NAME

       chpasswd - update passwords in batch mode

SYNOPSIS

       chpasswd [options]

DESCRIPTION

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

       user_name:password

       By default the passwords must be supplied in clear-text, and are encrypted by chpasswd. Also the password
       age will be updated, if present.

       By default, passwords are encrypted by PAM, but (even if not recommended) you can select a different
       encryption method with the -e, -m, or -c options.

       Except when PAM is used to encrypt the passwords,chpasswd first updates all the passwords in memory, and
       then commits all the changes to disk if no errors occured for any user.

       When PAM is used to encrypt the passwords (and update the passwords in the system database) then if a
       password cannot be updated chpasswd continues updating the passwords of the next users, and will return
       an error code on exit.

       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 chpasswd command are:

       -c, --crypt-method 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.

           By default, PAM is used to encrypt the passwords.

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

       -S, --stdout
           Report encrypted passwords to stdout instead of updating password file.

       -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 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.

CONFIGURATION

       The following configuration variables in /etc/login.defs change the behavior of this tool:

       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/passwd
           User account information.

       /etc/shadow
           Secure user account information.

       /etc/login.defs
           Shadow password suite configuration.

       /etc/pam.d/chpasswd
           PAM configuration for chpasswd.

SEE ALSO

       passwd(1), newusers(8), login.defs(5),useradd(8).