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 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, SHA256, SHA512, YESCRYPT and
	   NONE if your libc supports 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. Only absolute paths are
	   supported.

       -P, --prefix PREFIX_DIR
	   Apply changes to configuration files under the root filesystem
	   found under the directory PREFIX_DIR. This option does not chroot
	   and is intended for preparing a cross-compilation target. Some
	   limitations: NIS and LDAP users/groups are not verified. PAM
	   authentication is using the host files. No SELINUX support.

       -s, --sha-rounds ROUNDS
	   Use the specified number of rounds to encrypt the passwords.

	   You can only use this option with crypt method: SHA256 SHA512
	   YESCRYPT

	   By default, the number of rounds for SHA256 or SHA512 is defined by
	   the SHA_CRYPT_MIN_ROUNDS and SHA_CRYPT_MAX_ROUNDS variables in
	   /etc/login.defs.

	   A minimal value of 1000 and a maximal value of 999,999,999 will be
	   enforced for SHA256 and SHA512. The default number of rounds is
	   5000.

	   By default, the number of rounds for YESCRYPT is defined by the
	   YESCRYPT_COST_FACTOR in /etc/login.defs.

	   A minimal value of 1 and a maximal value of 11 will be enforced for
	   YESCRYPT. The default number of rounds is 5.

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 force 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.

       YESCRYPT_COST_FACTOR (number)
	   When ENCRYPT_METHOD is set to YESCRYPT, this defines the cost
	   factor used by the encryption algorithm by default (when the cost
	   factor is not specified on the command line).

	   With a high cost factor, it is more difficult to brute force the
	   password. But note also that more CPU resources will be needed to
	   authenticate users.

	   The value must be inside the 1-11 range.

	   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).

shadow-utils 4.18.0		  06/27/2025			   CHPASSWD(8)