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CHPASSWD(8) | System Management Commands | CHPASSWD(8) |
NAME¶
chpasswd - update passwords in batch modeSYNOPSIS¶
chpasswd
[ 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:OPTIONS¶
The options which apply to the chpasswd command are: -c, --crypt-method METHODUse 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.
-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/passwdUser 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¶
05/25/2012 | shadow-utils 4.1.5.1 |