NAME
gpasswd - administer /etc/group and /etc/gshadow
SYNOPSIS
gpasswd [option] group
DESCRIPTION
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.
OPTIONS
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.
-r, --remove-password
Remove the password from the named group. Only group members will
be allowed to use newgrp to join the named group.
-R, --restrict
Restrict the access to the named group. Only group members 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.
CAVEATS
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.
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:
o DES (default)
o MD5
o SHA256
o 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 dont understand the new algorithm. Default is
no.
This variable is superceded 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 1000-999999999 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.
SEE ALSO
newgrp(1), groupadd(8), groupdel(8), groupmod(8), grpck(8), group(5),
gshadow(5).