CHPASSWD(8)               (02/07/2020)                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 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
          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

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              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

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              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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