gpasswd manpage

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GPASSWD(1)			 User Commands			    GPASSWD(1)

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

       gpasswd [option] group

       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.

       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.

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

       -R, --restrict
	   Restrict the access to the named group. Only group members 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.

       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.

       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:

	   o   DES (default)

	   o   MD5

	   o   SHA256

	   o   SHA512

	       Note: this parameter overrides the MD5_CRYPT_ENAB variable.

	       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 superceded by the ENCRYPT_METHOD variable or
	       by any command line option used to configure the encryption

	       This variable is deprecated. You should use ENCRYPT_METHOD.

	       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 1000-999999999 range.

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

	       value will be used.

	   Group account information.

	   Secure group account information.

       newgrp(1), groupadd(8), groupdel(8), groupmod(8), grpck(8), group(5),

User Commands			  07/24/2009			    GPASSWD(1)