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           chpasswd [options]


           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 supplied password must be in clear-text, and is
           encrypted by chpasswd. Also the password age will be updated, if
           The default encryption algorithm can be defined for the system with the
           ENCRYPT_METHOD variable of /etc/login.defs, and can be overwiten with
           the -e, -m, or -c options.
           chpasswd first update the password in memory, and then commit all the
           changes to disk if no errors occured for any users.
           This command is intended to be used in a large system environment where
           many accounts are created at a single time.


           The options which apply to the chpasswd 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.
           -s, --sha-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).
           You should make sure the passwords and the encryption method respect
           the system?s password policy.


           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.
               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 superceded by the ENCRYPT_METHOD variable or
                   by any command line option used to configure the encryption
                   This variable is deprecated. You should use ENCRYPT_METHOD.
               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 1000-999999999 range.
               Shadow password suite configuration.


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

    System Management Commands 07/24/2009 CHPASSWD(8)


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