CHPASSWD(8)              System Management Commands              CHPASSWD(8)

NAME         top

       chpasswd - update passwords in batch mode

SYNOPSIS         top

       chpasswd [options]

DESCRIPTION         top

       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:


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

       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 occurred 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         top

       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

           By default, the number of rounds is defined by the
           SHA_CRYPT_MIN_ROUNDS and SHA_CRYPT_MAX_ROUNDS variables in

CAVEATS         top

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


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

           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         top

           User account information.

           Secure user account information.

           Shadow password suite configuration.

           PAM configuration for chpasswd.

SEE ALSO         top

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

COLOPHON         top

       This page is part of the shadow-utils (utilities for managing
       accounts and shadow password files) project.  Information about the
       project can be found at ⟨⟩.  If
       you have a bug report for this manual page, see
       ⟨⟩.  This page was
       obtained from the project's upstream Git repository
       ⟨git://⟩ on 2018-02-02.
       (At that time, the date of the most recent commit that was found in
       the repository was 2017-09-27.)  If you discover any rendering prob‐
       lems in this HTML version of the page, or you believe there is a bet‐
       ter or more up-to-date source for the page, or you have corrections
       or improvements to the information in this COLOPHON (which is not
       part of the original manual page), send a mail to

shadow-utils 4.4                 02/02/2018                      CHPASSWD(8)

Pages that refer to this page: passwd(1)