Summary of some of my frequently used Linux commands

I worked in operations and maintenance for two years and used many commands. I deeply realized how much efficiency can be improved after mastering certain Linux commands. To give a simple example, after doing research and development, we often have to run some data. For the processing of the result data, our product colleagues are generally accustomed to using Excel to do statistics, copy the data into Excel, and then separate and sort the data... Finally, some simple conclusions are drawn. I only need cat, sort, uniq, awk, grep commands to complete the same operation in a blink of an eye.

Here I summarize some of the commands I have used in the past few years of work. Of course, I won’t mention simple commands such as vim cd ls mv cp. If you don’t know these commands, I suggest you learn them first. There are many commands here, I will just briefly list a few parameters that I commonly use. In fact, I don’t use many of these commands very often. In this article, I just want to let everyone know that there is such a tool. But if you want to learn more about its specific uses, I suggest you check the manual. I have also listed some reference materials for some comparison commands.

Server running status related commands

ps

To view the system process threads, I usually use this command to view the process pid, and then use the pid for more in-depth investigation.

Basic Usage

ps -aux to view all processes
ps -T -p ${pid} View the threads of a process

References
10 Important Linux ps Commands in Action

pstree

By viewing the system process tree, he can identify the relationship between each process using a tree structure.

Basic Usage
pstree

top

Check the running status of system process threads, usage of package resources, system load, etc. My usage is to see if the load on the server is very high, and then see which specific process and which thread occupies more CPU.

Basic Usage
top lists all thread load information
top -H lists the load information of all threads
top -H -p ${pid} lists the load information of all threads under a certain pid

free

Check memory and usage

Basic Usage
free

File operation related

cat

I always use this command to view configuration files or log files, but there is one thing to note: the cat command will output the entire file to the terminal. If the file content is very long, it is recommended to use grep to filter it, or directly use the less or more command.

Basic Usage
cat file.txt

tail
View the end of a file, or view the end of the standard output. The default value is 10 lines. You can use the -n parameter to specify the number of lines to output.

Basic Usage
tail -n 100 file.txt outputs the last 100 lines
tail -f file.txt As files are added, it continuously outputs the new content. It is generally used to view real-time logs.

head

It is very similar to the tail command, but head is used to output the header content. I personally feel that head is not used as much as tail command.

Basic Usage
head -n 100 file.txt outputs the first 100 lines

more

It is also used to view files, but the more command only loads one screen of content, which can be scrolled down. Because it loads less content, it is much faster than cat.

Basic Usage
more file.txt

less
It is very similar to more, but you can flip it up and down. I feel that less is enough for less and more. You can completely remove more.

Basic Usage
less file.txt

grep
This is a command I use very often, especially when troubleshooting, I need to use grep to filter out what I want from a large amount of data. grep also supports regular expression matching.

Basic Usage
grep "abc" file filters out the lines containing abc from file.

awk

As I said at the beginning, this command is one of my most commonly used commands. For example, when a file has multiple columns, I can use awk to output specific columns, or do some simple statistical summation, average, or do some simple data formatting.

Basic Usage
cat data | awk '{print $1,$3,$5}' outputs columns 1, 3, and 5. Note that the subscript starts at 1.
cat data | awk '{ sum += $1 } END { print sum }' sums the first column
cat data | awk -F'\t' '{print $1,$3}' Split each line of data into columns by tab and output 1 to 3 columns

References: Ruan Yifeng awk introduction

sort

Sort the standard content.

Basic Usage
cat file|sort Sort the data in file. Note that it is sorted in lexicographical order. If you want to sort by value, you need to add the -n parameter.
cat file|sort -k2 -n -r Sort in reverse order by the value of the second column, -k specifies the column, -r means reverse

uniq

De-duplicate the sorted content. Note that it only deduplicates adjacent and identical content, so if you want to deduplicate globally, you need to use sort first.

Basic Usage
cat file|sort|uniq Sort the files in file and remove duplicates
cat file|sort|uniq -c Sort the files in file and remove duplicates, and output the number of occurrences of each line

wc

I always use wc to count the number of lines. In fact, wc can not only count the number of lines, but also the number of words and characters.

Basic Usage
wc -l file counts the number of lines in the file
wc -w file how many words
wc -c file how many bytes
wc -m file how many characters

References
https://www.jb51.net/LINUXjishu/62056.html

sed

parallel

Most of the commands in Linux are single-process, and this command allows other commands to be executed in multiple processes.

References
15-minute introduction to GNU parallel

scp

In the past, when operating and maintaining a large number of machines, it was usually necessary to modify a configuration file in batches. All of these were done on one machine and then distributed to other machines using the scp script, which greatly improved efficiency.

Basic Usage
scp aaa.txt [email protected]:/tmp/ put the aaa.txt file in the current directory into the /tmp directory through the test account on 192.168.1.3
scp [email protected]:/tmp/aaa.txt . The opposite of the previous one

Disk and IO

du

View the size of the directory

Basic Usage
du -h --max-depth=1 outputs the directory with the deepest level, and then displays the file size in human-readable format, such as 1K 234M 2G

df

Check disk size and usage

Basic Usage
df -h View the size and usage of each partition

iostat

Check the disk io status

iotop

It can display the io status of each process in real time, similar to the top directory.

find

Search files by file name, file date, or file size. Very powerful. We previously had a server that forced deletion of files larger than 1G, older than 2 days, and with the file name *.log in a directory on the server when the disk was full. This was done using find plus xargs command

Basic Usage

find /home/test -iname "test.txt Find the file named test.txt in /home/test/, also supports wildcards
find /home/test -isize +100M Find files larger than 100M in /home/test

References
wikipedia unix find

locate

To locate a specific file, the locate command is much faster than find -name because it does not search a specific directory, but a database /var/lib/mlocate/mlocate.db. This database is updated regularly through a cron, so it is possible that newly created files cannot be retrieved.

Basic Usage
locate a.txt locates the location of a.txt. If there are multiple a.txt files in the system, all of them will be displayed.

tree

You can see the tree directory structure.

Basic Usage
tree -L 2 only displays two levels of tree structure

network

ping

Check whether the network is accessible

Basic Usage
ping www.baidu.com

nc

netcat can be used to see if a remote port is open. It is very powerful, but I don't use it much.

Basic Usage
nc -z xindoo.me 443 checks whether port 443 on my server is open (of course it is open)

References
Introduction to Linux nc command

route

View and manipulate the local routing table

Basic Usage
route lists the local routing table

References
route command

netstat

Check the network status of the machine to see the port occupancy and network link status.

Basic Usage
netstat -antp

traceroute

View all routing nodes that a request passes through to the target server, generally used to troubleshoot network problems.

Basic Usage
traceroute www.baidu.com

References

netstat Command

iftop

View real-time network io status

lsof

Check port usage

dig

Check the domain name information. When I was doing operation and maintenance before, I often needed to verify whether a domain name resolution change was effective. Because generally a domain name will be -A to multiple IPs, only one IP can be seen using the ping command. At this time, I would use dig to view the domain name resolution information.

Basic Usage
dig www.baidu.com

References
Introduction to dig command

curl

Initiate an http request. I usually use this command to verify whether the service can be accessed normally. It has the function of obtaining HTML source code.

Basic Usage
curl www.baidu.com
curl -I www.baidu.com Get the request header for baidu.com

References
How to use curl (English)

wget

To download a file from the Internet, there is basically a command line version of the download tool.

Basic Usage
wget xindoo.me/test.txt Download the test.txt file on my server to the local computer

other

yum|apt install

Many times the server does not have the tools we want, we can use this command to install them, yum is the Shell front-end package manager in Fedora, RedHat and CentOS, apt is on the Ubuntu platform.

Basic Usage
yum install curl
apt install curl

man

This command is used to view other command manuals, where you can see the detailed function and specific parameters of a specific command. This is a very important command. Generally, it is much more detailed than the --help provided by each command.

Basic Usage
man curl View the manual of the curl command

The above is the full content of this article. I hope it will be helpful for everyone’s study. I also hope that everyone will support 123WORDPRESS.COM.