Provided by: passwd_4.2-3.1ubuntu5_i386 bug

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 overwiten 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.

       -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.

           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).

           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).