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This article summarizes common commands for linux user and group management. Share with you for your reference, the details are as follows:

1. The user belongs to the user group.

2. User and user group profile

1) user Group Profil

/ etc/group

First column: group name of the user group

Second column: group password (the real password is stored in gshadow)

The third column: user group ID, unique identity of user group

The superuser group with group ID of 0

Group ID is 1-499 is the system user group

Group ID greater than 500is a user-defined group

Fourth column: group members

2) user group password profile

/ etc/gshadow

First column: user group name

Second column: password

The third column: group administrator

Fourth column: group members

3) user profile

/ etc/passwd

First column: user name

Second column: user password, with only one x placeholder, password stored in shadow

The third column: user ID, unique ID

The user whose ID is 0 is the superuser.

Users whose ID is 1-499 are system users.

A user whose ID is greater than 500is a custom user

Fourth column: group ID of the group to which it belongs

Column 5: remarks

The sixth column: the user's home directory (home). When the user logs in to the system, he or she logs in at home.

The seventh column: shell type

4) user password profile

/ etc/shadow

First column: user name

The second column: password (! Indicates that there is no password and login is not allowed.

3. User group management

Groupadd group name add user group

-g: specify the group ID when adding a group

Groupmod group name modifies user group information

-n: modify the group name

-g: modify the group ID

Groupdel group name delete group

* if there are users under a group, the group cannot be deleted.

4. User management

Useradd [parameter] username add user

-g group name specifies the group to which it belongs

-d directory specifies the user home directory

* when adding a user, if you do not specify a group, the system creates a group with the same name as the user.

Usermod [parameter] user name

-c comment modify remarks information

-l user name modify user name

-d directory modify user home directory

-g group name modify user group

Userdel [parameter] user name

-r Delete user home directory

5. Password management

Passwd [option] user name

-S to view the password status of the user

-l lock the user's password (no login is allowed)

-u unlock the user's password

-d delete user password

6. Forbid account login

There are two situations:

Forbid a certain account to log in

/ etc/shadow

Modify shadow directly and add two before the user's password! The user is not allowed to log in.

It is recommended to use: passwd-l user name this method to prevent users from logging in.

All accounts are prohibited from logging in

/ etc/nologin

Create a nologin file under / etc/, and no user can log in.

7. Add and delete group members

* usermod-g is the primary group of the modified user

Gpasswd [options] group name

-a user name: add group members

-d user name: delete group member

The default identity of a user after logging in is his primary group identity.

You can use newgrp to switch the identity of the group to which it belongs, as long as it also belongs to that group.

The group to which the current user identity is switched is the group to which the created file belongs.

I hope what is described in this article will be helpful to everyone's Linux management.

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