chgpasswd(8) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | CAVEATS | CONFIGURATION | FILES | SEE ALSO | COLOPHON

CHGPASSWD(8)           System Management Commands           CHGPASSWD(8)

NAME         top

       chgpasswd - update group passwords in batch mode

SYNOPSIS         top

       chgpasswd [options]

DESCRIPTION         top

       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         top

       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         top

       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         top

       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. 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 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), 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.

FILES         top

       /etc/group
           Group account information.

       /etc/gshadow
           Secure group account information.

       /etc/login.defs
           Shadow password suite configuration.

SEE ALSO         top

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

COLOPHON         top

       This page is part of the shadow-utils (utilities for managing
       accounts and shadow password files) project.  Information about
       the project can be found at 
       ⟨https://github.com/shadow-maint/shadow⟩.  If you have a bug
       report for this manual page, send it to
       pkg-shadow-devel@alioth-lists.debian.net.  This page was obtained
       from the project's upstream Git repository
       ⟨https://github.com/shadow-maint/shadow⟩ on 2021-08-27.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-08-14.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

shadow-utils 4.8.1             08/27/2021                   CHGPASSWD(8)