gpasswd - administer /etc/group and /etc/gshadow
|gpasswd [选项] 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.
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.
-Q, --root CHROOT_DIR
Apply changes in the CHROOT_DIR directory and use the configuration files from the CHROOT_DIR directory.
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.
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,...
-M, --members user,...
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:
It can take one of these values: DES (default), MD5, SHA256, SHA512.
Note: this parameter overrides the MD5_CRYPT_ENAB variable.
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).
此功能(分割组)允许限制组文件中的行长度。这对于确保 NIS 组的行比长于 1024 字符。
注意：分割组可能不受所有工具的支持(甚至在 Shadow 工具集中)。您不应该使用这个变量，除非真的需要。
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 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.
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).
使用很多轮转，会让暴力破解更加困难。但是需要注意，认证用户时也会需要更多的 CPU 资源。
值必须在 1000 - 999,999,999 之间。
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.