grpck − verify integrity of group files

grpck [options] [group [ shadow ]]

     The grpck command verifies the integrity of the groups
information. It checks that all entries in /etc/group and
/etc/gshadow have the proper format and contain valid data.
The user is prompted to delete entries that are improperly
formatted or which have other uncorrectable errors.

     Checks are made to verify that each entry has:

 •   the correct number of fields

 •   a unique and valid group name

 •   a valid group identifier (/etc/group only)

 •   a valid list of members and administrators

 •   a corresponding entry in the /etc/gshadow file
     (respectively /etc/group for the gshadow checks)

     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:

     −h, −−help
     Display help message and exit.

     −r, −−read−only
     Execute the grpck command in read−only mode. This
     causes all questions regarding changes to be answered
     no without user intervention.


     −R, −−root CHROOT_DIR
     Apply changes in the CHROOT_DIR directory and use the
     configuration files from the CHROOT_DIR directory.

     −s, −−sort
     Sort entries in /etc/group and /etc/gshadow by GID.

     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:

     Maximum members per group entry. When the maximum is
     reached, a new group entry (line) is started in
     /etc/group (with the same name, same password, and same

     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

     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.

     Group account information.

     Secure group account information.

     User account information.

     The grpck command exits with the following values:



     invalid command syntax

     one or more bad group entries

     can't open group files

     can't lock group files

     can't update group files

     group(5), groupmod(8), gshadow(5), passwd(5), pwck(8),