there a way to add a timer to a Beamer presentation? I have seen presentations in Power Point which contain a timer. Can this be done in Beamer using a simple command, or maybe a package? If not a timer, is it possible to at least get a clock on your slides? Let $D = B(0,1) \subset \mathbb{C} $ a disc, $f$ holomorphic on $D$. I want to demonstrate that if $$ 2|f^{'}(0)| = \sup_{z, w \in D} |f(z)-f(w)|$$  then $f$ is linear.   I know this is a well-known result. Where can I find the proof ? Invert "if" statement to reduce nesting When I ran  on my code, for example:      if (some condition)     {         Some code...                 }   ReSharper gave me the above warning (Invert "if" statement to reduce nesting), and suggested the following correction:     if (!some condition) return;    Some code...   I would like to understand why that's better. I always thought that using "return" in the middle of a method problematic, somewhat like "goto". Show current ping to website on Taksbar I'm looking for a way to monitor my current internet connection quality by showing the ping-response to a website like google in the taskbar on the right side. I'm using Windows 8.1. Kind of like , but for the ping. Any suggestions?  I want to stop using the command line to ping Google. How are the number of views in a question calculated? I saw it's not just a page views number, because, if I press F5 several times, it won't increase the number of views.  They could store my IP address in a table, but wouldn't that make it slow? They would need to query a database one more time for each request. How can I get a copy of a Canadian visa refusal letter? I have applied for a Canadian Temporary Resident Visa (TRV); a previous paper application was refused in 2016. I have lost the copy of my refusal letter and want to submit it when I apply for my new visa. How how can I get the a copy of the 2016 refusal letter from Embassy? Is it safe to use file's hash as IV? I'm encrypting some files using AES in CBC mode.    I'm also using file's digest (SHA-1) to check that data is decrypted correctly (so I need to store it with file).  Is it safe to use this digest as AES's IV and store it in the header of file? Or it has security issue? This is a summary of the excerpt:  Given that we have:  *$10^9$ people  *each person has a chance of 0.01 of going to a hotel  *we have $10^5$ hotels, each hotel holds 100 people  *Thus, $P(2 \text{ persons meet on the same hotel in any given day}) = 0.01 \cdot 0.01 \cdot 10^{-5}$  *and $P(2\text{ persons on the same hotel in $2$ day}) = P(2 \text{ persons on the same hotel in any given days})^2 = 10^{-18}$  the book "Mining of Massive Dataset" said that the expected number of pairs who stay in the same hotel for 2 days is:  $P(2 \text{ persons on the same hotel in $2$ days}) \cdot ( \text{number of pairs of people} ) \cdot (\text{number of pairs of days})$  this is the part where I got stuck. Can't understand how it come to this derivation. Can anybody explain it in more elaborate detail.  You can find the content on page 6 of this link:  (it is freely available)