Checks are made to verify that each entry has:
The checks for correct number of fields and unique group name are fatal. If an entry has the wrong number of fields, the user will be prompted to delete the entire line. If the user does not answer affirmatively, all further checks are bypassed. An entry with a duplicated group name is prompted for deletion, but the remaining checks will still be made. All other errors are warnings and the user is encouraged to run the groupmod command to correct the error.
The commands which operate on the /etc/group and /etc/gshadow files are not able to alter corrupted or duplicated entries. grpck should be used in those circumstances to remove the offending entries.
The -r and -s options cannot be combined.
The options which apply to the grpck command are:
-R, --root CHROOT_DIR
By default, grpck operates on /etc/group and /etc/gshadow. The user may select alternate files with the group and shadow parameters.
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 grpck command exits with the following values:
group(5), groupmod(8), gshadow(5), passwd(5), pwck(8), shadow(5).