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 occured 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.
Report encrypted passwords to stdout instead of updating password
Display help message and exit.
Use MD5 encryption instead of DES when the supplied passwords are
By default, the number of rounds is defined by the
SHA_CRYPT_MIN_ROUNDS and SHA_CRYPT_MAX_ROUNDS variables in
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 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 rounds
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.
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.
User account information.
Secure user account information.
Shadow password suite configuration.
PAM configuration for chpasswd.
passwd(1), newusers(8), login.defs(5), useradd(8).
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