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       -r, --remove-password
42           Remove the password from the named group. Only group members will
43           be allowed to use newgrp to join the named group.
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45       -R, --restrict
46           Restrict the access to the named group. Only group members will be
47           allowed to use newgrp to join the named group.
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49       -A, --administrators user,...
50           Set the list of administrative users.
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52       -M, --members user,...
53           Set the list of group members.
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CAVEATS

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

61       The following configuration variables in /etc/login.defs change the
62       behavior of this tool:
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64       ENCRYPT_METHOD (string)
65           This defines the system default encryption algorithm for encrypting
66           passwords (if no algorithm are specified on the command line).
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68           It can take one of these values:
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70           ·   DES (default)
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72           ·   MD5
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74           ·   SHA256
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76           ·   SHA512
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78               Note: this parameter overrides the MD5_CRYPT_ENAB variable.
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80           MAX_MEMBERS_PER_GROUP (number)
81               Maximum members per group entry. When the maximum is reached, a
82               new group entry (line) is started in /etc/group (with the same
83               name, same password, and same GID).
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85               The default value is 0, meaning that there are no limits in the
86               number of members in a group.
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88               This feature (split group) permits to limit the length of lines
89               in the group file. This is useful to make sure that lines for
90               NIS groups are not larger than 1024 characters.
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92               If you need to enforce such limit, you can use 25.
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94               Note: split groups may not be supported by all tools (even in
95               the Shadow toolsuite). You should not use this variable unless
96               you really need it.
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98           MD5_CRYPT_ENAB (boolean)
99               Indicate if passwords must be encrypted using the MD5-based
100               algorithm. If set to yes, new passwords will be encrypted using
101               the MD5-based algorithm compatible with the one used by recent
102               releases of FreeBSD. It supports passwords of unlimited length
103               and longer salt strings. Set to no if you need to copy
104               encrypted passwords to other systems which don´t understand the
105               new algorithm. Default is no.
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107               This variable is superceded by the ENCRYPT_METHOD variable or
108               by any command line option used to configure the encryption
109               algorithm.
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111               This variable is deprecated. You should use ENCRYPT_METHOD.
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113           SHA_CRYPT_MIN_ROUNDS (number), SHA_CRYPT_MAX_ROUNDS (number)
114               When ENCRYPT_METHOD is set to SHA256 or SHA512, this defines
115               the number of SHA rounds used by the encryption algorithm by
116               default (when the number of rounds is not specified on the
117               command line).
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119               With a lot of rounds, it is more difficult to brute forcing the
120               password. But note also that more CPU resources will be needed
121               to authenticate users.
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123               If not specified, the libc will choose the default number of
124               rounds (5000).
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126               The values must be inside the 1000-999999999 range.
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128               If only one of the SHA_CRYPT_MIN_ROUNDS or SHA_CRYPT_MAX_ROUNDS
129               values is set, then this value will be used.
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131               If SHA_CRYPT_MIN_ROUNDS > SHA_CRYPT_MAX_ROUNDS, the highest
132               value will be used.
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FILES

135       /etc/group
136           Group account information.
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138       /etc/gshadow
139           Secure group account information.
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