Specify default group and permissions for new files in a certain directory

Question

I have a certain directory in which there is a project shared by multiple users. These users use SSH to gain access to this directory and modify/create files.

This project should only be writeable to a certain group of users: lets call it "mygroup". During an SSH session, all files/directories created by the current user should by default be owned by group "mygroup" and have group-writeable permissions.

I can solve the permissions problem with umask:

$ cd project
$ umask 002
$ touch test.txt

File "test.txt" is now group-writeable, but still belongs to my default group ("mislav", same as my username) and not to "mygroup". I can chgrp recursively to set the desired group, but I wanted to know is there a way to set some group implicitly like umask changes default permissions during a session.

This specific directory is a shared git repo with a working copy and I want git checkout and git reset operations to set the correct mask and group for new files created in the working copy. The OS is Ubuntu Linux.

Update: a colleague suggests I should look into getfacl/setfacl of POSIX ACL but the solution below combined with umask 002 in the current session is good enough for me and is much more simple.

Answer 1

In order to have all files under a given directory inherit group rights, you need to use the setgid bit on your directory. See this link.

 $ mkdir test
 $ sudo chown raphink.staff test
 $ ls -lhd test
     drwxr-xr-x 2 raphink staff 4.0K 2009-12-21 16:19 test
 $ sudo chmod g+s test # Set the setgid bit
 $ ls -lhd test
     drwxr-sr-x 2 raphink staff 4.0K 2009-12-21 16:21 test
 $ touch test/foo
 $ ls -lh test
     total 0
     -rw-r--r-- 1 raphink staff 0 2009-12-21 16:23 foo

Answer 2

I'm not much of an expert when it comes to the *nix side, but I think what you're looking for is called setgid.

See here.

Answer 3

It is difficult to inherit parent directory permissions in Linux/UNIX without using ACLs. but there is a way to assign default file permissions, check bellow link

Can you inherit parent directory permissions.