Managing Group Accounts (Files and Commands)

/etc/group contains group account information.

Format:
groupname:password: GID:userlist

e.g.:

admin:x:119:diane
ssh:x:109:

/etc/gshadow contains group passwords.

Format:
groupname:password:administrators:members

e.g.:

diane:!::

Commands:

chage – change user password expiry information

gpasswd – change group membership, group passwords

groupadd – create a group

groupdel – delete a group

groupmod – modify a group

grpconv – moves all group password information to /etc/gshadow

grpunconv – creates group from group and gshadow and then removes gshadow

Shared password is not recommended, so do not use group passwords unless necessary.

In adding a user to a group, usermod removes user from any groups not specified, instead use gpasswd. gpasswd adds the new user without removing the new user from any existing group memberships.
syntax:
gpasswd -a user group

chown and chgrp

To change file ownership, use chown command. And to change the group where a file belong to, use chgrp command.

change file owner:

chown user file

change file owner and group:

chown user:group file

change only the group:

chgrp user file