| CHGPASSWD(8) | System Management Commands | CHGPASSWD(8) |
.SH "NAME" chgpasswd - update group passwords in batch mode
.SH "SYNOPSIS"
.HP 240u
chgpasswd
[options]
.SH "DESCRIPTION"
.PP 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:
.PP group_name:password
.PP By default the supplied password must be in clear-text, and is encrypted
by chgpasswd.
.PP 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 or -c options.
.PP This command is intended to be used in a large system environment where
many accounts are created at a single time.
.SH "OPTIONS"
.PP The options which apply to the chgpasswd command are:
.PP -c, --crypt-method
Use the specified method to encrypt the passwords.
The available methods are SHA256, SHA512, YESCRYPT and NONE if your libc supports these methods.
.RE
.PP -e, --encrypted
Supplied passwords are in encrypted form.
.RE
.PP -h, --help
Display help message and exit.
.RE
.PP -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. No SELINUX support.
.RE
.PP -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.
.RE
.SH "CAVEATS"
.PP Remember to set permissions or umask to prevent readability of
unencrypted files by other users.
.PP You should make sure the passwords and the encryption method respect the
system's password policy.
.SH "CONFIGURATION"
.PP 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 is specified on the command line).
It can take one of these values: SHA256, SHA512 (default),
YESCRYPT. See crypt(5) for recommendations.
Note: this only affects 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.
History: This variable is used by other programs, which may still default to
unsafe algorithms such as DES. To avoid using unsafe algorithms, the
variable should always be specified.
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.
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.
.SH "FILES"
.PP /etc/group
Group account information.
.RE
.PP /etc/gshadow
Secure group account information.
.RE
.PP /etc/login.defs
| 10/27/2026 | shadow-utils 4.20.3 |