chmod doesn't work in exec in java
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I'm changing file permission with this code:  
    
    Runtime.getRuntime().exec("chmod 600 '/home/user/Desktop/file'");

But it has no effect!
Before and after code execution `ls -l /home/user/Desktop/file` reports:

    -rw-rw-r-- 1 evir evir 7928 Jul 31 14:54 file

What is the problem?