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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | CAVEATS | CONFIGURATION | FILES | SEE ALSO | COLOPHON |
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CHPASSWD(8) System Management Commands CHPASSWD(8)
chpasswd - update passwords in batch mode
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:
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.
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 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
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.
Remember to set permissions or umask to prevent readability of
unencrypted files by other users.
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.
/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.
passwd(1), newusers(8), login.defs(5), useradd(8).
This page is part of the shadow-utils (utilities for managing
accounts and shadow password files) project. Information about
the project can be found at
⟨https://github.com/shadow-maint/shadow⟩. If you have a bug report
for this manual page, send it to
[email protected]. This page was obtained
from the project's upstream Git repository
⟨https://github.com/shadow-maint/shadow⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-10.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
shadow-utils 4.18.0 08/11/2025 CHPASSWD(8)
Pages that refer to this page: passwd(1)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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