Tech-Notes

Linux Commands

1. Basic Commands
2. Folder and Directory Commands
3. File Commands
4. Variable Operations
5. File Permissions
6. Checksum and File Integrity Commands
7. File Compression
8. Process Management
9. Software Installation
10. Additional Commands

Linux commands are case sensitive

Basic commands

Command	Description
who am i	show the user
clear	to clear screen
cal	shows calender
cal 7 2018	shows particular month
cal feb 2018	shows particular month
date	print date details
date ‘+DATE:%m-%y%nTIME:%H:%M:%S’	print date in given format

Folder and Directory Commands

Command	Description
pwd	to view path directory
ls	list directoryt
la -l	detail list
ls -a	view all files (with hiddden files)
ls -la	view all files in list view
ls >list.txt	save that list content in a text file
cd..	back
cd name	enter in to a directory
mkdir name	make directory
rmdir name	remove directory

File Commands

File Command	Description
touch filename,txt	create a file
rm name	remove a file
//if space come in name	muthu\ rajesh.txt // it does not form as two separate files
cp filename1 filename2	copy
mv filename1 filename2	move
just give tab	autofill
grep requiredword file.txt	search word in file
diff file1.txt file2.txt	compare two files
passwrd	password

Variable Operations

Variable Command	Description
echo	print as it give next to it
name=rajesh	it becomes
$name	will give rajesh// syntax

File Permission

1. read = r
2. write = w
3. execute = x

User (u), Group (g), Others (o)(everyone)
Use chmod 0+w filename to add write permission.
For example, 754 means:

• 7 for User (u) - all permissions (read, write, execute)
• 5 for Group (g) - read and execute permissions
• 4 for Others (o) - read only.

chmod 754 filename is the syntax.

File Command	Description
4	stands for read
2	stands for write
1	stands for execute
0	stands for no
7	stands for all above

Checksum and file integrity commands:

Command	Description
sha256sum <filename>	Generates a SHA-256 checksum for the file (to verify integrity).
cat <filename>	` grep `	Checks if a file matches a specific checksum.

File compression

Command	Description
gzip <filename>	Compresses a file using gzip.
gunzip <filename>.gz	Decompresses a .gz file.
tar cvf <archive.tar> <file1> <file2>	Compresses multiple files into a .tar archive.
tar xvf <archive.tar>	Extracts files from a .tar archive.

Process Management

Command	Description
ctrl + z	Suspends the current process (move to background).
fg	Brings the suspended process to the foreground.
top	Shows real-time system process activity and resource usage.
ps aux	Displays detailed information about all running processes.
kill <pid>	Terminates a process by its process ID (PID).

Software Installation

Command	Description
sudo apt-get install <package_name>	Installs a new software package.
sudo apt-get update	Updates the package lists for upgrades and new packages.
sudo apt-get remove <package_name>	Uninstalls a software package.
<software_name> --version	Checks the version of installed software.

Additional Commands

Command	Description
df -h	Displays disk space usage in human-readable format.
du -sh <directory>	Shows the size of a directory.
ifconfig	Displays network configuration (IP addresses, etc.).
ping <hostname/IP>	Sends network packets to test connectivity.