What Is Linux?
Linux is an operating system's kernel. You might have heard of UNIX. Well, Linux is a UNIX clone. But it was actually created by Linus Torvalds from Scratch. Linux is free and open-source, that means that you can simply change anything in Linux and redistribute it in your own name! There are several Linux Distributions, commonly called “distros”.
- Ubuntu Linux
- Red Hat Enterprise Linux
- Linux Mint
- Debian
- Fedora
Linux is Mainly used in servers. About 90% of the internet is powered by Linux servers. This is because Linux is fast, secure, and free! The main problem of using Windows servers are their cost. This is solved by using Linux servers. The OS that runs in about 80% of the smartphones in the world, Android, is also made from the Linux kernel. Most of the viruses in the world run on Windows, but not on Linux!
Basic Linux commands
| Command |
Description |
|
ls |
Lists all files and directories in the present working directory |
ls -R |
Lists files in sub-directories as well |
ls -a |
Lists hidden files as well |
ls -al |
Lists files and directories with detailed information like permissions,size, owner, etc. |
cd or cd ~ |
Navigate to HOME directory |
cd .. |
Move one level up |
cd |
To change to a particular directory |
cd / |
Move to the root directory |
cat > filename |
Creates a new file |
cat filename |
Displays the file content |
cat file1 file2 > file3 |
Joins two files (file1, file2) and stores the output in a new file (file3) |
mv file "new file path" |
Moves the files to the new location |
mv filename new_file_name |
Renames the file to a new filename |
sudo |
Allows regular users to run programs with the security privileges of the superuser or root |
rm filename |
Deletes a file |
man |
Gives help information on a command |
history |
Gives a list of all past commands typed in the current terminal session |
clear |
Clears the terminal |
mkdir directoryname |
Creates a new directory in the present working directory or a at the specified path |
rmdir |
Deletes a directory |
mv |
Renames a directory |
pr -x |
Divides the file into x columns |
pr -h |
Assigns a header to the file |
pr -n |
Denotes the file with Line Numbers |
lp -nc , lpr c |
Prints “c” copies of the File |
lp-d lp-P
|
Specifies name of the printer |
apt-get
|
Command used to install and update packages |
mail -s 'subject'
-c 'cc-address'
-b 'bcc-address'
'to-address'
|
Command to send email |
mail -s "Subject"
to-address < Filename
|
Command to send email with attachment |
File Permission commands
| Command |
Description |
|
ls -l |
to show file type and access permission |
r |
read permission |
w |
write permission |
x |
execute permission |
-= |
no permission |
Chown user |
For changing the ownership of a file/directory |
Chown user:group filename |
change the user as well as group for a file or directory |
Environment Variables command
| Command |
Description |
|
echo $VARIABLE |
To display value of a variable |
env |
Displays all environment variables |
VARIABLE_NAME= variable_value |
Create a new variable |
Unset |
Remove a variable |
export Variable=value |
To set value of an environment variable |
User management commands of linux
| Command |
Description |
|
sudo adduser username |
To add a new user |
sudo passwd -l 'username' |
To change the password of a user |
sudo userdel -r 'username' |
To remove a newly created user |
sudo usermod -a -G GROUPNAME USERNAME |
To add a user to a group |
sudo deluser USER GROUPNAME |
To remove a user from a group |
finger |
Shows information of all the users logged in |
finger username |
Gives information of a particular user |
Networking command
| Command |
Description |
|
SSH username@ip-address or hostname |
login into a remote Linux machine using SSH |
Ping hostname="" or ="" |
To ping and Analyzing network and host connections |
dir |
Display files in the current directory of a remote computer |
cd "dirname" |
change directory to “dirname” on a remote computer |
put file |
upload ‘file’ from local to remote computer |
get file |
Download ‘file’ from remote to local computer |
quit |
Logout |
Process command
| Command |
Description |
|
bg |
To send a process to the background |
fg |
To run a stopped process in the foreground |
top |
Details on all Active Processes |
ps |
Give the status of processes running for a user |
ps PID |
Gives the status of a particular process |
pidof |
Gives the Process ID (PID) of a process |
kill PID |
Kills a process |
nice |
Starts a process with a given priority |
renice |
Changes priority of an already running process |
df |
Gives free hard disk space on your system |
free |
Gives free RAM on your system |
VI Editing Commands
| Command |
Description |
|
i |
Insert at cursor (goes into insert mode) |
a |
Write after cursor (goes into insert mode) |
A |
Write at the end of line (goes into insert mode) |
ESC |
Terminate insert mode |
u |
Undo last change |
U |
Undo all changes to the entire line |
o |
Open a new line (goes into insert mode) |
dd |
Delete line |
3dd |
Delete 3 lines |
D |
Delete contents of line after the cursor |
C |
Delete contents of a line after the cursor and insert new text. Press ESC key to end insertion. |
dw |
Delete word |
4dw |
Delete 4 words |
cw |
Change word |
x |
Delete character at the cursor |
r |
Replace character |
R |
Overwrite characters from cursor onward |
s |
Substitute one character under cursor continue to insert |
S |
Substitute entire line and begin to insert at the beginning of the line |
~ |
Change case of individual character |
Hope this Linux reference guide helps you!
