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.
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80           Note: this parameter overrides the MD5_CRYPT_ENAB variable.
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82       MAX_MEMBERS_PER_GROUP (number)
83           Maximum members per group entry. When the maximum is reached, a new
84           group entry (line) is started in /etc/group (with the same name,
85           same password, and same GID).
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87           The default value is 0, meaning that there are no limits in the
88           number of members in a group.
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90           This feature (split group) permits to limit the length of lines in
91           the group file. This is useful to make sure that lines for NIS
92           groups are not larger than 1024 characters.
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94           If you need to enforce such limit, you can use 25.
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96           Note: split groups may not be supported by all tools (even in the
97           Shadow toolsuite). You should not use this variable unless you
98           really need it.
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100       MD5_CRYPT_ENAB (boolean)
101           Indicate if passwords must be encrypted using the MD5-based
102           algorithm. If set to yes, new passwords will be encrypted using the
103           MD5-based algorithm compatible with the one used by recent releases
104           of FreeBSD. It supports passwords of unlimited length and longer
105           salt strings. Set to no if you need to copy encrypted passwords to
106           other systems which don´t understand the new algorithm. Default is
107           no.
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109           This variable is superseded by the ENCRYPT_METHOD variable or by
110           any command line option used to configure the encryption algorithm.
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112           This variable is deprecated. You should use ENCRYPT_METHOD.
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114       SHA_CRYPT_MIN_ROUNDS (number), SHA_CRYPT_MAX_ROUNDS (number)
115           When ENCRYPT_METHOD is set to SHA256 or SHA512, this defines the
116           number of SHA rounds used by the encryption algorithm by default
117           (when the number of rounds is not specified on the 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 to
121           authenticate users.
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123           If not specified, the libc will choose the default number of rounds
124           (5000).
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126           The values must be inside the 1000-999,999,999 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 value
132           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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