# Top 23 Linux Commands YOU MUST KNOW ! Linux Operating System is used to run over 90% of all cloud infrastructure and hosting services. For this reason , it's important to be familiar with popular Linux command. I am a Junior Software Engineer , I am using Amazon Linux Machine for demonstration. Let’s get right into it! ## What Is a Linux Command? A Linux command is a program or utility that runs on the command line. A command line is an interface that accepts lines of text and processes them into instructions for your computer. *Before start discussing commands you should know following basic concepts:* * **Directory :** In Linux folder refers to directory. * **Arguments :** Argument is an input given as part of commands. *Syntax* ```bash ``` *Example* ```bash [ec2-user@ip-172-31-29-38 ~]$ cd GitDev [ec2-user@ip-172-31-29-38 GitDev]$ ls [ec2-user@ip-172-31-29-38 GitDev]$ touch code.py test.py [ec2-user@ip-172-31-29-38 GitDev]$ ls code.py test.py ``` Look at the above, command **cd GitDev** has changed our directory to **GitDev** and **touch code.py test.py** created two files for us. These are arguments which are inputs to commands. * **Options :** Options modify the default behavior of the command. Generally, they are used to change the output. *Example* ```bash [ec2-user@ip-172-31-29-38 GitDev]$ ls code.py test.py [ec2-user@ip-172-31-29-38 GitDev]$ ls -l total 0 -rw-r--r--. 1 ec2-user ec2-user 0 Mar 4 17:19 code.py -rw-r--r--. 1 ec2-user ec2-user 0 Mar 4 17:21 test.py [ec2-user@ip-172-31-29-38 GitDev]$ ls --inode 493092 code.py 493093 test.py ``` By default without option, the **ls** command lists the contents of the current directory. In the second command, we used the **\-l** option the command displays contents with their properties in a list format. When we use **\--inode** option in third the **ls** command, the command displays the **inode** number with the contents. * **Absolute Path** An absolute path is the location of a file or directory specified from the root working directory(/). Absolute path is complete path of file. *Example:* ```bash [ec2-user@ip-172-31-29-38 ~]$ ls /home/ec2-user/GitDev/ code.py test.py ``` In the above example we provided complete path **/home/ec2-user/GitDev/** of **GitDev** directory to list content of directory. * ***Relative Path*** Relative path is defined as path related to the current working directory. *Example :* ```bash [ec2-user@ip-172-31-29-38 ~]$ cd GitDev/ [ec2-user@ip-172-31-29-38 GitDev]$ ls code.py test.py ``` In the above example we are changing directory to **GitDev** using relative path **GitDev/.** There is no / before argument **GitDev** which indicates it’s a relative directory to present working directory. ### 1.pwd pwd command use to print the current working directory. ```bash [ec2-user@ip-172-31-29-38 ~]$ pwd /home/ec2-user ``` Here, my current working directory is **/home/ec2-user**. ### 2.ls ls command use to list the content of directory. ```bash [ec2-user@ip-172-31-29-38 GitDev]$ ls code.py test.py [ec2-user@ip-172-31-29-38 GitDev]$ ls -l total 0 -rw-r--r--. 1 ec2-user ec2-user 0 Mar 4 17:19 code.py -rw-r--r--. 1 ec2-user ec2-user 0 Mar 4 17:21 test.py ``` The **ls** command lists the contents of the **GitDev** directory. In the second command, we used the **\-l** option the command displays contents with their properties in a list format. ### 3.cd cd command use to change the directory: * Change directory to * Change directory to **home** (~) directory ```bash [ec2-user@ip-172-31-29-38 ~]$ pwd /home/ec2-user [ec2-user@ip-172-31-29-38 ~]$ cd ~ [ec2-user@ip-172-31-29-38 ~]$ pwd /home/ec2-user ``` * change directory to **parent** (..) directory ```bash [ec2-user@ip-172-31-29-38 ~]$ pwd /home/ec2-user [ec2-user@ip-172-31-29-38 ~]$ cd .. [ec2-user@ip-172-31-29-38 home]$ pwd /home ``` * change directory to **previous (-)** directory ```bash [ec2-user@ip-172-31-29-38 home]$ pwd /home [ec2-user@ip-172-31-29-38 home]$ cd - /home/ec2-user ``` ### 4.touch touch command use to create file without content. * ```bash [ec2-user@ip-172-31-29-38 GitDev]$ touch code.py test.py [ec2-user@ip-172-31-29-38 GitDev]$ ls code.py test.py ``` ### 5.cat cat command use to display the content o file. It is used to read the data from a file and gives its content as output. It also helps us to create, view, and concatenate files. ```bash [ec2-user@ip-172-31-29-38 ~]$ cat /etc/os-release NAME="Amazon Linux" VERSION="2023" ID="amzn" ID_LIKE="fedora" VERSION_ID="2023" PLATFORM_ID="platform:al2023" PRETTY_NAME="Amazon Linux 2023" ANSI_COLOR="0;33" CPE_NAME="cpe:2.3:o:amazon:amazon_linux:2023" HOME_URL="https://aws.amazon.com/linux/" BUG_REPORT_URL="https://github.com/amazonlinux/amazon-linux-2023" SUPPORT_END="2028-03-15" [ec2-user@ip-172-31-29-38 ~]$ ``` To concatenate several files, enter: ```bash [ec2-user@ip-172-31-29-38 GitDev]$ touch dev1.py dev2.py [ec2-user@ip-172-31-29-38 GitDev]$ ls code.py dev1.py dev2.py test.py [ec2-user@ip-172-31-29-38 GitDev]$ cat dev1.py dev2.py > final.py [ec2-user@ip-172-31-29-38 GitDev]$ ls code.py dev1.py dev2.py final.py test.py ``` This command creates a file named **final.py** that is a copy of **dev1.py** followed by **dev2.py** ### 6.mkdir mkdir command use to create new directory in the current working directory. The mkdir command allows you to create directories from within the terminal. The default syntax is **mkdir** followed by the directory name. ```bash [ec2-user@ip-172-31-29-38 ~]$ mkdir GitDev [ec2-user@ip-172-31-29-38 ~]$ ls GitDev ``` You can see ,we have created the **GitDev** directory. ### 7.cp cp command use to copy files and directories from source to desired destination. * **Copying Files** The following are examples of coping files * To make copy of file withing the current directory ```bash [ec2-user@ip-172-31-29-38 GitDev]$ cp code.py copy_code.py [ec2-user@ip-172-31-29-38 GitDev]$ ls code.py copy_code.py dev1.py dev2.py final.py test.py ``` This created copy of **code.py** file as **copy\_code.py** * To copy a file in your current directory into another directory ```bash [ec2-user@ip-172-31-29-38 ~]$ cp main.py /home/ec2-user/GitDev [ec2-user@ip-172-31-29-38 ~]$ cd GitDev/ [ec2-user@ip-172-31-29-38 GitDev]$ ls code.py copy_code.py dev1.py dev2.py final.py main.py test.py ``` This copied main.py file from current directory to **/home/ec2-user/GitDev** directory * To copy all the files in a directory to a new directory ```bash [ec2-user@ip-172-31-29-38 ~]$ cp GitDev/* GitTest [ec2-user@ip-172-31-29-38 ~]$ cd GitTest/ [ec2-user@ip-172-31-29-38 GitTest]$ ls code.py copy_code.py dev1.py dev2.py final.py main.py test.py ``` This copied all files from **GitDev** directory to **GitTest** directory. * **Copying Directory** To copy all the files from source directory to destination directory ```bash [ec2-user@ip-172-31-29-38 ~]$ cp -r GitDev GitTest [ec2-user@ip-172-31-29-38 ~]$ cd GitTest/ [ec2-user@ip-172-31-29-38 GitTest]$ ls code.py copy_code.py dev1.py dev2.py final.py main.py test.p ``` ### 8.mv **mv** command use to **move** files and directories from one directory to another or to **rename** a file or directory * **Move files** ```bash [ec2-user@ip-172-31-29-38 ~]$ mv final.py GitDev/ [ec2-user@ip-172-31-29-38 GitDev]$ ls final.py ``` Here, we moved **final.py** to **GitDev.** Use **\-r**(recursively) option to move files more than one. * **Rename file** ```bash [ec2-user@ip-172-31-29-38 ~]$ mv main.py new_name.py [ec2-user@ip-172-31-29-38 ~]$ ls new_name.py ``` Here, we renamed **main.py** to **new\_name.py** ### 9.rm **rm** use to delete file from current ```bash [ec2-user@ip-172-31-29-38 ~]$ ls GitDev GitTest main.py [ec2-user@ip-172-31-29-38 ~]$ rm main.py [ec2-user@ip-172-31-29-38 ~]$ ls GitDev GitTest ``` To delete all the files in the mydir directory, one by one, type the following: ```bash [ec2-user@ip-172-31-29-38 ~]$ cd GitDev/ [ec2-user@ip-172-31-29-38 GitDev]$ ls code.py copy_code.py dev1.py dev2.py final.py main.py test.py [ec2-user@ip-172-31-29-38 GitDev]$ cd .. [ec2-user@ip-172-31-29-38 ~]$ rm -i GitDev/* rm: remove regular empty file 'GitDev/code.py'? y rm: remove regular empty file 'GitDev/copy_code.py'? yy rm: remove regular empty file 'GitDev/dev1.py'? y rm: remove regular empty file 'GitDev/dev2.py'? y rm: remove regular empty file 'GitDev/final.py'? y rm: remove regular empty file 'GitDev/main.py'? y rm: remove regular empty file 'GitDev/test.py'? y [ec2-user@ip-172-31-29-38 ~]$ cd GitDev/ [ec2-user@ip-172-31-29-38 GitDev]$ ls ``` After each file name displays, type y and press Enter to delete the file. ### 10.rmdir rmdir command uses to delete directory. * **Remove empty directory***GitDev* ```bash [ec2-user@ip-172-31-29-38 ~]$ rmdir GitDev/ [ec2-user@ip-172-31-29-38 ~]$ ls GitTest ``` * **Remove non empty directory***GitTest* ```bash [ec2-user@ip-172-31-29-38 ~]$ rmdir -r GitTest/ [ec2-user@ip-172-31-29-38 ~]$ ls ``` ### 12\. find find command use to find the file in directory. Syntax : *find directory\_path -name file\_name* Here directory\_path is path of directory where you want search file. ```bash ec2-user@ip-172-31-28-71 ~]$ find . -name main.py ./GitDev/main.py ``` In the above command searches file main.py in current directory. ```bash [ec2-user@ip-172-31-28-71 ~]$ find . -name *.py ./GitDev/main.py ./GitDev/test.py ``` In the above command searches all the which file name ends with .py in current directory. ### 13.grep grep command use to search lines in file matching pattern. ```bash [ec2-user@ip-172-31-28-71 ~]$ cat main.py # This program adds two numbers num1 = 1.5 num2 = 6.3 # Add two numbers sum = num1 + num2 # Display the sum print('The sum of {0} and {1} is {2}'.format(num1, num2, sum)) [ec2-user@ip-172-31-29-58 ~]$ grep -i "num" main.py # This program adds two numbers num1 = 1.5 num2 = 6.3 # Add two numbers sum = num1 + num2 print('The sum of {0} and {1} is {2}'.format(num1, num2, sum)) [ec2-user@ip-172-31-29-58 ~]$ grep -c "num" main.py 6 ``` The -i option enables to search for a string case insensitively in the given file. It matches the words "num" ,"num1", "num2". We can find the number of lines that matches the given string/pattern using option -c. ### 14.awk awk command use for pattern search and processing. What operations awk command can do? * Scanning files line by line * Splitting each input line into fields * Comparing input lines and fields to patterns * Performing specified actions on matching lines ```bash [ec2-user@ip-172-31-28-71 ~]$ cat main.py # This program adds two numbers num1 = 1.5 num2 = 6.3 # Add two numbers sum = num1 + num2 # Display the sum print('The sum of {0} and {1} is {2}'.format(num1, num2, sum)) [ec2-user@ip-172-31-29-58 ~]$ awk '/num/ {print}' main.py # This program adds two numbers num1 = 1.5 num2 = 6.3 # Add two numbers sum = num1 + num2 print('The sum of {0} and {1} is {2}'.format(num1, num2, sum)) [ec2-user@ip-172-31-29-58 ~]$ awk '{print $1,$4}' main.py # adds num1 num2 # numbers sum + # sum print('The {0} ``` awk '/num/ {print}' [main.py](http://main.py) this prints the lines which match the given pattern. awk '{print $1,$4}' main.py splitting a line into two fields $1 and $4. ### 15.df df command is used to see the storage usage by different file system directories (technical term here is file system mounts).This displays information about total space and available space on a file system. ```bash [ec2-user@ip-172-31-28-71 ~]$ df Filesystem 1K-blocks Used Available Use% Mounted on devtmpfs 4096 0 4096 0% /dev tmpfs 486172 0 486172 0% /dev/shm tmpfs 194472 2880 191592 2% /run /dev/xvda1 8310764 1591284 6719480 20% / tmpfs 486172 0 486172 0% /tmp /dev/xvda128 10202 1310 8892 13% /boot/efi tmpfs 97232 0 97232 0% /run/user/1000 ``` ### 16.du du command use to print disk usage in MB Gb. This displays the number of blocks used for files. Exit Status: This command returns the following exit values: | **Item** | **Description** | | --- | --- | | **0** | Successful completion. | | **\>0** | An error occurred. | ```bash [ec2-user@ip-172-31-28-71 ~]$ du 4 ./.ssh 12 ./GitDev 36 . ``` This displays the number of disk blocks in the current directory and each of its subdirectories. ### 17.lscpu lscpu command use to print CPU information. The lscpu command in Linux with the `-J` argument generates the output in JSON format. ```bash [ec2-user@ip-172-31-28-71 ~]$ lscpu -J { "lscpu": [ { "field": "Architecture:", "data": "x86_64", "children": [ { "field": "CPU op-mode(s):", "data": "32-bit, 64-bit" },{ "field": "Address sizes:", "data": "46 bits physical, 48 bits virtual" },{ "field": "Byte Order:", "data": "Little Endian" } ] } MORE ``` ### 18.ps ps command use to get the information of processes. Processes need system resources like CPU, Physical memory etc. to stay alive.ps is a powerful tool that allows you to view information about the processes running on your Linux system. It helps monitor running processes, identify process ID (**PID**), terminal type (**TTY**), **CPU** time usage, command name, user ID and other information. * ***ps -ef or ps -aux****− List currently running processes in full format* ```bash [ec2-user@ip-172-31-28-71 ~]$ ps -ef UID PID PPID C STIME TTY TIME CMD root 1 0 0 Mar06 ? 00:00:05 /usr/lib/systemd/systemd --switched-root --system --deserialize=32 root 2 0 0 Mar06 ? 00:00:00 [kthreadd] root 3 2 0 Mar06 ? 00:00:00 [rcu_gp] root 4 2 0 Mar06 ? 00:00:00 [rcu_par_gp] root 5 2 0 Mar06 ? 00:00:00 [slub_flushwq] root 6 2 0 Mar06 ? 00:00:00 [netns] MORE ``` ### 19.Kill Kill command use to kill process. Syntax : kill -9 process\_id or process\_name ```bash [ec2-user@ip-172-31-28-71 ~]$ ps -ef | grep http root 59143 1 0 16:57 ? 00:00:00 /usr/sbin/httpd -DFOREGROUND apache 59164 59143 0 16:57 ? 00:00:00 /usr/sbin/httpd -DFOREGROUND apache 59165 59143 0 16:57 ? 00:00:00 /usr/sbin/httpd -DFOREGROUND apache 59166 59143 0 16:57 ? 00:00:00 /usr/sbin/httpd -DFOREGROUND apache 59167 59143 0 16:57 ? 00:00:00 /usr/sbin/httpd -DFOREGROUND ec2-user 62502 38348 0 17:03 pts/0 00:00:00 grep --color=auto http [ec2-user@ip-172-31-28-71 ~]$ sudo kill -9 59164 [ec2-user@ip-172-31-28-71 ~]$ ``` This kills process apache which has process id 59143. You can get process ids from ps command. ### 20.netstat netstat  -an command that there’s indeed a process listening on ports. This command helps to check things about how your computer connects to the internet. netstat stands for network statistics. ```bash [ec2-user@ip-172-31-29-58 ~]$ netstat -a | more Active Internet connections (servers and established) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 0.0.0.0:ssh 0.0.0.0:* LISTEN tcp 0 0 ip-172-31-29-58.us-:ssh ec2-18-237-140-16:52390 ESTABLISHED tcp6 0 0 [::]:ssh [::]:* LISTEN udp 0 0 ip-172-31-29-58.:bootpc 0.0.0.0:* udp 0 0 localhost:323 0.0.0.0:* udp6 0 0 ip-172-31:dhcpv6-client [::]:* udp6 0 0 localhost6:323 [::]:* raw6 0 0 [::]:ipv6-icmp [::]:* 7 Active UNIX domain sockets (servers and established) Proto RefCnt Flags Type State I-Node Path unix 3 [ ] STREAM CONNECTED 18595 unix 3 [ ] STREAM CONNECTED 18690 /run/systemd/journal/stdout unix 3 [ ] STREAM CONNECTED 16002 unix 2 [ ACC ] STREAM LISTENING 14501 /run/systemd/resolve/io.systemd.Resolve unix 2 [ ACC ] STREAM LISTENING 14506 /run/systemd/resolve/io.systemd.Resolve.Monitor --More-- ``` netstat -a | more show both listening and non-listening sockets. With the –interfaces option, show interfaces that are not up. ### 21.ifconfig ifconfig command find the IP addresses. Configures or displays network interface parameters for a network by using TCP/IP. ```bash [ec2-user@ip-172-31-28-71 ~]$ ifconfig enX0: flags=4163 mtu 9001 inet 172.31.28.71 netmask 255.255.240.0 broadcast 172.31.31.255 inet6 fe80::49:54ff:fec4:c79d prefixlen 64 scopeid 0x20 ether 02:49:54:c4:c7:9d txqueuelen 1000 (Ethernet) RX packets 48407 bytes 32785275 (31.2 MiB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 31357 bytes 3158831 (3.0 MiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 lo: flags=73 mtu 65536 inet 127.0.0.1 netmask 255.0.0.0 inet6 ::1 prefixlen 128 scopeid 0x10 loop txqueuelen 1000 (Local Loopback) RX packets 12 bytes 1020 (1020.0 B) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 12 bytes 1020 (1020.0 B) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 [ec2-user@ip-172-31-28-71 ~]$ ``` ### 22.tcpdump tcpdump command can be used to find all communications (aka network packages) happening through your network (coming in or going out of your machine) ### 23.ping ping is a network utility tool and helps to check if a particular IP address is reachable ```bash [ec2-user@ip-172-31-28-71 ~]$ ping google.com PING google.com (142.250.217.110) 56(84) bytes of data. 64 bytes from sea09s30-in-f14.1e100.net (142.250.217.110): icmp_seq=1 ttl=58 time=7.77 ms 64 bytes from sea09s30-in-f14.1e100.net (142.250.217.110): icmp_seq=2 ttl=58 time=7.82 ms 64 bytes from sea09s30-in-f14.1e100.net (142.250.217.110): icmp_seq=3 ttl=58 time=7.90 ms 64 bytes from sea09s30-in-f14.1e100.net (142.250.217.110): icmp_seq=4 ttl=58 time=7.87 ms 64 bytes from sea09s30-in-f14.1e100.net (142.250.217.110): icmp_seq=5 ttl=58 time=7.86 ms 64 bytes from sea09s30-in-f14.1e100.net (142.250.217.110): icmp_seq=6 ttl=58 time=7.79 ms 64 bytes from sea09s30-in-f14.1e100.net (142.250.217.110): icmp_seq=7 ttl=58 time=7.83 ms 64 bytes from sea09s30-in-f14.1e100.net (142.250.217.110): icmp_seq=8 ttl=58 time=7.82 ms ^C --- google.com ping statistics --- 8 packets transmitted, 8 received, 0% packet loss, time 7012ms rtt min/avg/max/mdev = 7.769/7.832/7.900/0.040 ms [ec2-user@ip-172-31-28-71 ~]$ ping git.com PING git.com (44.233.224.228) 56(84) bytes of data. ^C --- git.com ping statistics --- 56 packets transmitted, 0 received, 100% packet loss, time 57168ms [ec2-user@ip-172-31-28-71 ~]$ ```