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10-and-Local-Groups.md

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Managing Local Group Accounts

Objectives

After completing this section, you should be able to:

  • Create, modify, and delete local group accounts.

Creating Groups from the Command Line

  • Create a New Group:

    groupadd groupname
    • Uses the next available GID from the range specified in the /etc/login.defs file.

  • Specify a GID for the Group:

    groupadd -g GID groupname
    • Example: 
      sudo groupadd -g 10000 group01
tail /etc/group

Note:

  • Automatic creation of user private groups (GID 1000+) means it is recommended to set aside a range of GIDs for supplementary groups to avoid collision with system groups (GID 0-999).

  • Create a System Group:

    groupadd -r groupname
    • Uses a GID from the range of valid system GIDs listed in /etc/login.defs.
    • Example: 
      sudo groupadd -r group02
tail /etc/group

Modifying Existing Groups from the Command Line

  • Change Group Name:

    groupmod -n newgroupname oldgroupname
    • Example: 
      sudo groupmod -n group0022 group02
tail /etc/group

  • Change GID:

    groupmod -g newGID groupname
    • Example: 
      sudo groupmod -g 20000 group0022
tail /etc/group

Deleting Groups from the Command Line

  • Remove a Group: 
    groupdel groupname
    • Example: 
      sudo groupdel group0022

Note:

  • You cannot remove a group if it is the primary group of any existing user.
  • Check all file systems to ensure that no files remain on the system that are owned by the group.

Changing Group Membership from the Command Line

  • Change a User's Primary Group:

    usermod -g groupname username
    • Example: 
      id user02
sudo usermod -g group01 user02
id user02

  • Add a User to a Supplementary Group:

    usermod -aG groupname username
    • Example: 
      id user03
sudo usermod -aG group01 user03
id user03

Important:

  • The -a option makes usermod function in append mode. Without -a, the user will be removed from any of their current supplementary groups that are not included in the -G option's list.

References

  • group(5), groupadd(8), groupdel(8), and usermod(8) man pages