chpasswd man page on Mandriva

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CHPASSWD(8)		  System Management Commands		   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 supplied password must be in clear-text, and is
       encrypted by chpasswd. Also the password age will be updated, if
       present.

       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.

OPTIONS
       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).

	   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.

	   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
	       algorithm.

	       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.

	       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.

FILES
       /etc/passwd
	   User account information.

       /etc/shadow
	   Secure user account information.

       /etc/login.defs
	   Shadow password suite configuration.

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

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