gpasswd(1)

1GPASSWD(1)                       User Commands                      GPASSWD(1)
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NAME

6       gpasswd - administer /etc/group and /etc/gshadow
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SYNOPSIS

9       gpasswd [option] group
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DESCRIPTION

12       The gpasswd command is used to administer /etc/group, and /etc/gshadow.
13       Every group can have administrators, members and a password.
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15       System administrators can use the -A option to define group
16       administrator(s) and the -M option to define members. They have all
17       rights of group administrators and members.
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19       gpasswd called by a group administrator with a group name only prompts
20       for the new password of the group.
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22       If a password is set the members can still use newgrp(1) without a
23       password, and non-members must supply the password.
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25   Notes about group passwords
26       Group passwords are an inherent security problem since more than one
27       person is permitted to know the password. However, groups are a useful
28       tool for permitting co-operation between different users.
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OPTIONS

31       Except for the -A and -M options, the options cannot be combined.
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33       The options which apply to the gpasswd command are:
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35       -a, --add user
36           Add the user to the named group.
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38       -d, --delete user
39           Remove the user from the named group.
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41       -h, --help
42           Display help message and exit.
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44       -Q, --root CHROOT_DIR
45           Apply changes in the CHROOT_DIR directory and use the configuration
46           files from the CHROOT_DIR directory.
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48       -r, --remove-password
49           Remove the password from the named group. The group password will
50           be empty. Only group members will be allowed to use newgrp to join
51           the named group.
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53       -R, --restrict
54           Restrict the access to the named group. The group password is set
55           to "!". Only group members with a password will be allowed to use
56           newgrp to join the named group.
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58       -A, --administrators user,...
59           Set the list of administrative users.
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61       -M, --members user,...
62           Set the list of group members.
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CAVEATS

65       This tool only operates on the /etc/group and /etc/gshadow files.  Thus
66       you cannot change any NIS or LDAP group. This must be performed on the
67       corresponding server.
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CONFIGURATION

70       The following configuration variables in /etc/login.defs change the
71       behavior of this tool:
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73       ENCRYPT_METHOD (string)
74           This defines the system default encryption algorithm for encrypting
75           passwords (if no algorithm are specified on the command line).
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77           It can take one of these values: DES (default), MD5, SHA256,
78           SHA512. MD5 and DES should not be used for new hashes, see crypt(5)
79           for recommendations.
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81           Note: this parameter overrides the MD5_CRYPT_ENAB variable.
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83       MAX_MEMBERS_PER_GROUP (number)
84           Maximum members per group entry. When the maximum is reached, a new
85           group entry (line) is started in /etc/group (with the same name,
86           same password, and same GID).
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88           The default value is 0, meaning that there are no limits in the
89           number of members in a group.
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91           This feature (split group) permits to limit the length of lines in
92           the group file. This is useful to make sure that lines for NIS
93           groups are not larger than 1024 characters.
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95           If you need to enforce such limit, you can use 25.
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97           Note: split groups may not be supported by all tools (even in the
98           Shadow toolsuite). You should not use this variable unless you
99           really need it.
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101       MD5_CRYPT_ENAB (boolean)
102           Indicate if passwords must be encrypted using the MD5-based
103           algorithm. If set to yes, new passwords will be encrypted using the
104           MD5-based algorithm compatible with the one used by recent releases
105           of FreeBSD. It supports passwords of unlimited length and longer
106           salt strings. Set to no if you need to copy encrypted passwords to
107           other systems which don't understand the new algorithm. Default is
108           no.
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110           This variable is superseded by the ENCRYPT_METHOD variable or by
111           any command line option used to configure the encryption algorithm.
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113           This variable is deprecated. You should use ENCRYPT_METHOD.
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115       SHA_CRYPT_MIN_ROUNDS (number), SHA_CRYPT_MAX_ROUNDS (number)
116           When ENCRYPT_METHOD is set to SHA256 or SHA512, this defines the
117           number of SHA rounds used by the encryption algorithm by default
118           (when the number of rounds is not specified on the command line).
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120           With a lot of rounds, it is more difficult to brute forcing the
121           password. But note also that more CPU resources will be needed to
122           authenticate users.
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124           If not specified, the libc will choose the default number of rounds
125           (5000), which is orders of magnitude too low for modern hardware.
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127           The values must be inside the 1000-999,999,999 range.
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129           If only one of the SHA_CRYPT_MIN_ROUNDS or SHA_CRYPT_MAX_ROUNDS
130           values is set, then this value will be used.
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132           If SHA_CRYPT_MIN_ROUNDS > SHA_CRYPT_MAX_ROUNDS, the highest value
133           will be used.
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FILES

136       /etc/group
137           Group account information.
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139       /etc/gshadow
140           Secure group account information.
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