chgpasswd man page on ElementaryOS

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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 overwiten 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, NONE, and SHA256 or SHA512 if
	   your libc support 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.

       -s, --sha-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.

       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.

	   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 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/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 4.1.5.1		  02/17/2014			  CHGPASSWD(8)
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