groupadd

What it does

Groups give the same rights to many users, for example write access to a shared folder. The groups are in /etc/group and /etc/gshadow. The GID comes from the range in /etc/login.defs (GID_MIN … GID_MAX) unless you give one.

groupmod renames a group or changes its GID. groupdel removes a group, but not if it is the primary group of a user.

Add members with usermod -aG GROUP USER or gpasswd -a USER GROUP.

How to write it

groupadd [OPTION]... GROUP
groupmod [OPTION]... GROUP
groupdel [OPTION]... GROUP

Options 17

Most used

-g, --gid GID: Use this GID.
-r, --system: Create a system group (GID under 1000).
-f, --force: Exit with success if the group already exists (and pick another GID if -g is used).
-o, --non-unique: Allow a GID that is used already (with -g).
-U, --users USER1[,USER2...]: Add these users as members right away.
-K, --key KEY=VALUE: Override a value of /etc/login.defs (like GID_MIN).
-p, --password HASH: Set a hashed group password (not recommended).
-R, --root DIR: Work in this chroot folder.
-P, --prefix DIR: Use the files under this prefix folder.
-h, --help: Show help.

groupmod

-n, --new-name NEW_GROUP: Rename the group.
-g, --gid GID: Change the GID (files keep the old number; fix them with find).
-a, --append: With -U: add the users to the members (do not replace).
-U, --users USER1[,USER2...]: Set the member list.
-o, --non-unique: Allow a GID that is used already.
-p, --password HASH: Change the hashed group password.

groupdel

-f, --force: Delete the group even if it is the primary group of a user.

Examples 11

$ run as a normal user# run as root (or with sudo)

1Create a group
```
#groupadd webadmins
```
Gets the next free GID.
2Create a group with a fixed GID
```
#groupadd -g 3000 sales
```
Same GID on all servers for NFS shares.
3Create a system group for a service
```
#groupadd -r appsvc
```
GID under 1000.
4Create a group with members
```
#groupadd -U anna,bob projectx
```
Newer versions only; else use gpasswd -a.
5Rename a group
```
#groupmod -n web-admins webadmins
```
Members and files keep working: they use the GID.
6Change the GID and fix the files
```
#groupmod -g 3100 sales
#find / -xdev -gid 3000 -exec chgrp -h sales {} +
```
Files still have the old number until you change them.
7Delete a group
```
#groupdel projectx
```
Fails if it is the primary group of a user.
8Set up a shared team folder
```
#groupadd sales
#mkdir /srv/sales
#chgrp sales /srv/sales; chmod 2770 /srv/sales
```
2 = setgid: new files get the group sales (see the permissions chapter).
9Do not fail when the group exists (scripts)
```
#groupadd -f sales
```
Safe to run twice, for example in Ansible-like scripts.
10Check the group
```
$getent group sales
sales:x:3000:anna,bob
```
Name, password placeholder, GID, members.
11Find groups with no members (cleanup)
```
#awk -F: '$4 == "" && $3 >= 1000 {print $1}' /etc/group
```
Private groups of users are listed too; they are normal.

Watch out

groupdel does not change files: they then show the old GID number.
A user gets new groups only after a new login.

Files

/etc/group, /etc/gshadow: The group data.
/etc/login.defs: GID_MIN, GID_MAX, SYS_GID_MIN, SYS_GID_MAX.

Exit codes

0 :: Done. 2 :: Wrong syntax. 3 :: Wrong value for an option. 4 :: The GID is used already. 6 :: The group does not exist (groupmod, groupdel). 8 :: Cannot delete the primary group of a user (groupdel). 9 :: The group name is used already. 10 :: Could not update the group file.

`groupadd`

What it does

How to write it

Options 17

groupadd

groupmod

groupdel

Examples 11

1Create a group

2Create a group with a fixed GID

3Create a system group for a service

4Create a group with members

5Rename a group

6Change the GID and fix the files

7Delete a group

8Set up a shared team folder

9Do not fail when the group exists (scripts)

10Check the group

11Find groups with no members (cleanup)

Watch out

Files

Exit codes

Full manual

groupadd

What it does

How to write it

Options 17

groupadd

groupmod

groupdel

Examples 11

1Create a group

2Create a group with a fixed GID

3Create a system group for a service

4Create a group with members

5Rename a group

6Change the GID and fix the files

7Delete a group

8Set up a shared team folder

9Do not fail when the group exists (scripts)

10Check the group

11Find groups with no members (cleanup)

Watch out

Files

Exit codes

Related commands

Used in these lessons

Used in these labs

Full manual

`groupadd`