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How to understand the file permissions and user identity under Linux, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain in detail for you, people with this need can come to learn, I hope you can get something.

Everything is a file in Linux, so read, write and execute files in Linux, how to add, modify and delete user information in Linux system, and how to use SUID,SGID,SBIT to set system permissions.

Linux is a multi-user, multi-task operating system with good stability and security. One of the original intentions of the design of Linux is to meet the needs of multiple users working at the same time, so user security is very important.

Useradd

You can use useradd to create a user account. When you create a user account using this command, the default user home directory is in / home, the default shell command is / bin/bash, and a basic user group with the same name as the user is created by default

Groupadd

Users create user groups, and in order to efficiently assign permissions to users in the system, they often put multiple users into one group in their work, so as to uniformly arrange permissions and other operations.

Usermod

To modify the user's attributes, everything in Linux is a file, so modifying the user's attributes is essentially the process of modifying the configuration file.

Passwd

Used to change password, expiration time, authentication information, ordinary users can only change their own password

Userdel

To delete a user, when we confirm that a user will no longer log in, we need to delete all messages for this offer. When we delete, the home directory will be retained by default, and you can use-r to delete it at the same time.

Special permissions for files

In the complex and changeable production environment, simply setting the rwx permissions of files can not meet our needs for security and flexibility, so we have the special permission bit of SUID,SGID,SBIT, which is a special function of setting file permissions.

SUID

Is a special permission to set the binary program, which allows the executor of the binary program to have the authority of the owner temporarily.

SGID

There are two main functions: first, let the executor have the permission to belong to the group temporarily. Second, files created in a directory automatically inherit the user groups of that directory

SBIT

The server can set specific directories, so in order to protect the files inside from being maliciously deleted, you need SBIT. When SBTI is set, only the executor can delete it.

Charrt

Used to set hidden permissions for files

Lsattr

Hidden permissions used to show files

Setfacl

ACL rules used to manage files. The so-called ACL rules actually control the read and write permissions of a single user or user group other than the read and write permissions of the owner, the group to which they belong, and others.

Getfacl

Used to display ACL information set on the file

Su

Switch user identity

Sudo

Give ordinary users extra permissions to perform things that root administrators should be able to do

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