Editing Group identifier (section)

== Personal groups ==

Many system administrators allocate for each user also a personal primary group that has the same name as the user's login name, and often also has the same numeric GID as the user's UID. Such personal groups have no other members and make collaboration with other users in shared directories easier, by allowing users to habitually work with <code>[[umask]] 0002</code>. This way, newly created files can have by default write permissions enabled for group members, because this will normally only enable write access for members of the personal group, that is only for the file's owner. However, if a file is created in a shared directory that belongs to another group and has the [[setgid]] bit set, then the created file will automatically become writable to members of that directory's group as well.

On many Linux systems, the <code>USERGROUPS_ENAB</code> variable in <code>/etc/login.defs</code> controls whether commands like <code>useradd</code> or <code>userdel</code> automatically add or delete an associated personal group.