chpasswd(8)

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.

   -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).

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