NAME

       chgpasswd - update group passwords in batch mode

SYNOPSIS

       chgpasswd [options]

DESCRIPTION

       The chgpasswd command reads a list of group name and password pairs from standard input
       and uses this information to update a set of existing groups. Each line is of the format:

       group_name:password

       By default the supplied password must be in clear-text, and is encrypted by chgpasswd.

       The default encryption algorithm can be defined for the system with the ENCRYPT_METHOD
       variable of /etc/login.defs, and can be overwritten with the -e, -m, or -c options.

       This command is intended to be used in a large system environment where many accounts are
       created at a single time.

OPTIONS

       The options which apply to the chgpasswd command are:

       -c, --crypt-method
           Use the specified method to encrypt the passwords.

           The available methods are DES, MD5, NONE, and SHA256 or SHA512 if your libc support
           these methods.

       -e, --encrypted
           Supplied passwords are in encrypted form.

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

       -m, --md5
           Use MD5 encryption instead of DES when the supplied passwords are not encrypted.

       -R, --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.

       -s, --sha-rounds
           Use the specified number of rounds to encrypt the passwords.

           The value 0 means that the system will choose the default number of rounds for the
           crypt method (5000).

           A minimal value of 1000 and a maximal value of 999,999,999 will be enforced.

           You can only use this option with the SHA256 or SHA512 crypt method.

           By default, the number of rounds is defined by the SHA_CRYPT_MIN_ROUNDS and
           SHA_CRYPT_MAX_ROUNDS variables in /etc/login.defs.

CAVEATS

       Remember to set permissions or umask to prevent readability of unencrypted files by other
       users.

       You should make sure the passwords and the encryption method respect the system's password
       policy.

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. MD5 and DES
           should not be used for new hashes, see crypt(5) for recommendations.

           Note: this parameter overrides the MD5_CRYPT_ENAB variable.

           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.

       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.

           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.

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

           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.

           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.

FILES

       /etc/group
           Group account information.

       /etc/gshadow
           Secure group account information.

       /etc/login.defs
           Shadow password suite configuration.

SEE ALSO

       gpasswd(1), groupadd(8), login.defs(5).