Is it possible to test effective permissions of a file for a specific user?

I normally do this by su user and then accessing the file, but I now want to test this on an user with no shell (i.e. a System user)


The sudo command can run anything as a particular user with the -u option. Instead of worrying about shells, just try to cat (or execute, whatever) your file as your target user:

$ sudo -u apache cat .ssh/authorized_keys 
cat: .ssh/authorized_keys: Permission denied
  • 1
    cat is probably not the best choice though... it you are testing a large file or a binary file... – Alexis Wilke Nov 14 '15 at 6:29
  • Your example is flawed though; SSH requires particular permissions set on .ssh (u=rwx,g=,o=) and its children (u=rw,g=r,o=r) or it will refuse to use the entire config for that user. This does not test that. – detly Sep 13 '20 at 23:35

I found convenient to use in scripts something like

 sudo -u <user> test -r <file-to-test> && ...
  • 2
    best answer, as you can test for readable (-r), writable (-w) and executable (-x) without actually modifying/creating the file. man test for more details – Thomas Jul 1 '14 at 18:18
sudo -u <user> test -r <file-to-test>; echo $?

The echo $? part will output the exit status from the test.

Just remember here that the output will be 0 if the operation was successful! Or non-zero, e.g. 1, if not.

Like @Thomas's comment on @user72025's answer, use man test to get more operation tests, like test -x to test executability, test -w for writability, etc.

  • 1
    For me, this is the most helpful answer. The one by user72025 was close, but I had no idea what the result was. You've made that clear. Thanks. Voting up. – inspirednz Feb 15 '18 at 2:41

I've found you can use su -s <shellname> <username> to enter a specific shell as a specific user. You can then test file permissions as usual.


su -s /bin/bash Debian-exim
touch /etc/exim4/exim4.conf.template
  • Very interesting option. – Alex Mar 5 '19 at 8:27

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.