Linux

Linux Commands Cheatsheet – 2020 Update

Linux is becoming well known because it’s more than just free software as it’s unusually a good operating system. Linux was first developed by Linus Torvalds at the University of Helsinki in Finland.

If you’ve never worked with Linux before, you may be confused as to why there are so many different versions of it available. Linux commands are not the same as standard Unix ones. Most of the commands are provided by the GNU project.

Back before the days of graphical desktops, the only way to interact with a Unix system was through a text command line interface (CLI) provided by the shell. The CLI allowed text input only, and could only display text and rudimentary graphics output.

If you’re just beginning to work on a Linux system in this year (2020), the abundance of commands might prove daunting. To help, the following lists present a sampling of commands on various topics such as Networking, File Management, Programming etc.

S.No Commands Description
1 uname -a Display Linux system information
2 uname -r Display kernel release information
3 cat /etc/redhat-release Show which version of redhat installed
4 uptime Show how long the system has been running + load
5 hostname Show system host name
6 hostname -I Display the IP addresses of the host
7 last reboot Show system reboot history
8 date Show the current date and time
9 cal Show this month’s calendar
10 w Display who is online
11 whoami Who you are logged in as
12 dmesg Display messages in kernel ring buffer
13 cat /proc/cpuinfo Display CPU information
14 cat /proc/meminfo Display memory information
15 free -h Display free and used memory ( -h for human readable, -m for MB, -g for GB.)
16 lspci -tv Display PCI devices
17 lsusb -tv Display USB devices
18 dmidecode Display DMI/SMBIOS (hardware info) from the BIOS
19 hdparm -i /dev/sda Show info about disk sda
20 hdparm -tT /dev/sda Perform a read speed test on disk sda
21 badblocks -s /dev/sda Test for unreadable blocks on disk sda
22 top Display and manage the top processes
23 htop Interactive process viewer (top alternative)
24 mpstat 1 Display processor related statistics
25 vmstat 1 Display virtual memory statistics
26 iostat 1 Display I/O statistics
27 tail 100 /var/log/messages Display the last 100 syslog messages (Use /var/log/syslog for Debian based systems.)
28 tcpdump -i eth0 Capture and display all packets on interface eth0
29 tcpdump -i eth0 ‘port 80’ Monitor all traffic on port 80 ( HTTP )
30 lsof List all open files on the system
31 lsof -u user List files opened by user
32 free -h Display free and used memory ( -h for human readable, -m for MB, -g for GB.)
33 watch df -h Execute “df -h”, showing periodic updates
34 id Display the user and group ids of your current user.
35 last Display the last users who have logged onto the system.
36 who Show who is logged into the system.
37 w Show who is logged in and what they are doing.
38 groupadd test Create a group named “test”.
39 useradd -c “John Smith” -m john Create an account named john, with a comment of “John Smith” and create the user’s home directory.
40 userdel john Delete the john account.
41 usermod -aG sales john Add the john account to the sales group
42 ls -al List all files in a long listing (detailed) format
43 pwd Display the present working directory
44 mkdir directory Create a directory
45 rm file Remove (delete) file
46 rm -r directory Remove the directory and its contents recursively
47 rm -f file Force removal of file without prompting for confirmation
48 rm -rf directory Forcefully remove directory recursively
49 cp file1 file2 Copy file1 to file2
50 cp -r source_directory destination Copy source_directory recursively to destination. If destination exists, copy
source_directory into destination, otherwise create destination with the contents of source_directory.
51 mv file1 file2 Rename or move file1 to file2. If file2 is an existing directory, move file1 into directory file2
52 ln -s /path/to/file linkname Create symbolic link to linkname
53 touch file Create an empty file or update the access and modification times of file.
54 cat file View the contents of file
55 less file Browse through a text file
56 head file Display the first 10 lines of file
57 tail file Display the last 10 lines of file
58 tail -f file Display the last 10 lines of file and “follow” the file as it grows.
59 ps Display your currently running processes
60 ps -ef Display all the currently running processes on the system.
61 ps -ef | grep processname Display process information for processname
62 top Display and manage the top processes
63 htop Interactive process viewer (top alternative)
64 kill pid Kill process with process ID of pid
65 killall processname Kill all processes named processname
66 program & Start program in the background
67 bg Display stopped or background jobs
68 fg Brings the most recent background job to foreground
69 fg n Brings job n to the foreground
70 ifconfig -a Display all network interfaces and ip address
71 ifconfig eth0 Display eth0 address and details
72 ethtool eth0 Query or control network driver and hardware settings
73 ping host Send ICMP echo request to host
74 whois domain Display whois information for domain
75 dig domain Display DNS information for domain
76 dig -x IP_ADDRESS Reverse lookup of IP_ADDRESS
77 host domain Display DNS ip address for domain
78 hostname -i Display the network address of the host name.
79 hostname -I Display all local ip addresses
80 wget http://domain.com/file Download http://domain.com/file
81 netstat -nutlp Display listening tcp and udp ports and corresponding programs
82 tar cf archive.tar directory Create tar named archive.tar containing directory.
83 tar xf archive.tar Extract the contents from archive.tar.
84 tar czf archive.tar.gz directory Create a gzip compressed tar file name archive.tar.gz.
85 tar xzf archive.tar.gz Extract a gzip compressed tar file.
86 tar cjf archive.tar.bz2 directory Create a tar file with bzip2 compression
87 tar xjf archive.tar.bz2 Extract a bzip2 compressed tar file.
88 yum search keyword Search for a package by keyword.
89 yum install package Install package.
90 yum info package Display description and summary information about package.
91 rpm -i package.rpm Install package from local file named package.rpm
92 yum remove package Remove/uninstall package.
93 tar zxvf sourcecode.tar.gz
cd sourcecode
./configure
make
make install
Install software from source code.
94 grep pattern file Search for pattern in file
95 grep -r pattern directory Search recursively for pattern in directory
96 locate name Find files and directories by name
97 find /home/john -name ‘prefix*’ Find files in /home/john that start with “prefix”.
98 find /home -size +100M Find files larger than 100MB in /home
99 ssh host Connect to host as your local username.
100 ssh user@host Connect to host as user
101 ssh -p port user@host Connect to host using port
102 scp file.txt server:/tmp Secure copy file.txt to the /tmp folder on server
103 scp server:/var/www/*.html /tmp Copy *.html files from server to the local /tmp folder.
104 scp -r server:/var/www /tmp Copy all files and directories recursively from server to the current system’s /tmp folder.
105 rsync -a /home /backups/ Synchronize /home to /backups/home
106 df -h Show free and used space on mounted filesystems
107 df -i Show free and used inodes on mounted filesystems
108 fdisk -l Display disks partitions sizes and types
109 du -ah Display disk usage for all files and directories in human readable format
110 du -sh Display total disk usage off the current directory
111 cd .. To go up one level of the directory tree. (Change into the parent directory.)
112 cd Go to the $HOME directory
113 cd /etc Change to the /etc directory

Reference

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