Basic Linux Commands
1. date
Print or set the system date and time
2. cal
Cal displays a simple calendar. If arguments are not specified, the current month is displayed.
3. Ctrl + l
Clear the screen.
4. pwd
Print name of current/working directory
5. cd
Command used to change directorycd / - Change directory to /
cd - - Present to Previous directory
cd - Switch to home directory
cd ~ student - Switch to the home directory of user student
cd .. - Switch one directory up
6. ls
List information about the FILEs (the current directory by default)
ls -a, --all
do not ignore entries starting with .
ls /proc
List all files under that directory.
7. rm
Remove files or directories
# rm -rf admincool - delete the directory admincool
# rm -v admincool - vrberose (background description)
# rm -rv * - remove all files in a folder
# rm -v *.mp3 - remove all mp3 extension files
# rm -v admincool2.txt - remove file admincool2.txt
# rm -rvf * - remove all contents in a folder recursively and forcefully
8. mkdir
Make directories
9. touch
Create an empty file
# touch admincool.txt admincool2.txt admincool3.txt admincool4.txt admincool5.txt - Create multiple files
10. cp
Copy files and directories.# cp Documents/temp/temp.txt Documents/temp1/
Copy temp.txt file from temp to temp1 folder.
11. mv
Move (rename) files. Rename SOURCE to DEST, or move SOURCE(s) to DIRECTORY.# mv Documents/temp1/temp.txt Documents/temp/temp2.txt
move temp.txt file from temp1 to temp folder and rename it as temp2.txt
12. vi
vi is a screen-oriented text editor originally created for the Unix operating system. The portable subset of the behavior of vi and programs based on it, and the ex editor language supported within these programs, is described by (and thus standardized by) the Single Unix Specification and POSIX.To Start vi
To use vi , type vi filename
# vi filename - edit filename starting at line 1
To Exit vi
:wq - Save and Quit
:q! - Quit without Save Chages
:q - quit (or exit) vi
:x - quit vi
Moving the Cursor
j or down-arrow - move cursor down one line
k or up-arrow - move cursor up one line
h or left-arrow - move cursor left one character
l or right-arrow - move cursor right one character
0 (zero) - move cursor to start of current line
$ - move cursor to end of current line
w - move cursor to beginning of next word
b - move cursor back to beginning of preceding word
Inserting or Adding Text
i - insert text before cursor, until hit 'EsC'
I - insert text at beginning of current line, until hit 'EsC'
a - add text after cursor, until hit 'EsC'
A - add text to end of current line, until hit 'EsC'
o - insert text in a new line below current line, until hit 'EsC'
O - insert text in a new line above current line, until hit 'EsC'
Deleting Text
D - delete the remainder of the line, starting with current cursor position
dd - delete entire current line
Copying and Pasting Text
yy - copies the current line
p - insert the copied text after the cursor
Searching Text
/string - search forward for occurrence of string in text
?string - search backward for occurrence of string in text
n - move to next occurrence of search string
N - move to next occurrence of search string in opposite direction
:500 - go to line no.500
13. ping
ping is a computer network administration software utility used to test the reachability of a host on an Internet Protocol (IP) network. It measures the round-trip time for messages sent from the originating host to a destination computer that are echoed back to the source.ping uses the ICMP protocol’s mandatory ECHO_REQUEST datagram to elicit an ICMP ECHO_RESPONSE from a host or gateway.ECHO_REQUEST datagrams (‘‘pings’’) have an IP and ICMP header, followed by a struct timeval
and then an arbitrary number of ‘‘pad’’ bytes used to fill out the packet.
# ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_seq=1 ttl=56 time=0.453 ms
64 bytes from 8.8.8.8: icmp_seq=2 ttl=56 time=0.462 ms
64 bytes from 8.8.8.8: icmp_seq=3 ttl=56 time=0.529 ms
64 bytes from 8.8.8.8: icmp_seq=4 ttl=56 time=0.483 ms
14. traceroute or tracepath
In computing, traceroute is a computer network diagnostic tool for displaying the route (path) and measuring transit delays of packets across an Internet Protocol (IP) network.# tracepath 8.8.8.8
1?: [LOCALHOST] pmtu 9001
1: ip-172-31-0-1.ap-south-1.compute.internal (172.31.0.1) 0.100ms pmtu 1500
1: no reply
2: no reply
3: no reply
4: 100.64.17.103 (100.64.17.103) 0.431ms
5: 52.95.67.211 (52.95.67.211) 1.274ms
6: 52.95.67.42 (52.95.67.42) 11.272ms asymm 9
7: 52.95.67.23 (52.95.67.23) 1.440ms
8: no reply
15. cat
Concatenate files and print on the standard output# cat admincool/admincool.txt - Display contents in admincool.txt
# cat > admincool/admincool.txt - Adding or overwriting file contents
# cat >> admincool/admincool.txt - Appending file contents
16. file
Determine file type# file admincool/admincool.txt
17. less
Test displating tool# less /var/log/messages - Display contents in page by page
<space> - next page
g - back
/pattern - search pattern
n - go to next pattern
q - quit
18. head
Display first 10 lines# head /var/log/messages
# head -n 20 /var/log/messages - Displays first 20 lines
19. tail
Display last 10 lines# tail /var/log/messages
# tail -n 20 /var/log/messages - Displays last 20 lines
20. grep
Pattern search# grep admin admincool/admincool.txt
21. top
top command will display Linux tasksThe top program provides a dynamic real-time view of a running system. It can display system summary information as well as a list of tasks currently being managed by the Linux kernel. The types of system summary information shown and the types, order and size of information displayed for tasks are all user configurable and that configuration can be made persistent across restarts.
22.vmstat
vmstat report virtual memory statisticsvmstat reports information about processes, memory, paging, block IO, traps, and cpu activity.
The first report produced gives averages since the last reboot. Additional reports give information on a sampling period of length delay. The process and memory reports are instantaneous in either case.
23. w
w show who is logged on and what they are doing.w displays information about the users currently on the machine, and their processes. The header shows, in this order, the current time, how long the system has been running, how many users are currently logged on, and the system load averages for the past 1, 5, and 15 minutes.
The following entries are displayed for each user: login name, the tty name, the remote host, login time, idle time, JCPU, PCPU, and the command line of their current process.
The JCPU time is the time used by all processes attached to the tty. It does not include past background jobs, but does include currently running background jobs.
The PCPU time is the time used by the current process, named in the "what" field.
24. who
who print information about users who are currently logged in
25. whoami
whoami print the user name associated with the current effective user ID
26. uptime
uptime tell how long the system has been runninguptime gives a one line display of the following information. The current time, how long the system has been running, how many users are currently logged on, and the system load averages for the past 1, 5, and 15 minutes.
27. free
Display amount of free and used memory in the system
28. ss
ss is a network monitoring utility,showing open,connected,listening portsss is used to dump socket statistics. It allows showing information similar to netstat. It can display more TCP and state informations than other tools.
29. netstat
Print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships
30. tcpdump
Dump traffic on a network. It is an online network monitoring utility
31. iostat
Report Central Processing Unit (CPU) statistics and input/output statistics for devices, partitions and network filesystems (NFS)
32. strace
trace system calls and signals# strace ls - Shows background process
33. iptraf
Interactive Colorful IP LAN Monitoriptraf is an ncurses-based IP LAN monitor that generates various network statistics including TCP info, UDP counts, ICMP and OSPF information, Ethernet load info, node stats, IP checksum errors, and others.
You need to install this package
# yum install iptraf
34. sar
Collect, report, or save system activity informationThe sar command writes to standard output the contents of selected cumulative activity counters in the operating system. The accounting system, based on the values in the count and interval parameters, writes information the specified number of times spaced at the specified intervals in seconds. If the interval parameter is set to zero, the sar command displays the average statistics for the time since the system was started. If the interval parameter is specified without the count parameter, then reports are generated continuously. The collected data can also be saved in the file specified by the -o filename flag, in addition to being displayed onto the screen. If filename is omitted, sar uses the standard system activity daily data file, the /var/log/sa/sadd file, where the dd parameter indicates the current day. By default all the data available from the kernel are saved in the data file.
35. nmap
Network exploration tool and security / port scanner, It shows open ports
36. wc
To count lines, words and characters of given file
# wc file_name
37. sort
To sort file in following order
-r Reverse normal order
-n Sort in numeric order
-nr Sort in reverse numeric order
# sort -r -n -nr filename
38. cmp
Compare two files byte by byte
# cmp file1 file2
39. diff
Compare files line by line
# diff file1 file2
40. pr
To print a file
# pr file_name
41. dmidecode
Linux Command to Retrieve Description of the System’s Hardware Components, Serial Numbers and BIOS Revision
# dmidecode -t system
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