GPASSWD(1)

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

SYNOPSIS

gpasswd [option] groupe

DESCRIPTION

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 sur les mots de passe de groupe

Les mots de passe de groupe représentent naturellement un risque en matière de sécurité, puisque plusieurs personnes ont connaissance du mot de passe. Cependant, les groupes sont utiles pour permettre la coopération entre différents utilisateurs.

OPTIONS

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

The options which apply to the gpasswd command are:

-a utilisateur
    Add the user to the named group.

-d utilisateur
    Remove the user from the named group.

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

-R
    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.

AVERTISSEMENTS

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.

        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 no.

    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.

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 1000-999999999 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.

FICHIERS

/etc/group
    Informations sur les groupes.

/etc/gshadow
    Informations sécurisées sur les groupes.

VOIR AUSSI

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