|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | SYNOPSIS | DESCRIPTION | OPTIONS | CAVEATS | CONFIGURATION | FILES | SEE ALSO | COLOPHON |
|
|
|
GPASSWD(1) User Commands GPASSWD(1)
gpasswd - administer /etc/group and /etc/gshadow
gpasswd [option] group
The gpasswd command is used to administer /etc/group, and
/etc/gshadow. Every group can have administrators, members and a
password.
System administrators can use the -A option to define group
administrator(s) and the -M option to define members. They have
all rights of group administrators and members.
gpasswd called by a group administrator with a group name only
prompts for the new password of the group.
If a password is set the members can still use newgrp(1) without
a password, and non-members must supply the password.
Notes about group passwords
Group passwords are an inherent security problem since more than
one person is permitted to know the password. However, groups are
a useful tool for permitting co-operation between different
users.
Except for the -A and -M options, the options cannot be combined.
The options which apply to the gpasswd command are:
-a, --add user
Add the user to the named group.
-d, --delete user
Remove the user from the named group.
-h, --help
Display help message and exit.
-Q, --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.
-r, --remove-password
Remove the password from the named group. The group password
will be empty. Only group members will be allowed to use
newgrp to join the named group.
-R, --restrict
Restrict the access to the named group. The group password is
set to "!". Only group members with a password will be
allowed to use newgrp to join the named group.
-A, --administrators user,...
Set the list of administrative users.
-M, --members user,...
Set the list of group members.
This tool only operates on the /etc/group and /etc/gshadow files.
Thus you cannot change any NIS or LDAP group. This must be
performed on the corresponding server.
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 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.
/etc/group
Group account information.
/etc/gshadow
Secure group account information.
newgrp(1), groupadd(8), groupdel(8), groupmod(8), grpck(8),
group(5), gshadow(5).
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 2024-06-15. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-13.) 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 4.14.0 06/15/2024 GPASSWD(1)
Pages that refer to this page: newgrp(1), sg(1), group(5), chgpasswd(8)
|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|