chpasswd(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | CAVEATS | CONFIGURATION | FILES | SEE ALSO | COLOPHON

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:

       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 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
           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         top

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

CONFIGURATION         top

       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), 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         top

       /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         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 
       ⟨https://github.com/shadow-maint/shadow⟩.  If you have a bug
       report for this manual page, send it to
       pkg-shadow-devel@alioth-lists.debian.net.  This page was obtained
       from the project's upstream Git repository
       ⟨https://github.com/shadow-maint/shadow⟩ on 2021-08-27.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-08-14.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better 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
       man-pages@man7.org

shadow-utils 4.8.1             08/27/2021                    CHPASSWD(8)

Pages that refer to this page: passwd(1)