CentOS methods for adding and removing users and user groups

1. Account Linux environment mainly in/etc passwd system files, / etc/shadow, / etc/group, and etc/gshadow4 files. 1. The uid of root is 0, starting from 1-499 is the standard account of the system, and ordinary users start from uid 500.

usermod  options   The user name // Modify existing users 
userdel -r  The user name // Deleting a user represents their home directory 1 To delete. 
groupadd  options   Group name //  Add a new set of 
groupmod  options   Group name // Modify an existing group 
groupdel  Group name  // Delete specific groups that already exist. 

Example 2.

Add and remove user commands under CentOS:

Add user test:

adduser test

Change test password:

passwd test

Delete User test:

userdel test

Delete users and user directories:

userdel -r test

Create a new sudo user group

groupadd sudo

Create a new user, test, and join the suso additional group

useradd -G sudo test

Create 1 new user ftpadmin, specify directory as /var/ftp/pub, do not create your own directory (-ES52en)

useradd -d /var/ftp/pub -M ftpadmin

Means to add zh888 to the additional group sudo, which is a new existing user

usermod -G sudo zh888

Means remove directory 1 from zh888 and /home.

userdel -r zhh888

To delete the sudo group

adduser test

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After the user is created, add a password to the user, and set the imperative passwd passwd option user name

User name Account name // User account password is prohibited

adduser test

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User name // represents the view of user account password status

adduser test

2

User name // means restore user account

passwd -u

The user name // represents the deletion of the user account password

adduser test

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4. The chage command is timed to protect the password so that it prevents others from guessing the password.

chage option user name

Parameters have

-m days -M days -d days -I days -E date -W days -l

Example:

The user zhh is required not to change the password within two days, and the maximum password survival is 30 days, and the user is required to notify zhh five days after the password expires

adduser test

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5. User and group status query commands

Displays the current user name.

whoami

Indicates the group to which the specified user belongs or, if no user is specified, the group to which the current user belongs

groups user name

Switch to another user, if su means switch to your current user.

adduser test

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Converts the user's current group to the specified additional group, to which the user must belong

adduser test

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6. Change owner and group

Sometimes you also need to change the owner and the group to which the file belongs. Only the owner of the file has the right to change other owners and groups. Users can transfer their own files to others. Change file ownership using the chown command

chown [-R] <  User name or group ><  File or directory >

example

Change file files owner to www user

adduser test

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Change the owner and group of file files to www

chown www.www file

Change the home and group of all files or directories in files to www in all directories and subdirectories

chown -R www.www files/

7. Set the directory of the file and the directory generation mask

Users can use the umask command to set the default build mask for the file. The default build mask tells the system what permissions should not be granted to create a file or directory. If users place the umask command in the environment file.bash_ES174en, they can control access to all newly created files and directories.

umask [a1a2a3] a1 means permission not allowed to belong to a master, a2 means permission not allowed to belong to a group, and a3 means permission not allowed to belong to others.

umask 022// Indicates that the Settings do not allow group users and other users to have write permissions. 
umask // Displays the current default build mask. 

8. Setting of special permissions

passwd test

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In addition to general permissions, there are special permissions, 1 some special permissions exist special permissions, if the user does not need special permissions 1 do not open special permissions, to avoid security problems