centos man page for gpasswd

GPASSWD(1)							   User Commands							GPASSWD(1)

NAME
       gpasswd - administer /etc/group and /etc/gshadow

SYNOPSIS
       gpasswd [option] group

DESCRIPTION
       The gpasswd command is used to administer /etc/group, and /etc/gshadow. Every group can have administrators, members and a password.

       System administrators can use the -A option to define group administrator(s) and the -M option to define members. They have all rights of
       group administrators and members.

       gpasswd called by a group administrator with a group name only prompts for the new password of the group.

       If a password is set the members can still use newgrp(1) without a password, and non-members must supply the password.

   Notes about group passwords
       Group passwords are an inherent security problem since more than one person is permitted to know the password. However, groups are a useful
       tool for permitting co-operation between different users.

OPTIONS
       Except for the -A and -M options, the options cannot be combined.

       The options which apply to the gpasswd command are:

       -a, --add user
	   Add the user to the named group.

       -d, --delete user
	   Remove the user from the named group.

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

       -Q, --root CHROOT_DIR
	   Apply changes in the CHROOT_DIR directory and use the configuration files from the CHROOT_DIR directory.

       -r, --remove-password
	   Remove the password from the named group. The group password will be empty. Only group members will be allowed to use newgrp to join
	   the named group.

       -R, --restrict
	   Restrict the access to the named group. The group password is set to "!". Only group members with a password will be allowed to use
	   newgrp to join the named group.

       -A, --administrators user,...
	   Set the list of administrative users.

       -M, --members user,...
	   Set the list of group members.

CAVEATS
       This tool only operates on the /etc/group and /etc/gshadow files.  Thus you cannot change any NIS or LDAP group. This must be performed on
       the corresponding server.

CONFIGURATION
       The following configuration variables in /etc/login.defs change the behavior of this tool:

       ENCRYPT_METHOD (string)
	   This defines the system default encryption algorithm for encrypting passwords (if no algorithm are specified on the command line).

	   It can take one of these values: DES (default), MD5, SHA256, SHA512.

	   Note: this parameter overrides the MD5_CRYPT_ENAB variable.

       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.

       MD5_CRYPT_ENAB (boolean)
	   Indicate if passwords must be encrypted using the MD5-based algorithm. If set to yes, new passwords will be encrypted using the
	   MD5-based algorithm compatible with the one used by recent releases of FreeBSD. It supports passwords of unlimited length and longer
	   salt strings. Set to no if you need to copy encrypted passwords to other systems which don't understand the new algorithm. Default is
	   no.

	   This variable is superseded by the ENCRYPT_METHOD variable or by any command line option used to configure the encryption algorithm.

	   This variable is deprecated. You should use ENCRYPT_METHOD.

       SHA_CRYPT_MIN_ROUNDS (number), SHA_CRYPT_MAX_ROUNDS (number)
	   When ENCRYPT_METHOD is set to SHA256 or SHA512, this defines the number of SHA rounds used by the encryption algorithm by default (when
	   the number of rounds is not specified on the command line).

	   With a lot of rounds, it is more difficult to brute forcing the password. But note also that more CPU resources will be needed to
	   authenticate users.

	   If not specified, the libc will choose the default number of rounds (5000).

	   The values must be inside the 1000-999,999,999 range.

	   If only one of the SHA_CRYPT_MIN_ROUNDS or SHA_CRYPT_MAX_ROUNDS values is set, then this value will be used.

	   If SHA_CRYPT_MIN_ROUNDS > SHA_CRYPT_MAX_ROUNDS, the highest value will be used.

FILES
       /etc/group
	   Group account information.

       /etc/gshadow
	   Secure group account information.

SEE ALSO
       newgrp(1), groupadd(8), groupdel(8), groupmod(8), grpck(8), group(5), gshadow(5).

shadow-utils 4.1.5.1						    05/25/2012								GPASSWD(1)