chpasswd
update passwords in batch mode
see also :
passwd - newusers - useradd
Synopsis
add an example, a script, a trick and tips
examples
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
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 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.
options
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.
-e,
--encrypted
Supplied passwords are in
encrypted form.
-S,
--stdout
Report encrypted passwords to
stdout instead of updating password file.
-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.
-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 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.
configuration
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
authenticate users.
If not specified, the libc will choose the default number of
rounds (5000).
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.
files
/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.
see also
passwd ,
newusers , login.defs,
useradd .