VI text editor and user rights management, group management and time management

vi Text editor

     1. install ：yum -y  install   vim*
     2.  vi/vim Three modes of and the conversion between each mode 

3. Edit commands and shortcuts

          Insert command :( General mode goes into insert mode )：
         i	 Insert... In front of the cursor 
         I	 Insert... At the current line of the cursor 
         a	 Insert... After the cursor 
         A	 Insert... At the end of the current line of the cursor 
         o	 Insert a new line next to the current line of the cursor 
         O	 Insert a new line on the previous line of the cursor's current line 

          Locate the command （ Write in bottom line mode ）：
         :set nu	 According to the line Numbers   
         :set nonu	 Cancel the line Numbers 
         :n	 To... Of the text n That's ok 
         gg	 Go to the first line of the text G	 To the last line of the text   


          Replace and cancel commands （ In general mode ）:  
         u	undo, Cancel the previous operation  ctrl + r 	redo, Back to undo Before  
         r	 Replace character at cursor 
         R	 Replace from where the cursor is , Press Esc Key end 

          The delete command :
         x	 Deletes the character where the cursor is 
         nx	 Delete... After the cursor n Characters 
         dd	 Deletes the line where the cursor is located .
         ndd   Delete n That's ok 
         dG	 Delete all contents from the cursor line to the end line 
         D 	 Delete the content from the cursor to the end of the line 
         :5,7d	 Deletes the row of the specified range 

          Common shortcut key :
         Shift+ zz 		 Save and exit , And “:wq” The same effect 
         v			 Enter character visual mode 
         V   or   Shift + v	 Enter line view mode 
         Ctrl + v		 Enter block view mode 
         ctrl+b: Screen moves back one page 
         ctrl+f: Move the screen forward one page 
          Press "$" Symbol moves the cursor to the end of the line 
          Press "^" Move the cursor to the beginning of the line 
         yy： Copy cursor line to buffer .
         nyy： for example ,「6yy」 Indicates that the copy is from the line where the cursor is located " Count down "6 Line text .     
         Linuxroot password ：aaaqy142

4. User authority management , Group management and time management

1. A file that holds user information ：/etc/passwd
2. A file that stores user password information ：/etc/shadow
3. The user classification ：
The super user ：（root,UID=0）
Ordinary users ：（UID stay 1000 To 60000）
Dummy user ：（ UID stay 1 To 999）
4. Add user command useradd
-u Designated user ID（uid）
-g Specify the group name to which you belong （gid） The main group
-G Specify multiple groups , Comma “,” Separate （Groups） Other groups
-c User description （comment） ;
-e Failure time （expire date）
establish ：
useradd -u 1888 -g users -G sys,root -c " Description information "uqy142a
（centos 7 Previous version , Pseudo user from 1-999 centos7 Then the pseudo user uses 1-999 Ordinary users of the current version ID Should be 1000 To 60000）
Set the password ： passwd uqy142a// Set the password twice
Switching users su su -l uqy142a
5. Modify user command ：usermod（user modify）
l Change user name （login）usermod -l a b（b Change it to a）
usermod -l uqy142cc uqy142c
-g add group usermod -g sys tom
usermod -g root uqy142a
-G Add multiple groups usermod -G sys,root tom
usermod -G sys,users uqy142a
–L Lock user account password （Lock） usermod -L uqy142b // lock b user , Even if ordinary users are locked ,root You can still log in
–U Unlock user account （Unlock）
su -l root // Switch to root Unlock
usermod -U uqy142b su -l uqy142a
su -l uqy142b // The password is found to be correct , Switch users

6. Delete user command ：userdel
userdel uqy142d // Just delete user information
userdel -r uqy142e When deleting an account, delete the directory （remove

5. Group management

 Save user group files ：/etc/group
 add group ：groupadd：
groupadd -g  16666  groupa        -g  Appoint gid
tail  /etc/group  // After displaying the file 10 That's ok    
 Modify the set of ：groupmod
groupmod  -n  groupaa  groupa  // hold groupa Change the name of groupaa
groups  Display the user's group 
groups   uqy142a
 Other group related commands ：
 chgrp   Change the group to which the directory or file belongs （ Reorganize only ）
  ll |grep aaa   // see aaa Subordinate to the group 
  chgrp groupb  aaa     change aaa Original group root  Change it to groupb
 chown  	  Change directories or files   Users and groups 
 ll |grep aaa     // see aaa Users and groups 
 chown uqy142a:groupc aaa      // change aaa The user and group of the directory         
 chown -R  uqy142a:groupc aaa   //  The catalogue of descendants has changed  

6.Sudo command

 It is generally used in the non-medical field root Under the user , Temporary promotion is not root User's rights .
 First step ： Must be in /etc/sudoers Non root user 
 The second step ： Carry out orders sudo reboot, Input user1  Password , Restart successful .
su -l   uqy142a           
sudo  shutdown -h now    // Tips uqy142a be not in sudoers In file     Have no authority to execute 
su -l root
vim /etc/sudoers
:100
 Copy 100   Change user name 
su -l uqy142a
sudo  reboot   //  It's restarted 
 Any other ordinary user cannot execute commands , You can do that ....                  

7. time management

 Synchronization time 
yum -y install  ntp  ntpdate           install ntp  ntpdate service 
ntpdate cn.pool.ntp.org      Manual sync ：