This article will further learn the linux commands that must be mastered, and master these commands to make the computer understand you better.
As far as the centos operating system we have installed above is concerned, we usually operate in two ways: the first is to operate graphically through the desktop; the other is to enter commands through the terminal.
For the server, we usually use a remote connection tool to connect to the server, and then manage it by command. How does a computer know what to do when we type a command? Then you have to rely on command line tools (also called terminals) to translate and interpret, and then call the corresponding interface services to complete specific functions.
The interaction between the user and the linux system is through the shell terminal. The following section will first analyze the shell command line tools, and then explain the most basic linux commands.
1. Introduction to shell
Computer hardware is composed of arithmetic unit, controller, memory, input/output devices, etc., and the thing that allows various hardware devices to perform their own functions and work together is the system kernel. The kernel of the Linux system is responsible for completing management tasks such as allocation and scheduling of hardware resources. Therefore, the system kernel is very important to the normal operation of the computer. Generally, it is not recommended to edit the parameters in the kernel directly, but to allow users to manage the computer through programs or services developed based on the system call interface to meet the needs of daily work. The shell is such a client-side command-line tool that acts as a bridge between the user and the system kernel.
Shell, also known as "terminal" and "shell", is a command-line tool written in C language, acting as a translator between humans and the kernel (hardware). The user "tells" some commands to the terminal, and it will call the corresponding command. The program service to do some work.
1.1 shell version
Listed below are several shell versions
- sh (Bourne Shell): It is the shell originally used by UNIX and can be used on every UNIX. Great at shell programming, but not as good at handling interaction with the user as several other shells.
- bash (Bourne Again Shell): Linux default, is an extension of Bourne Shell. It is fully compatible with Bourne Shell, and adds many features such as command completion, command history, etc. It also contains many advantages of C Shell and Korn Shell, has flexible and powerful editing interface, and has a very friendly user interface.
- csh (C Shell): A more suitable variant of the Bourne Shell, the syntax is very similar to the C language.
- Tcsh: An extended version of the C Shell provided by Linux. Including command line editing, programmable word completion, spell correction, historical command substitution, job control and C-like syntax, it is not only compatible with the Bash Shell prompt, but also provides more prompt parameters than the Bash Shell.
- ksh (Korn Shell): It combines the advantages of C Shell and Bourne Shell and is fully compatible with Bourne Shell.
- pdksh: An extension to ksh provided by Linux systems. Support character control, you can suspend on the command line, execute in the background, wake up or terminate the program.
The default terminal used by many mainstream Linux systems, including Red Hat, is the Bash (Bourne-Again SHell) interpreter. The mainstream Linux system chooses the Bash interpreter as the command line terminal mainly because of the following four advantages:
The installed centos7 also uses the bash terminal by default. When using a remote connection tool to connect to centos7, the default open terminal is bash, which can be viewed by entering the command in the terminal: echo $SHELL, and the result is: /bin/ bash.
- How to judge the type of the current terminal?
via "echo $SHELL" command or via "evn" terminal command
- How do I change the terminal type I log in to?
Use the terminal command chsh, such as: chsh -s /bin/bash to change the login terminal to bash
1.2 Shell Command Types
A shell is a program that is used by the user to interact with the operating system, and is equivalent to a command parser.
As an interface between the user and the kernel, it is both a command language and a programming language. Shell commands are further divided into built-in commands and external commands.
- built-in commands
The internal command is actually a part of the shell program, which contains some relatively simple linux system commands. These commands are recognized by the shell program and run inside the shell program. Usually , the shell is loaded and resident when the linux system loads and runs. in system memory . Internal commands are written in the bashy source code, and their execution speed is faster than external commands, because parsing the internal command shell does not require the creation of subprocesses. For example: exit, history, cd, echo, etc.
- external command
The external command is the utility part of the linux system. Because the function of the utility program is usually relatively powerful, the amount of programs it contains will also be large . only when it is called into memory . Usually the entity of the external command is not contained in the shell, but its command execution process is controlled by the shell program . The shell program manages the path search, loading and storage of external command execution, and controls the execution of commands. External commands are installed outside of bash, usually in /bin, /usr/bin, /sbin, /usr/sbin...etc. You can view the storage path of external commands through the "echo $PATH" command, such as: ls, vi, etc.
How to distinguish whether it is an internal command or an external command?
- Through the type command, such as: type cd can see that it is an internal command; type mkdir can see that it is an external command.
- Through the man command, such as: man cd, it will prompt that it is a built-in command of bash; man ls, it will prompt that it is an external command.
The biggest difference between internal commands and external commands is performance. Internal commands execute much faster than external commands because they are built into the shell and do not have to create extra processes. So just like executing a larger script, executing a script that contains many external commands can hurt the performance of the script.
The most commonly used commands
Now that there is already a "translator" such as Bash in the Linux system, it is necessary to learn how to communicate with it. In order to complete various tasks accurately and efficiently, it is not enough to rely only on the command itself, and the parameters of various commands should be flexibly adjusted according to the actual situation.
The general format of linux execution command: command name [command parameter] [command object]
Separate command names, command parameters, and command objects with a space bar. Command objects generally refer to files, directories, users and other resources to be processed, and command parameters can be in long format (--) or short format (-).
Long form: man --help
Short form: man -h
There are many linux commands, and the most important thing is the combination of various parameters. It is impossible for a novice to remember all the parameters, and it is necessary to check them frequently through the help command.
Special note: In the terminal, sometimes a lot of content is displayed, and you can browse through the shortcut keys.
shift PgUp: page up
shift PgDn: page down
2.1 Help commands
There are two main help commands: man and help. Usually, there are more help commands. If you encounter an unclear command, use the help command to check it. You don't need to memorize it by rote, and practice makes perfect.
2.1.1 man command
Syntax: man [command or configuration file]
Function: Get help information
Case:
[root@heimatengyun ~]# man date
For example, if you want to view the usage of the date command, after entering the command man date, the following information will appear
Since there is a lot of help information, you need to turn the page to read it, so first explain that this interface may need to use the keys and their purposes.
|
button |
use |
|
space bar |
page down |
|
PgDn （page down） |
page down |
|
PgUp （page up） |
page up |
|
home |
Go to homepage |
|
end |
go to footer |
|
/ |
Search keywords from top to bottom, such as "/linux" |
|
? |
Search keywords from the bottom up, such as "?linux" |
|
n |
Locate the next searched keyword |
|
N |
Locate the last searched keyword |
|
q |
Exit the help file |
When a beginner looks at it, so much help information is confusing. In fact, it is very simple. Let's take a look at the structure of the help information (the part circled with the red line in the above figure).
|
structure name |
illustrate |
|
NAME |
the name of the command |
|
SYNOPSIS |
Basic syntax of commands |
|
DESCRIPTION |
Explain in detail the usage of options and parameters corresponding to the syntax format |
|
EXAMPLES |
Example of how to use the command |
|
OVERVIEW |
Overview |
|
DEFAULTS |
Default function |
|
OPTIONS |
specific options available |
|
ENVIRONMENT |
environment variable |
|
SEE ALSO |
Relevant information, usually man pages |
Through these help information, you can easily grasp the usage of each command.
2.1.2 help command
Syntax: help command
Role: Get help information for shell built-in commands
Case:
[root@heimatengyun ~]# help cd
Before officially entering the command learning, let 's introduce a few common shortcut keys in linux
|
hot key |
effect |
|
ctrl l |
clear screen |
|
ctrl q |
quit |
|
ctrl c |
stop process |
|
Up and down keys |
Find commands executed in the past |
|
tab |
Command completion, multi-purpose not only improves efficiency but also prevents typing mistakes |
Since everything in linux is a file, after understanding the omnipotent help command, we will start learning from the directory file command.
2.2 Directory related commands
The directory can classify and manage files, so the directory-related commands are explained before the file commands are explained.
2.2.1 pwd
Syntax: pwd
Function description: Display the absolute path of the current working directory
Case:
[root@heimatengyun ~]# pwd
/root
2.2.2 ls
Syntax: ls [options] [directory or file]
Function description: List the files in the directory
Options:
-a(--all): show all files, including hidden files (files starting with .)
-d：directory，列出目录本身
-l: long long data string list, including file attributes and permissions, etc. The information listed on each line is: file type and permissions, number of links, file attributes, file group, file size (byte), creation or last modification time, name
Case:
[root@heimatengyun test]# ls -al
total 12
drwxr-xr-x. 2 root root 37 Nov 24 10:43
.dr-xr-x---. 16 root root 4096 Nov 24 00:02
..-rw-r--r--. 1 root root 26 Nov 23 20:40
test1.txt-rw-r--r--. 1 root root 66 Nov 23 21:56 test.txt
2.2.3 cd
grammar:cd [option][dir name]
Function description: switch to the specified directory
Case:
cd absolute path or relative path (jump to the specified directory)
cd or cd ~ (returns the current user home directory)
cd - (return to the last directory)
cd .. (return to the previous directory of the current directory)
2.2.4 mkdir
Syntax: mkdir [options] directory name
Function description: Create the specified directory
Options:
-p : parents, create multi-level directories
Case:
[root@heimatengyun ~]# mkdir test
[root@heimatengyun ~]# mkdir -p test1/test1
2.2.5 is rm
Syntax: rmdir [options] directory name
Function description: delete empty directory
Options:
-p: delete multi-level directories
Case:
[root@heimatengyun ~]# rmdir test
[root@heimatengyun ~]# rmdir -p test1/test1/ (If the -p parameter is not specified, only the directory whose last level is not empty will be deleted)
2.2.6 cp
Syntax: cp source directory or file target directory or file
Function description: copy directory or file
Options:
-r: recursive, recursively copy the entire folder
Case:
Copy test as test.txt, rename it when copying
[root@heimatengyun ~]# cp test test.txt
Copy all test directory contents to test1 directory (automatically create test1 directory)
[root@heimatengyun ~]# cp -r test test1
2.2.7 mv
Syntax: mv [options] source target
Function description: move files or rename files
Case:
Rename the test file to test.txt
[root@heimatengyun test]# mv test test.txt
Move the test directory and all its contents to the test2 directory, and automatically create the test2 directory (it can be understood as renaming the test folder to test2)
[root@heimatengyun ~]# mv test/ test2
2.2.8 rm
Syntax: rm [options] file
Function description: delete files and directories
Options:
-f: force to enforce
-r: recursive recursive execution
Case:
Recursively delete a directory and everything under it
[root@heimatengyun ~]# rm -rf test2/
2.3 File related commands
Everything in linux is a file. After connecting the directory-related commands, this section learns the file-related commands.
2.3.1 touch
Syntax: touch [options] filename
Function description: Create empty file
Case:
[root@heimatengyun test]# touch test.txt
echo
Syntax: echo string or variable
Function description: output string or variable value, and can also store content to file with slave directional character
Case:
[root@heimatengyun test]# echo hello
hello
[root@heimatengyun test]# echo $SHELL
/bin/bash
[root@heimatengyun test]# echo linux >> test.txt
2.3.2 cat
Syntax: cat [options] filename
Function description: View the content of the file, starting from the first line
Options:
-A: List special characters instead of whitespace
-b: List line numbers, blank lines are not counted as line numbers
-n: List line numbers, blank lines will also have line numbers
-v: List some invisible special characters
Case:
[root@heimatengyun test]# cat test.txt
hello
who are you
where are you from
[root@heimatengyun test]# cat -A test.txt
hello$
who are you$
$
where are you from$
[root@heimatengyun test]# cat -b test.txt
1 hello
2 who are you
3 where are you from
[root@heimatengyun test]# cat -n test.txt
1 hello
2 who are you
3
4 where are you from
2.3.3 more
Syntax: more [options] file
Function description: View file content, display page by page
Instructions for use:
Space bar (space): page down
enter: scroll down a line
q: Exit more, no longer display file content
ctrl f: scroll down one screen
ctrl b: return to the previous screen
=: output the line number of the current line
:f: output file name and current line number
2.3.4 head
Syntax: head [options] file
Function description: View the content of the file, only the first few lines
Options:
-n: view the first n lines
Case:
[root@heimatengyun test]# head -n 2 test.txt
2.3.5 tail
Syntax: tail [options] file
Function description: View the content of the file, only the last few lines of the file
Options:
-n: last few lines
-f: follow the content of output file modifications, used to track file modifications
Case:
[root@heimatengyun test]# tail -n 2 test.txt
2.3.6 wc
Syntax: wc [options] text
Function description: Count the number of lines, words and bytes of the specified text
Options:
-l: lines display the number of lines
-w: display the number of words
-c: display the number of bytes
Case:
[root@heimatengyun test]# cat test.txt
hellowho are youwhere are you form?wellcomehahahtest
[root@heimatengyun test]# wc -l test.txt
8 test.txt[root@heimatengyun test]# wc -c test.txt
60 test.txt[root@heimatengyun test]# wc -w test.txt
11 test.txt
2.3.7 stat
Syntax: stat [options] file
Function description: View the specific storage information and time of the file
Case:
[root@heimatengyun test]# stat test.txt
File: ‘test.txt’
Size: 60 Blocks: 8 IO Block: 4096 regular file
Device: fd01h/64769d Inode: 2160373 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
Context: unconfined_u:object_r:admin_home_t:s0
Access: 2019-11-23 18:27:02.153101936 0800
Modify: 2019-11-23 18:26:56.254259870 0800
Change: 2019-11-23 18:26:56.254259870 0800
Birth: -
2.3.8 cut
Syntax: cut [options] file
Function description: Extract text characters by column
Options:
-d: delimiter separator
-f: fields column to extract
Case:
Query all user names in the system
[root@heimatengyun test]# cut -d: -f1 /etc/passwd
root
bin
daemon
adm
lp
sync
...
2.3.9 diff
Syntax: diff [options] file1, file2
Function description: Compare the differences of multiple texts
Options:
--brief: show whether the compared files are the same
-c: context tag displays different content
2.3.10 dd
Syntax: dd [parameter or option]
Function description: Copy files or convert files according to the specified size or number of databases
parameter:
if: the input file name
of: output file name
count: Set the number of blocks to be copied
bs: bytes file block size
Case:
Create a file with a specified size of 10M
[root@heimatengyun test]# dd if=/dev/zero of=10_file count=1 bs=10M1 0 records in1 0 records out10485760 bytes (10 MB) copied, 0.0102506 s, 1.0 GB/s
[root@heimatengyun test]# ll
total 10248
-rw-r--r--. 1 root root 10485760 Nov 23 21:05 10_file
2.3.11 file
Syntax: file filename
Function description: View file type
Case:
[root@heimatengyun test]# file test.txt test.txt: ASCII text
2.3.12 wget
Syntax: wget [parameter] [url address]
Function: download network files
parameter:
-b: background background download
-P: directory-prefix download to the specified directory
-t: tries maximum number of attempts
-c: continue the breakpoint resume
-p: page-requisites Download all content of the page, including pictures, videos, etc.
-r: recursive recursive download
Case:
Download Baidu logo image
[root@heimatengyun test]# wget https://www.baidu.com/img/bd_logo1.png
--2019-11-23 22:29:45-- https://www.baidu.com/img/bd_logo1.png
Resolving www.baidu.com (www.baidu.com)... 14.215.177.38, 14.215.177.39
Connecting to www.baidu.com (www.baidu.com)|14.215.177.38|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 7877 (7.7K) [image/png]
Saving to: ‘bd_logo1.png’100%[======================>] 7,877 --.-K/s in 0.002s 2019-11-23 22:29:45 (4.43 MB/s) - ‘bd_logo1.png’ saved [7877/7877]
2.4 Find command
Sometimes you need to find the required file from a large number of files or find specific content from a specified file, which requires the use of search-related commands.
2.4.1 find
Syntax: find [search scope] [match condition]
Function description: Find a file or directory
Parameter Description
-name: Find by file name
-user: find by file owner
-size: root find files by file size (n is greater than, -n is less than, n is equal to)
case
Find the test1.txt file in the test directory
[root@heimatengyun ~]# find test/ -name test1.txttest/test1.txt
Find the file in the test directory to find the user root
[root@heimatengyun ~]# find test/ -user roottest/test/test.txt
Find files smaller than 100M in the test directory
[root@heimatengyun ~]# find test/ -size -102400test/test/test.txt
2.4.2 grasp
Syntax: grep [parameters] Find content source files
Function description: Search the file for the line matching the string and output
parameter:
-c:count only output the count of matching lines
-n: line-number Display matching lines and line numbers
Case:
[root@heimatengyun test]# grep -n who test.txt
3:who are you[root@heimatengyun test]# grep -c who test.txt
1
2.4.3 which
Syntax: which [options] command
Function description: Search command directory and alias information
Case:
Search the directory where the cd command is located
[root@heimatengyun test]# which cd
/usr/bin/cd
2.5 Compression and decompression
In order to facilitate transmission or save storage space, sometimes files exist in the form of compressed packages, so it is necessary to understand the commands related to compression and decompression.
2.5.1 takes
Syntax: tar [parameter] package name.tar.gz content to be packaged
Function description: package directory, the compressed file format is .tar.gz
parameter:
-c: create generates a .tar package file
-x: extract unpacks the .tar file
-v: verbose show detailed information
-f: file specifies the compressed file name
-z: pack and compress at the same time
-C: Unzip to the specified directory
Case:
Compress multiple files, compress test.txt and test1.txt into test.tar.gz
[root@heimatengyun test]# tar -zcvf test.tar.gz test.txt test1.txt test.txttest1.txt[root@heimatengyun test]# lltotal 10252-rw-r--r--. 1 root root 26 Nov 23 20:40 test1.txt-rw-r--r--. 1 root root 210 Nov 23 23:57 test.tar.gz-rw-r--r--. 1 root root 66 Nov 23 21:56 test.txt
zip directory
[root@heimatengyun ~]# tar -zcvf test.tar.gz test/
Unzip to current directory
[root@heimatengyun test]# tar -zxvf test.tar.gz
2.5.2 zip and unzip
grammar:
Compression: zip [parameter] package name.zip Content to be compressed
Unzip: uzip package name.zip
Function description: Compress files and directories, common to windows and linux, and can compress directories and retain source files
parameter:
-r: recurse-paths recursively compress directories
Case:
Compress test.txt or test1.txt to test.zip
[root@heimatengyun test]# zip test.zip test.txt test1.txt
adding: test.txt (deflated 15%)
adding: test1.txt (stored 0%)
Unzip test.zip
[root@heimatengyun test]# unzip test.zip Archive: test.zip
inflating: test.txt
extracting: test1.txt
2.5.3 gzip and gunzip
grammar:
Compression: gzip [parameter] file
Unzip: gzip [parameter] file.gz
Function description:
Compression: Compress the file, you can only compress the file into a *.gz file. You can only compress files but not directories, and the original files are not retained after compression and decompression. Compress a single file
Unzip: Unzip the file
Case:
Compressed file
[root@heimatengyun test]# lltotal 8-rw-r--r--. 1 root root 26 Nov 23 20:40 test1.txt-rw-r--r--. 1 root root 66 Nov 23 21:56 test.txt[root@heimatengyun test]# gzip test1.txt [root@heimatengyun test]# lltotal 8-rw-r--r--. 1 root root 54 Nov 23 20:40 test1.txt.gz-rw-r--r--. 1 root root 66 Nov 23 21:56 test.txt
unzip files
[root@heimatengyun test]# lltotal 8-rw-r--r--. 1 root root 54 Nov 23 20:40 test1.txt.gz-rw-r--r--. 1 root root 66 Nov 23 21:56 test.txt[root@heimatengyun test]# gunzip test1.txt.gz [root@heimatengyun test]# lltotal 8-rw-r--r--. 1 root root 26 Nov 23 20:40 test1.txt-rw-r--r--. 1 root root 66 Nov 23 21:56 test.txt
2.6 Date command
Date related commands are used to set or get the system date.
2.6.1 date
Syntax: date [options] [format]
Function description: display or set the time
parameter:
-s: set set the time in string format
Format: (note case sensitivity)
%Y: Display the current year
%m: Display the current month
%d: Displays the current day
%H: Display the current hour
%M: Display the current minute
%S: Display the current number of seconds
%Y%m%d: Display the current year, month and day
" %Y-%m-%d %H:%M:%S": Display the current year, month, day, hour, minute and second (enclosed in quotation marks)
Case:
set time
[root@heimatengyun test]# date -s "2019-11-24 11:05:10"Sun Nov 24 11:05:10 CST 2019
display time
[root@heimatengyun test]# dateSun Nov 24 11:02:21 CST 2019[root@heimatengyun test]# date %Y%m%d
20191124[root@heimatengyun test]# date " %Y-%m-%d %H:%M:%S"
2019-11-24 11:02:55
date to view non-current time (such as the previous day, the next day, take the next week Monday, etc.) and cal to view the calendar command will not be discussed for the time being, and there will be a chance to discuss it later.
2.7 Process thread commands
Tasks exist in the form of processes or threads, so you need to keep an eye on system processes at any time, check whether there are abnormal processes and how each process occupies system resources, and use different process management commands to manage and control processes.
2.7.1 ps
Syntax: ps [options]
Function description: View all processes in the system
parameter:
-a: all displays all programs under the current terminal, including programs of other users (for example, multiple clones of several sessions to execute different commands will also be listed)
-u: userlist Display program status in user-based format
-x: Display all programs, not differentiated by terminals (as mentioned earlier, there are many types of terminals, not only the current terminal)
Case:
[root@heimatengyun test]# ps -aux
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 2966 0.0 0.1 116340 3192 pts/0 Ss Nov22 0:03 -bash
...
Explanation of each item
|
item |
meaning |
|
USER |
which user the process was created by |
|
PID |
Process ID |
|
%CPU |
The percentage of CPU occupied by the process. The higher the occupancy, the more resource-consuming the process. |
|
%MEM |
The percentage of memory occupied by the process. The higher the occupancy, the more resources the process consumes. |
|
VSZ |
The size of virtual memory occupied, in KB |
|
RSS |
The size of the actual physical memory occupied, in KB |
|
TTY |
Indicates which terminal the process is running in, tty1-tty7 represents the local console terminal (tty1-tty6 is the local character interface terminal, tty7 is the graphic terminal), pts/0-255 represents the virtual terminal |
|
STAT |
Process state, common states are: R (running), S (sleep), T (stop state), s (including child processes), (in the background) |
|
START |
Process start time |
|
TIME |
Process execution time, that is, the computing time occupied by the CPU, not the system time |
|
COMMAND |
The name of the command that spawned this process |
2.7.2 top
Syntax: top [options]
Function description: View system health status
parameter:
-d seconds: Delay-time, specify the top command to update every few seconds, the default is 3 seconds.
-i: Idle-process, so that the top command does not show any idle or zombie processes
-p: Monitor-PIDs, only monitor the status of a process by specifying the monitoring process ID
-s: Secure-mode, make top run in safe mode and remove potential dangers caused by interactive commands
Case:
View non-zombie processes, refresh once a second
[root@heimatengyun test]# top -i -d 1
top - 12:39:19 up 1 day, 14:31, 3 users, load average: 0.04, 0.04, 0.05Tasks: 395 total, 1 running, 391 sleeping, 3 stopped, 0 zombie
%Cpu(s): 0.0 us, 1.0 sy, 0.0 ni, 99.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 stKiB Mem: 1870784 total, 720520 used, 1150264 free, 880 buffersKiB Swap: 2097148 total, 0 used, 2097148 free. 238616 cached Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME COMMAND
29987 root 20 0 123936 1868 1160 R 2.0 0.1 0:08.32 top
...
In this interface, you can use the following corresponding keys to sort operations
|
Action keys |
illustrate |
|
shift n |
Sort by PID |
|
shift m |
Sort by memory |
|
shift p |
Sort by cpu usage, default option |
|
q |
exit top |
Interpretation of command results
The first line: task queue information
|
content |
illustrate |
|
12:20:42 |
current system time |
|
up 1 day, 14:12 |
system uptime |
|
3 users |
Number of currently logged in users |
|
load average: 0.08，0.01, 0.05 |
The average load of the system in the previous 1 minute, 5 minutes, and 15 minutes is generally considered to be less than 1, the load is small, if it is greater than 1, the system has exceeded the load |
The second line: process information
|
content |
illustrate |
|
Tasks: 395 total |
The total number of processes in the system |
|
1 running |
Number of running processes |
|
391 sleeping |
sleeping process |
|
3 stopped |
stopping process |
|
0 zombie |
Zombie process, if not 0, you need to manually check the zombie process |
The third line: cpu information
|
content |
illustrate |
|
%Cpu(s): 0.0 us |
CPU percentage used in user mode |
|
1.0 and |
CPU percentage used in system mode |
|
It is 0.0 |
Percentage of CPU occupied by user processes whose priority has been changed |
|
99.0 id |
percentage of idle cpu |
|
0.0 of |
Percentage of CPU occupied by processes waiting for input and output |
|
0.0 hi |
Percentage of CPU occupied by hard interrupt request service |
|
0.0 and |
Percentage of CPU occupied by softirq request service |
|
0.0 st |
steal time virtual world percentage, when there is a virtual machine, the percentage of time that the virtual cpu waits for the timing cpu |
ps: if the server has multiple cpus, multiple lines will be displayed
Fourth line: physical memory information
|
content |
illustrate |
|
KiB Mem: 1870784 total |
The total amount of physical memory, in KB |
|
720520 used |
Amount of physical memory used |
|
1150264 free |
Amount of free physical memory |
|
880 buffers |
Amount of memory as buffer |
Fifth line: swap partition information
|
Memory |
illustrate |
|
KiB Swap: 2097148 total |
Total size of swap partition (virtual memory) |
|
0 used |
The size of the used swap partition |
|
2097148 free |
The size of the free swap partition |
|
238616 cached Mem |
The size of the swap partition used as cache |
Sixth line: blank line
The seventh line: header information
|
content |
illustrate |
|
PID |
process id |
|
USER |
process owner |
|
PR |
Process priority |
|
IN |
Negative values indicate high priority, positive values indicate low priority |
|
VIRT |
The total amount of virtual memory used by the process, in kb. VIRT=SWAP RES |
|
RES |
The size of the physical memory used by the process but not swapped out, in kb. RES=CODE DATA |
|
SHR |
Shared memory size, in kb |
|
S |
Process status. D=uninterruptible sleep state R=running S=sleep T=track/stop Z=zombie process |
|
%CPU |
The percentage of CPU time used since the last update |
|
%MEM |
The percentage of physical memory used by the process |
|
TIME |
The total CPU time used by the process, in 1/100th of a second |
|
COMMAND |
Process name (command name/command line) |
2.7.3 pidof
Syntax: pidof [parameter] service name
Function description: Query the pid value of a specified service process
Case:
View the process id of the sshd service
[root@heimatengyun test]# pidof sshd
2962 2247
2.7.4 pstree
Syntax: pstree [options]
Function description: View process tree
Options:
-p: Display the PID of the process
Case:
[root@heimatengyun test]# pstree -p
systemd(1)─┬─ModemManager(948)─┬─{ModemManager}(1004)
│ └─{ModemManager}(1031)
├─NetworkManager(1123)─┬─{NetworkManager}(1284)
│ └─{NetworkManager}(1312)
...
2.7.5 kill
Syntax: kill [options] process id
Function description: Terminate a service process with a specified pid
Options:
-9: Force the process to stop immediately
Case:
[root@heimatengyun test]# kill -9 20385
2.7.6 killall
Syntax: killall [options] service name
Function description: Terminate all processes corresponding to a service with a specified name
Case:
Terminate all processes of the httpd service
[root@heimatengyun test]# killall httpd
2.8 System Status Detection Command
Use related commands to check the system status and resource consumption to ensure the healthy and stable operation of the system.
2.8.1 ifconfig
Syntax: ifconfig [network device] [parameters]
Function description: Get network card configuration and network status information
Case:
[root@heimatengyun test]# ifconfig
eno16777736: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.78.100 netmask 255.255.255.0 broadcast 192.168.78.255
inet6 fe80::20c:29ff:febc:5eef prefixlen 64 scopeid 0x20<link>
ether 00:0c:29:bc:5e:ef txqueuelen 1000 (Ethernet)
RX packets 143336 bytes 103106029 (98.3 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 92576 bytes 143399144 (136.7 MiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
Main view content: network card name (eno16777736), ip address (after inet), physical network card address, ie mac address (ether), number of packets received and sent by TX and TX, and cumulative traffic
2.8.2 netstat
Syntax: netstat [parameters]
Function description: Display the current network status of the entire system, such as current links, data packet transmission data, routing table content, etc.
Case:
[root@heimatengyun test]# netstat
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address Foreign Address State
tcp 0 96 192.168.78.100:ssh 192.168.78.1:59688 ESTABLISHED
Active UNIX domain sockets (w/o servers)
Proto RefCnt Flags Type State I-Node Path
unix 2 [ ] DGRAM 13149 /run/systemd/shutdownd
...
2.8.3 uname
Syntax: uname [options]
Function description: View information such as system kernel and system version
parameter:
-a:all Display complete system information
-s: kernel-name system kernel name
-n: nodename node name
-r: kernel-release kernel release
-v: kernel-version kernel version
-m: machine hardware name
-i: hardware-platform hardware platform
-p: processor processor type
-o: operating-system operating system name
Case:
[root@heimatengyun test]# uname
Linux
[root@heimatengyun test]# uname -a
Linux heimatengyun 3.10.0-123.el7.x86_64 #1 SMP Mon Jun 30 12:09:22 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
The displayed information is: kernel name (Linux), host name (heimatengyun), kernel release (3.10.0-123.el7.x86 64), kernel version (#1 SMP Mon Jun 30 12:09:22 UTC 2014) , hardware name (x86 64), hardware platform (x86 64), processor type (x86 64), and operating system name (GNU/Linux).
If you want to view the details of the single-signature system version, by viewing the /etc/redhat-release file
[root@heimatengyun test]# cat /etc/redhat-release
CentOS Linux release 7.0.1406 (Core)
2.8.4 uptime
Syntax: uptime [options]
Function description: View the load information of the system, which can display information such as the current system time, the system running time, the number of enabled terminals, and the average load value. The average load value refers to the pressure of the system in the last 1 minute, 5 minutes, and 15 minutes. The lower the load value, the better, try not to exceed 1 for a long time, and do not exceed 5 in the production environment.
Case:
[root@heimatengyun test]# uptime
21:30:44 up 1 day, 23:23, 3 users, load average: 0.00, 0.01, 0.05
2.8.5 free
Syntax: free [options]
Function description: Display the memory usage information in the current system
Options:
-m: megabytes display in megabytes
-h: human with unit output
Case:
[root@heimatengyun test]# free -h
total used free shared buffers cachedMem:
1.8G 702M 1.1G 8.9M 880K 233M
-/ buffers/cache: 468M 1.3GSwap: 2.0G 0B 2.0G
Field description: total (total memory), used (used), free (available), shared (memory shared by processes), buffers (disk cached memory), cached (cached memory)
2.8.5 who
Syntax: who [parameter]
Function description: View the user terminal information currently logged into the host
Case:
[root@heimatengyun test]# who
root pts/0 2019-11-22 22:10 (192.168.78.1)
root pts/1 2019-11-23 11:53 (192.168.78.1)
2.8.6 last
Syntax: last [parameter]
Function description: View all system login records. However, it should be noted that this information is saved in log files, so hackers can easily modify it, so this command cannot be used to judge whether there is hacking.
Case:
[root@heimatengyun test]# last
root pts/2 192.168.78.1 Sun Nov 24 13:09 - 13:36 (00:26)
root pts/1 192.168.78.1 Sat Nov 23 11:53 still logged in
...
2.8.7 history
Syntax: history [parameters]
Function description: Display the commands executed in history
Options:
-c: Clear all history, but .bash_history file contents will not be deleted
Case:
[root@heimatengyun test]# history
1 history
2 ll
3 ls
4 history
[root@heimatengyun test]# !2
ll
total 8
-rw-r--r--. 1 root root 26 Nov 23 20:40 test1.txt
-rw-r--r--. 1 root root 66 Nov 23 21:56 test.txt
You can use "!Number" to execute a command that has been executed once
1000 historical records can be viewed by default, but the value of HISTSIZE can be modified in /etc/profile
History commands are saved in a .bash_history file in a farmer's home directory (hidden files at the beginning of . are listed through ls or ll -a), which can be viewed with the cat command
2.9 Shutdown command
Linux is generally used on servers, and rarely encounters shutdowns. After all, the shutdown service will be interrupted, and it will be shut down unless there are special circumstances.
Correct shutdown process: sync>shutdown or reboot or halt
Regardless of restart or shutdown, you need to sync the memory data to the hard disk first to avoid data loss
2.9.1 reboot
Syntax: reboot [options]
Function description: Restart the system, equivalent to shutdown -r now
Case:
[root@heimatengyun ~]# reboot
2.9.2 poweroff
Syntax: poweroff [options]
Function description: Shut down the system
Case:
[root@heimatengyun ~]# poweroff
2.9.3 halt
Syntax: halt [options]
Function description: Shut down the system, equivalent to shutdown -h now and poweroff
Case:
[root@heimatengyun ~]# halt
2.9.4 shutdown
Syntax: shutdown [options] [shutdown time] [prompt content]
Function description: shutdown
Options:
-h: shutdown
-r: restart
Shutdown time:
hh:mm: Specifies the hour and minute in 24-hour clock to shut down
m: shutdown after m minutes (1: default, shutdown after 1 minute; 0: now, shutdown immediately)
Case:
Shut down after 1 minute and prompt all users logged into the system
[root@heimatengyun ~]# shutdown -h 1 "this server will shutdown after 1min"this server will shutdown after 1min
The system is going down for power-off at Sun 2019-11-24 22:25:55 CST!
User and file-related permission commands will be explained in future articles, and there are many other commands, which are not discussed here due to space limitations. The next article article will share "linux introductory series 6--rpm and yum repository for package management".
Original article, please indicate the source for reprinting：http://127.0.0.1:8000/system-administration-linux-tutorial/linux-commands-that-newbies-must-know/