Group Management

All files in Linux are owned by either a user and a group. You can see which user and group own a file using ls -l.

$ ls -l
-rw-r--r--  1 tym tym 2464 Jun  2 08:05 README.md
               ^   ^
             User Group

Groups are very useful for access control. Giving a group ownership over a file makes all its members owners of that file.

Just as you have /etc/passwd for user management, you have /etc/group for group management. Similar to how new human users get UIDs from 1000 onwards, human groups get group IDS (GID) from 1000 onwards too. GIDs lower than 1000 are usually intended for system users as opposed to human users.

$ cat /etc/group | grep "docker"
docker:x:966:tym
              ^
	members in the group

Commands to know about:

• groups — what groups you’re a member of.
  • groups $USERNAME for groups a specific user is in.
• groupadd
  • Analogous to useradd in user management.
• groupdel
  • Analogous to userdell user management.
• usermod --append --groups $GROUP — add user to a group.