Linux user groups and Rights management

in the Linux each user in must belong to a group and cannot be independent of the group. Each file in Linux has the concept of owner, group, other group

In a Linux system, the user account that is created and its associated information (except for passwords) are stored in the/etc/passwd configuration file. Because all users have read permissions to the passwd file, the password information is not stored in the file, but is saved in the/etc/shadow configuration file.

1, in the passwd configuration file, the corresponding relationship of the fields from left to right and their meanings:

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2, user password management

In the shadow configuration file, the corresponding relationship of the fields from left to right and their meanings:

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3. Group Information Management files

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User Management commands:

Add user command: Useradd

Modify user command: passwd

Modify User rights: Usermod

Delete User: Userdel

Switch User: Su

A template file home directory is generated when a user is added

/etc/skel

When a user is created, the files are automatically copied in their home directory (based on the template (Files under the template directory))

usermod [Options] User name

-U uid modifies the UID number of the user

-C User Description Modify User's description information

-G Group name Modify User's additional group

-G initial Group modified initial Group

- L temporary lock User (lock)

- u unlock user lock (Unlock)

Example: Adding Harry to the admin group

[[email protected] app] #usermod-G admin Harry

[[email protected] app] #id Harry

uid=1002 (Harry) gid=1003 (Harry) groups=1003 (Harry), 1006 (admin)

3. modifying user information Usermod
Modify user password status chage
usermod [options] User name
-u UID Modified user uid number
-c User Description Modify User's description information
-g Group name Modify user's additional group
-g Initial group Modify initial group
-l temporary lock User (lock)
-u Unlock user lock (Unlock)

Modify User Password status
chage [Options] User name
-l lists the user's detailed password status
-D Date Change Password last modified date (third field of shadow)
-m number of days two password modification interval (Shadow fourth field)
-m number of days password expiration (5th field)
-W Number of days before password expiration warning (6th field)
-I days Grace days after password expires (7th field)
-e Date Password Expiration time (8th field)

User Group Management
1. Add a user group
Groupadd [Options] Group name
-G GID: Specify Group ID
2. Modify user groups
Groupmod [Options] Group name
-G GID: Modify Group ID
-N New group name: Modify Group name
Groupmod-n Newgroup_name Group_name
Change the group name Group_name to Newgroup_name
3. Delete a group name
Groupdel Group Name
This group cannot be deleted when the group is the initial group of a user and the user exists
You have to delete the initial user first.
Groups with additional users who do not have an initial user can delete
Groupadd Gr1
Useradd-g Gr1 U1
Useradd-g Gr1 U2
Does not produce U1 group, U1 user's initial group is GR1.

4. Add users to or remove from a group
GPASSWD [Options] Group name
-A user name: Add user to Group (add-on user)
-D Username: Remove the user from the group

Linux user groups and Rights management