I have a file that a colleague and I are editing together, on a Unix system. We are using Unix group permissions to edit it. We have one Unix group that we are both members of. Whenever I save the file, it changes the Unix group to one that he is not a member of. Is there any way to stop it from doing that?


5 Answers 5


Your options are to set the setgid bit (chmod g+s) on the directory to make files created within it match its group ID, or to use the newgrp command to open a shell with the desired group ID before editing the file.

  • 1
    I'm not sure this is correct. I think what the what he needs is the setgid bit, not to the sticky bit. From Wikipedia: Setting the setgid permission on a directory (chmod g+s) causes new files and subdirectories created within it to inherit its group ID, rather than the primary group ID of the user who created the file. Activating the sticky bit on the directory will only make sure that only the directories' files' owner, the directory's owner or root can modify the directories' files. Oct 21, 2011 at 23:09

One option is to switch group using the command newgrp. It may ask for the group password that you may set with gpasswd.


Uno. change your default login group number to be the same between the two people

# Where 514 is the group id.

Duo: create a new user id , with a password only known by the two people involved. chown the file to be owned by the new userid. Before editing the file in question, suto the new userid.


cp $EDITOR to $HOME; \# in this example pico
chmod g+s $HOME/pico;


sudo chgrp RELEVANTGROUP some/path/to/file \# may require root

Cinco: Create a few Google account and edit the thing SIMULTANEOUSLY in Google docs. (it is neat to watch where the other person is typing). Make a point of changing the sharing perms in Google Docs for "anyone with the link"

Hexo: Split the file in two and have each editor only work on half.


Take a look at umask on your system.

  • OK, default dot files set by our sys admins use a umask of 022. What's a good umask for "don't change it!"?
    – asbruckman
    Mar 13, 2009 at 14:22
  • 3
    umask is for default permissions, not group ID.
    – moonshadow
    Mar 13, 2009 at 14:33

Here is a good article about Sticky-Bit and other advanced permission settings: https://notes-from-a-dev.blogspot.com/2011/03/modes-and-permission-sticky-bit.html

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