chgpasswd - Man Page

chgpasswd [options]

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.

The options which apply to the chgpasswd command are:

-c,  --crypt-method

Use the specified method to encrypt the passwords.

The available methods are BCRYPT, 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: BCRYPT SHA256 SHA512 YESCRYPT

By default, the number of rounds for BCRYPT is defined by the BCRYPT_MIN_ROUNDS and BCRYPT_MAX_ROUNDS variables in /etc/login.defs.

A minimal value of 4 and a maximal value of 31 will be enforced for BCRYPT. The default number of rounds is 13.

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.

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.

The following configuration variables in /etc/login.defs change the behavior of this tool:

BCRYPT_MIN_ROUNDS (number), BCRYPT_MAX_ROUNDS (number)

When ENCRYPT_METHOD is set to BCRYPT, this defines the number of BCRYPT 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.

The values must be inside the 4-31 range.

If only one of the BCRYPT_MIN_ROUNDS or BCRYPT_MAX_ROUNDS values is set, then this value will be used.

If BCRYPT_MIN_ROUNDS > BCRYPT_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.

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: BCRYPT, 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.

/etc/group

Group account information.

/etc/gshadow

Secure group account information.

/etc/login.defs

Shadow password suite configuration.

gpasswd(1), groupadd(8), login.defs(5).