GPASSWD(1)

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

SINOSSI

gpasswd [option] group

DESCRIZIONE

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.

  Note sulle password di gruppo

Le password di gruppo rappresentano un intrinseco problema di sicurezza perché più di una persona deve conoscerle. Ciononostante i gruppi sono uno strumento molto utile per la cooperazione tra vari utenti.

OPZIONI

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
    Mostra un messaggio di aiuto ed esce.

-Q, --root CHROOT_DIR
    Apply changes in the CHROOT_DIR directory and use the configuration files from the CHROOT_DIR directory. Only absolute paths are supported. No SELINUX support.

-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,...
    Imposta l'elenco degli utenti amministratori.

-M, --members user,...
    Definisce l'elenco dei membri del gruppo.

AVVISI/CAVEAT

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.

CONFIGURAZIONE

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 is specified on the command line).

    It can take one of these values: SHA256, SHA512 (default), YESCRYPT. See crypt(5) for recommendations.

    Note: this only affects the generation of group passwords. The generation of user passwords is done by PAM and subject to the PAM configuration. It is recommended to set this variable consistently with the PAM configuration.

    History: This variable is used by other programs, which may still default to unsafe algorithms such as DES. To avoid using unsafe algorithms, the variable should always be specified.

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).

    Il valore predefinito è 0, che non pone nessun limite al numero di membri per gruppo.

    Questa opzione (dividi gruppo) permette di limitare la lunghezza delle righe nel file «group». Questo è utile per essere certi che le righe per gruppi NIS non eccedano i 1024 caratteri.

    Se si deve impostare questo limite, si può usare 25.

    Nota: la divisione dei gruppi potrebbe non essere supportata da ogni strumento (anche all'interno del pacchetto Shadow). Non si dovrebbe utilizzare questa variabile a meno di esserci forzati.

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 force 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), which is orders of magnitude too low for modern hardware.

    Il valore deve essere compreso tra 1.000 e 999.999.999.

    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.

    Note: this only affect the generation of group passwords. The generation of user passwords is done by PAM and subject to the PAM configuration. It is recommended to set this variable consistently with the PAM configuration.

FILE

/etc/group
    Informazioni sugli account di gruppo.

/etc/gshadow
    Informazioni sicure sugli account di gruppo.

VEDERE ANCHE

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