CHPASSWD(8) System Management Commands CHPASSWD(8)NAMEchpasswd - update passwords in batch mode
SYNOPSISchpasswd [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 supplied password must be in clear-text, and is
encrypted by chpasswd. Also the password age will be updated, if
present.
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.
OPTIONS
The options which apply to the chpasswd command are:
-c, --crypt-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.
-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.
-s, --sha-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 be
enforced.
You can only use this option with the SHA256 or SHA512 crypt
method.
By default, the number of rounds is defined by the
SHA_CRYPT_MIN_ROUNDS and SHA_CRYPT_MAX_ROUNDS variables in
/etc/login.defs.
CAVEATS
Remember to set permissions or umask to prevent readability of
unencrypted files by other users.
You should make sure the passwords and the encryption method respect
the system´s password policy.
CONFIGURATION
The following configuration variables in /etc/login.defs change the
behavior of this tool:
ENCRYPT_METHOD (string)
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)
· MD5
· SHA256
· SHA512
Note: this parameter overrides the MD5_CRYPT_ENAB variable.
MD5_CRYPT_ENAB (boolean)
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
algorithm.
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
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 authenticate users.
If not specified, the libc will choose the default number of
rounds (5000).
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.
FILES
/etc/passwd
User account information.
/etc/shadow
Secure user account information.
/etc/login.defs
Shadow password suite configuration.
SEE ALSOpasswd(1), newusers(8), login.defs(5), useradd(8).
System Management Commands 07/24/2009 CHPASSWD(8)