Linux 2.6 - man page for grpck (linux section 8)
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GRPCK(8) System Management Commands GRPCK(8)
grpck - verify integrity of group files
grpck [-r] [group [ shadow ]]
grpck [-s] [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
Checks are made to verify that each entry has:
o the correct number of fields
o a unique and valid group name
o a valid group identifier (/etc/group only)
o a valid list of members and administrators
o a corresponding entry in the /etc/gshadow file (respectively /etc/group for the
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 options which apply to the grpck command are:
Execute the grpck command in read-only mode. This causes all questions regarding
changes to be answered no without user intervention.
Sort entries in /etc/group and /etc/gshadow by GID.
By default, grpck operates on /etc/groupand /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 GID).
The default value is 0, meaning that there are no limits in the number of members in a
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), shadow(5).
System Management Commands 06/24/2011 GRPCK(8)
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