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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 supplied password must be in clear-text, and is
encrypted by chpasswd. Also the password age will be updated, if
The default encryption algorithm can be defined for the system with the
ENCRYPT_METHOD variable of /etc/login.defs, and can be overwiten with
the -e, -m, or -c options.
chpasswd first update the password in memory, and then commit all the
changes to disk if no errors occured for any users.
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:
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.
Supplied passwords are in encrypted form.
Display help message and exit.
Use MD5 encryption instead of DES when the supplied passwords are
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).
You should make sure the passwords and the encryption method respect
the system?s password policy.
The following configuration variables in /etc/login.defs change the
behavior of this tool:
This defines the system default encryption algorithm for encrypting
passwords (if no algorithm are specified on the command line).
It can take one of these values:
? DES (default)
Note: this parameter overrides the MD5_CRYPT_ENAB variable.
Indicate if passwords must be encrypted using the MD5-based
algorithm. If set to yes, new passwords will be encrypted using
the MD5-based algorithm compatible with the one used by recent
releases of FreeBSD. It supports passwords of unlimited length
and longer salt strings. Set to no if you need to copy
encrypted passwords to other systems which don?t understand the
new algorithm. Default is no.
This variable is superceded by the ENCRYPT_METHOD variable or
by any command line option used to configure the encryption
This variable is deprecated. You should use ENCRYPT_METHOD.
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
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 authenticate users.
If not specified, the libc will choose the default number of
The values must be inside the 1000-999999999 range.
Shadow password suite configuration.
passwd(1), newusers(8), login.defs(5), useradd(8).
System Management Commands 07/24/2009 CHPASSWD(8)