One 、 user and jurisdiction Basic concepts of

1、 user

• user Is in Linux An important part of the system work , User management Include user And Group Management of

• stay Linux In the system , Whether by the local machine or the remote login system , Every system You have to have an account , And for the Different system resources have different permissions

• stay Linux in , You can specify Every user in the light of Different files or directories Of Different authorities

• Yes file / Catalog The authority of includes ：

  jurisdiction	english	narrow	Number code
  read	read	r	4
  Write	write	w	2
  perform	excute	x	1
  No authority		-	0

2、 Group

• To facilitate user management , Put forward Group The concept of
• in application , In advance in the light of Group Set permissions , And then Different users are added to the group for , So you don't have to set permissions for each user in turn

3、ls -l Detailed description of display information

• ls -l You can see Details of the files under the folder , From left to right ：

  • jurisdiction , If the first character is d Presentation directory , If it is - Said file
  • Hard link number , Generally speaking , Is how many ways you can access At present Catalog / file
  • The owner , Files in the home directory / Catalog The owner of is usually the current user
  • Group , stay Linux Kind of , A lot of times When the group name and user name are the same
  • size
  • Creation or last modification time
  • name

• A detailed introduction to the number of hard links :

  Be careful : The number of hard chain connections of files is generally 1, The more subdirectories of a directory , The more hard links it has
  

Two 、 User permissions —chmod Simple use of commands

• chmod You can modify user / Group Yes file / Catalog Authority

• The command format is ：chmod +/-rwx file name / Directory name

  Be careful ： If it is + , said Increase the permissions ; if - Number , It means to reduce permissions

  ​ rwx The three permissions can be combined at will

3、 ... and 、 The super user

• Linux In the system Of root account number Usually For system maintenance and management , All resources of the operating system With all access rights
• In most versions of Liunx in , None of them recommend Use it directly root Account login system
• stay Linux During installation , The system will automatically create a user account , The default user is called “ Standard users ”

sudo

• su yes substitute user Abbreviation , Express Use the identity of another user
• sudo A command is used to execute a command in another capacity , The preset identity is root
• The user to use sudo when , You must enter a password , After a 5 Minutes of validity , If the time limit is exceeded, you must re-enter the password
• If its unauthorized user attempts to use **sudo **, A warning email will be sent to the administrator

Ubuntu Into root Pattern ：

Use sudo su command , To exit root Mode can be used exit perhaps su user( User name when installing ) command

Four 、 Group management Terminal command

• Be careful ：

  • Create group / Delete the group All terminal commands need to be passed sudo Command execution （ Because standard users do not have this permission ）
  • Group information is saved in /etc/group In file
  • /etc Directory is specially used to save System configuration information The catalog of
  • in application , In advance in the light of Set permissions for the Group , Then add different users to the corresponding group , So you don't have to set permissions for each user in turn

  #  add to  dev  Group 
  $ sudo groupadd dev
  
  #  Check whether the group is added successfully 
  $ cat /etc/group
  
  #  take  Python The group of the learning directory is changed to  dev
  $ sudo chgrp -R dev Python Study /
  
  #  Delete  dev Group 
  # sudo groupdel dev
  

5、 ... and 、 User management - Create delete user terminal command

Be careful ：

• Create user / Delete user / Change other user passwords All terminal commands need to use sudo perform

• When you create a user , If you forget to add -m Option to specify the new user's home directory , The simplest solution is Delete user , Recreate

• When you create a user , A and... Are created by default Group name with the same user name

• User information is stored in /etc/passwd In file
  

6、 ... and 、 User management — View user information terminal commands

1.passwd file

/etc/passwd Files store user information , from 6 It's a semicolon 7 Messages , Namely

• user name
• password （x, Means encrypted password ）
• UID（ User ID ）
• GID（ Group ID ）
• User's full name or local account number
• Home directory
• Login using Shell, After login , Terminal commands used ,Ubuntu The default is dash

2.usermod

• usermod Can be used to set user Of The main group / Additional group and Sign in Shell,

• The main group ： You usually specify when you create a new user , stay etc/passwd Of the 4 Column GID The corresponding group

• Additional group ： stay etc/passwd The last column in represents the list of users for this group , Is used to specify the Additional permissions of the user

• Be careful ：

  • After setting the user's additional group , need Login again to take effect

  • By default useradd The added user does not have permission to use sudo With root The identity of the person executing the command , have access to usermod -G sudo user name command , Add users to sudo In additional groups

#  Modify the user's primary group (passwd  Medium  GID)
$ usermod -g  Group   user name 

#  Modify the user's additional groups 
$ usermod -G  Group   user name 

#  Modify user login  Shell
$ usermod -s /bin/bash

3.which

• which Command to see where the command is executed
• Be careful ：
  • /etc/passwd File used to save user information , Unenforceable
  • /usr/bin/passwd Is a program for changing user passwords
  • cd This terminal command is built into the system kernel , There are no separate files , So with which Unable to find cd Command location
• bin and sbin
  • stay Linux in , Most executable files are saved in /bin 、/sbin、/usr/bin 、/usr/sbin
  • /bin(binary) Is the binary executable Directory , It is mainly used for specific applications
  • /sbin(system binary) It is a binary code storage directory for system administrators , It is mainly used for system management
  • /usr/bin(user command for applications) Some software installed later
  • /usr/sbin(super user commands for applications) Some hypervisors for super users

4. Switching users

• su No user name , You can switch to root , But not recommended , unsafe
• If it is in the current directory Input exit , will sign out Shell A terminal window

5. Modify file permissions

The command format is as follows ：

#  Modify file / The owner of the catalog 
$ chown  user name   file name / Catalog 

#  Recursively modify files  /  Group of directories 
$ chgrp -R  Group name   file name / Catalog 

#  Recursively modify file permissions 
$ chmod -R 755  file name / Catalog 

• Be careful ：
  • chmod When setting permissions , You can simply use three numbers to correspond to each other The owner / Group And others User's rights
  • Use it directly chomd +/- rwx file name / Directory name You can modify file / Catalog Of read | Write | perform jurisdiction , But it can't be accurate to The owner | Group | other