The options which apply to the groupmod command are:
-g, --gid GID
The value of GID must be a non-negative decimal integer. This value must be unique, unless the -o option is used. Values between 0 and 999 are typically reserved for system groups.
Any files that have the old group ID and must continue to belong to GROUP, must have their group ID changed manually.
-n, --new-name NEW_GROUP
-p, --password PASSWORD
Note: This option is not recommended because the password (or encrypted password) will be visible by users listing the processes.
You should make sure the password respects the system's password policy.
The following configuration variables in /etc/login.defs change the behavior of this tool:
The default value is 0, meaning that there are no limits in the number of members in a group.
This feature (split group) permits to limit the length of lines in the group file. This is useful to make sure that lines for NIS groups are not larger than 1024 characters.
If you need to enforce such limit, you can use 25.
Note: split groups may not be supported by all tools (even in the Shadow toolsuite). You should not use this variable unless you really need it.
The groupmod command exits with the following values:
chfn(1), chsh(1), passwd(1), gpasswd(8), groupadd(8), groupdel(8), useradd(8), userdel(8), usermod(8).