What are the regulations for user groups in Linux systems?

1User management 1.1useradd add user

Basic sentence pattern: useradd username (function description: add new user)

Case: [root@lagou~]#useraddhadoop

1.2passwd sets user password

Basic sentence pattern: passwd username (function description: set user password)

Case:

1.3id determines whether the user exists

Basic sentence pattern: id username

Case:

1.4su switch user

Basic sentence pattern:

Case:

[root@lagou~]#suhadoop

[root@lagou~]#su-hadoop

1.5userdel delete user

Basic sentence pattern:

userdel username (function description: delete the user but save it in the owner's directory)

userdel-r username (function description: delete the user and user directories)

Case:

1.6who View logged in user information

Basic sentence pattern:

1.7 Set Linux ordinary users to have root permissions, that is, the use of sudo

sudo command:

sudo is a linux system management command. It is a tool that allows system administrators to let ordinary users execute some or all root commands. linux sets user group permissions, such as halt embedded linux training, reboot, su and so on. In addition to reducing the login and management time of the root userlinux setting user group permissions, this also enhances security.

Change configuration file:

Change the /etc/sudoers file, find the line below, and add a line under root, as shown below: vim/etc/sudoers

Log in as user tom and operate the administrator command

Essence: Use temporary administrator rights

1.8 Check what users have been created

Basic sentence pattern: cat/etc/passwd

2User Group Management

Introduction: Each user has a user group, and the system can centrally manage all users in a user group. Different Linux systems have different regulations on user groups. For example, a user under Linux belongs to a user group with the same name. This user group is created at the same time when the user is created. The management of user groups involves adding, deleting, and changing user groups. Lowering, deleting and changing groups are actually updates to the /etc/group file

2.1groupadd new group

Basic sentence pattern: groupadd group name

Case:

Lower a hadoop group: groupaddhadoop

2.2groupdel delete group

Basic sentence pattern: groupdel group name

Case:

Delete hadoop group: groupdelhadoop

2.3groupmod changes group

Basic sentence pattern: groupmod-n new group name old group name

Case:

Change the hadoop group name to hadoop1:groupmod-nhadoop1hadoop

2.4 Check what groups were created

Basic sentence pattern: cat/etc/group

2.5usermod changes the group to which the user belongs

Basic sentence pattern: usermod-g user group username

Case:

Add user hadoop to mygroup user group: sermod-gmygrouphadoop

3File Permissions

Introduction: The Linux system is a typical multi-user system. Different users are in different positions and have different permissions. In order to protect the security of the system, the Linux system has different regulations on the permissions of different users to access the same file (including directory files). In Linux, we can use the ll or ls-l command to display the attributes of a file and the user and group to which the file belongs.

3.1 File Permissions

Explanation based on letter position:

Permissions are segmented, each segment represents a different user:

3.2 File permission management

Change file permissions:

3.3chown changes owner

Basic sentence pattern: chown end user (function description: change the owner of a file or directory)

Case: [root@lagoutest]#chownhadooptest1.txt

3.4chgrp changes the group it belongs to

Basic sentence pattern: chgrp end user group (function description: change the group to which a file or directory belongs)

Case:

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