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 4.17.4 04/19/2025 CHPASSWD(8)
Generated by dwww version 1.16 on Tue Dec 16 04:28:21 CET 2025.