CHGPASSWD(8)              (02/07/2020)               CHGPASSWD(8)

     NAME
          chgpasswd - update group passwords in batch mode

     SYNOPSIS
          chgpasswd [options]

     DESCRIPTION
          The chgpasswd command reads a list of group name and
          password pairs from standard input and uses this information
          to update a set of existing groups. Each line is of the
          format:

          group_name:password

          By default the supplied password must be in clear-text, and
          is encrypted by chgpasswd.

          The default encryption algorithm can be defined for the
          system with the ENCRYPT_METHOD variable of /etc/login.defs,
          and can be overwritten with the -e, -m, or -c options.

          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 chgpasswd command are:

          -c, --crypt-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.

          -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
              Use the specified number of rounds to encrypt the

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              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.

          You should make sure the passwords and the encryption method
          respect the system's password policy.

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

          ENCRYPT_METHOD (string)
              This defines the system default encryption algorithm for
              encrypting passwords (if no algorithm are specified on
              the command line).

              It can take one of these values: DES (default), MD5,
              SHA256, SHA512.

              Note: this parameter overrides the MD5_CRYPT_ENAB
              variable.

              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.

          MAX_MEMBERS_PER_GROUP (number)
              Maximum members per group entry. When the maximum is
              reached, a new group entry (line) is started in
              /etc/group (with the same name, same password, and same
              GID).

              The default value is 0, meaning that there are no limits
              in the number of members in a group.

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              This feature (split group) permits to limit the length
              of lines in the group file. This is useful to make sure
              that lines for NIS groups are not larger than 1024
              characters.

              If you need to enforce such limit, you can use 25.

              Note: split groups may not be supported by all tools
              (even in the Shadow toolsuite). You should not use this
              variable unless you really need it.

          MD5_CRYPT_ENAB (boolean)
              Indicate if passwords must be encrypted using the
              MD5-based algorithm. If set to yes, new passwords will
              be encrypted using the MD5-based algorithm compatible
              with the one used by recent releases of FreeBSD. It
              supports passwords of unlimited length and longer salt
              strings. Set to no if you need to copy encrypted
              passwords to other systems which don't understand the
              new algorithm. Default is no.

              This variable is superseded by the ENCRYPT_METHOD
              variable or by any command line option used to configure
              the encryption algorithm.

              This variable is deprecated. You should use
              ENCRYPT_METHOD.

              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.

          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.

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              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/group
              Group account information.

          /etc/gshadow
              Secure group account information.

          /etc/login.defs
              Shadow password suite configuration.

     SEE ALSO
          gpasswd(1), groupadd(8), login.defs(5).

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