← Home

How SGID works on Linux

Feb 10, 2026 · 3 min read permissions

One day you run the command ls -lha and notice that a directory has a “strange” permission: instead of the letter x in the group, the letter s appears. What does this mean? What is the difference between x and s?

In this article, you will learn about SGID, how it works, and how it can help with shared directories for development teams.

The problem

By default, when a user creates a file or directory in Linux, the group of the file will be the user’s primary group.

This can cause problems in development teams. For example:

  • Suppose we have two developers: mary and joseph.
  • Each one creates files in a shared folder.
  • Result without SGID:
$ ls -lha /srv/dev
-rw-rw-r-- 1 joseph  joseph   0 Feb 10 21:35 a
-rw-rw-r-- 1 mary    mary     0 Feb 10 21:35 b

The file created by Joseph belongs to the joseph group, and Mary’s file belongs to the mary group. Joseph cannot modify Mary’s files, and vice versa, even if they are in the same work folder.

What is SGID?

The SGID (Set Group ID) is a special permission that can be applied to directories.

When a directory has SGID, all files and subdirectories created within it inherit the group of the parent directory, not the group of the user who created them.

In ls -l, the permission appears as s instead of x for the group:

drwxrws---  3 root dev  4.0K Feb 10 20:23 dev
  • x — you can enter the directory
  • s — you can enter + files inherit the parent group

Settings

Creating the directory and group

$ mkdir -p /srv/dev
$ groupadd dev
$ chgrp dev /srv/dev
$ chmod 770 /srv/dev/

Creating users and adding them to the group

$ useradd joseph -m -s /bin/bash
$ useradd mary -m -s /bin/bash
$ usermod -aG dev joseph
$ usermod -aG dev mary

Without SGID

If both create files in the /srv/dev folder:

$ ls -lha /srv/dev
-rw-rw-r-- 1 joseph  joseph   0 Feb 10 21:35 a
-rw-rw-r-- 1 mary    mary     0 Feb 10 21:35 b

Each file still belongs to the user group, not the dev group. This is not ideal for collaboration.

Applying SGID

First, we set all files to the correct group:

$ chgrp -R dev /srv/dev

Now all files belong to the dev group:

$ ls -lha /srv/dev
-rw-rw-r-- 1  joseph  dev  0 Feb 10 21:35 a
-rw-rw-r-- 1  mary    dev  0 Feb 10 21:35 b

Finally, we apply SGID to the folder:

$ chmod 2770 /srv/dev/

The 2 at the beginning activates SGID. The folder now has rwxrws--- permissions.

Result

If Joseph creates a new file:

$ su joseph
$ touch /srv/dev/c
$ ls -lha /srv/dev
-rw-rw-r-- 1 joseph dev 0 Feb 10 21:35 c

And Maria creates another file:

$ su mary
$ touch /srv/dev/d
$ ls -lha /srv/dev
-rw-rw-r-- 1 mary dev 0 Feb 10 21:35 d

All files belong to the dev group, facilitating collaboration.

Conclusion

SGID is a powerful permission for shared directories:

  • Files created inherit the parent directory group
  • Facilitates team collaboration without having to manually change permissions
  • Always combine SGID with appropriate group permissions to maintain security