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GPASSWD(1)                       User Commands                      GPASSWD(1)

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

       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 administrator can use the -A option to define group
       administrator(s) and the -M option to define members and has 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 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 user
           Add the user to the named group.

       -d user
           Remove the user from the named group.

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

           Restrict the access to the named group. Only group members will be
           allowed to use newgrp to join the named group.

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

       -M 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.

               Note: if you use PAM, it is recommended to set this variable
               consistently with the PAM modules configuration.

       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

           This variable is superceded 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.

           Note: if you use PAM, it is recommended to set this variable
           consistently with the PAM modules configuration.

           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

           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.

           If SHA_CRYPT_MIN_ROUNDS > SHA_CRYPT_MAX_ROUNDS, the highest 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                     11/14/2009                        GPASSWD(1)