groupmod(8) [linux man page]
GROUPMOD(8) System Management Commands GROUPMOD(8) NAME
groupmod - modify a group definition on the system SYNOPSIS
groupmod [options] GROUP DESCRIPTION
The groupmod command modifies the definition of the specified GROUP by modifying the appropriate entry in the group database. OPTIONS
The options which apply to the groupmod command are: -g, --gid GID The group ID of the given GROUP will be changed to 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. -h, --help Display help message and exit. -n, --new-name NEW_GROUP The name of the group will be changed from GROUP to NEW_GROUP name. -o, --non-unique When used with the -g option, allow to change the group GID to a non-unique value. -p, --password PASSWORD The encrypted password, as returned by crypt(3). 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. CONFIGURATION
The following configuration variables in /etc/login.defs change the behavior of this tool: MAX_MEMBERS_PER_GROUP (number) 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 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. FILES
/etc/group Group account information. /etc/gshadow Secure group account information. EXIT VALUES
The groupmod command exits with the following values: 0 success 2 invalid command syntax 3 invalid argument to option 4 specified group doesn't exist 6 specified group doesn't exist 9 group name already in use 10 can't update group file SEE ALSO
chfn(1), chsh(1), passwd(1), gpasswd(8), groupadd(8), groupdel(8), useradd(8), userdel(8), usermod(8). System Management Commands 06/24/2011 GROUPMOD(8)
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GRPCK(8) System Management Commands GRPCK(8) NAME
grpck - verify integrity of group files SYNOPSIS
grpck [-r] [group [ shadow ]] grpck [-s] [group [ shadow ]] DESCRIPTION
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: 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 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. OPTIONS
The options which apply to the grpck command are: -r Execute the grpck command in read-only mode. This causes all questions regarding changes to be answered no without user intervention. -s 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. CONFIGURATION
The following configuration variables in /etc/login.defs change the behavior of this tool: MAX_MEMBERS_PER_GROUP (number) 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 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. FILES
/etc/group Group account information. /etc/gshadow Secure group account information. /etc/passwd User account information. EXIT VALUES
The grpck command exits with the following values: 0 success 1 invalid command syntax 2 one or more bad group entries 3 can't open group files 4 can't lock group files 5 can't update group files SEE ALSO
group(5), groupmod(8), gshadow(5), passwd(5), pwck(8), shadow(5). System Management Commands 06/24/2011 GRPCK(8)