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 passwords must be supplied in clear-text, and are
encrypted by chpasswd. Also the password age will be updated, if
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, NONE, and SHA256 or SHA512 if
your libc support these methods.
By default, PAM is used to encrypt the passwords.
Supplied passwords are in encrypted form.
Display help message and exit.
Use MD5 encryption instead of DES when the supplied passwords are
-R, --root CHROOT_DIR
Apply changes in the CHROOT_DIR directory and use the
configuration files from the CHROOT_DIR directory.
-s, --sha-rounds 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
You can only use this option with the SHA256 or SHA512 crypt
By default, the number of rounds is defined by the
SHA_CRYPT_MIN_ROUNDS and SHA_CRYPT_MAX_ROUNDS variables in
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 forcing the
password. But note also that more CPU resources will be needed to
If not specified, the libc will choose the default number of
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.
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 ⟨http://pkg-shadow.alioth.debian.org/⟩. If
you have a bug report for this manual page, see
⟨http://pkg-shadow.alioth.debian.org/getinvolved.php⟩. This page was
obtained from the project's upstream Git repository
⟨git://anonscm.debian.org/git/pkg-shadow/shadow.git⟩ on 2017-03-13.
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 firstname.lastname@example.org
shadow-utils 4.4 02/18/2017 CHPASSWD(8)