CHGPASSWD(8) System Management Commands CHGPASSWD(8)
NAME
chgpasswd - update group passwords in batch mode
SYNOPSIS
chgpasswd [options]
DESCRIPTION
The chgpasswd command reads a list of group name and password pairs from
standard input and uses this information to update a set of existing
groups. Each line is of the format:
group_name:password
By default the supplied password must be in clear-text, and is encrypted
by chgpasswd.
The default encryption algorithm can be defined for the system with the
ENCRYPT_METHOD variable of /etc/login.defs, and can be overwritten with
the -e, -m, or -c options.
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 chgpasswd command are:
-c, --crypt-method
Use the specified method to encrypt the passwords.
The available methods are DES, MD5, SHA256, SHA512, YESCRYPT and
NONE if your libc supports 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.
-R, --root CHROOT_DIR
Apply changes in the CHROOT_DIR directory and use the configuration
files from the CHROOT_DIR directory. Only absolute paths are
supported.
-s, --sha-rounds
Use the specified number of rounds to encrypt the passwords.
You can only use this option with crypt method: SHA256 SHA512
YESCRYPT
By default, the number of rounds for SHA256 or SHA512 is defined by
the SHA_CRYPT_MIN_ROUNDS and SHA_CRYPT_MAX_ROUNDS variables in
/etc/login.defs.
A minimal value of 1000 and a maximal value of 999,999,999 will be
enforced for SHA256 and SHA512. The default number of rounds is
5000.
By default, the number of rounds for YESCRYPT is defined by the
YESCRYPT_COST_FACTOR in /etc/login.defs.
A minimal value of 1 and a maximal value of 11 will be enforced for
YESCRYPT. The default number of rounds is 5.
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,
YESCRYPT. MD5 and DES should not be used for new hashes, see
crypt(5) for recommendations.
Note: this parameter overrides the MD5_CRYPT_ENAB variable.
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.
MAX_MEMBERS_PER_GROUP (number)
Maximum members per group entry. When the maximum is reached, a new
group entry (line) is started in /etc/group (with the same name,
same password, and same GID).
The default value is 0, meaning that there are no limits in the
number of members in a group.
This feature (split group) permits to limit the length of lines in
the group file. This is useful to make sure that lines for NIS
groups are not larger than 1024 characters.
If you need to enforce such limit, you can use 25.
Note: split groups may not be supported by all tools (even in the
Shadow toolsuite). You should not use this variable unless you
really need it.
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 superseded 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.
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.
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 force 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), which is orders of magnitude too low for modern hardware.
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.
YESCRYPT_COST_FACTOR (number)
When ENCRYPT_METHOD is set to YESCRYPT, this defines the cost factor
used by the encryption algorithm by default (when the cost factor is
not specified on the command line).
With a high cost factor, it is more difficult to brute force the
password. But note also that more CPU resources will be needed to
authenticate users.
The value must be inside the 1-11 range.
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/group
Group account information.
/etc/gshadow
Secure group account information.
/etc/login.defs
Shadow password suite configuration.
SEE ALSO
gpasswd(1), groupadd(8), login.defs(5).
shadow-utils 4.17.4 04/19/2025 CHGPASSWD(8)
Generated by dwww version 1.16 on Tue Dec 16 07:29:40 CET 2025.