📘 PAPER 5 – OPERATING SYSTEM (UNIT 4 – UNIX & LINUX COMMANDS) university of allahabad

 

🔴 UNIT 4 – UNIX & LINUX COMMANDS

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1️⃣ Introduction to UNIX / Linux

✅ UNIX

UNIX is a multi-user, multitasking operating system developed at AT&T Bell Labs.

✅ Linux

Linux is an open-source UNIX-based operating system.

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🔹 Features of Linux

✔ Open source
✔ Secure
✔ Portable
✔ Multi-user
✔ Multitasking

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2️⃣ Linux File System Structure

Directory	Purpose
/	Root directory
/bin	System commands
/etc	Configuration files
/home	User files
/usr	User programs
/var	Variable files
/tmp	Temporary files

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3️⃣ Basic Linux Commands

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📁 Directory Commands

Command	Description
pwd	Show current directory
ls	List files
cd	Change directory
mkdir	Create directory
rmdir	Remove empty directory

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📄 File Commands

Command	Description
touch	Create file
cat	View file
cp	Copy file
mv	Move/rename file
rm	Delete file
file	File type

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📘 Viewing Files

Command	Use
more	View page by page
less	Scrollable view
head	First 10 lines
tail	Last 10 lines

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4️⃣ File Permission Commands

Permission Types:

Symbol	Meaning
r	Read
w	Write
x	Execute

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Example:

-rwxr-xr--

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Change Permission:

chmod 755 file.txt

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5️⃣ Disk Related Commands

Command	Description
df	Disk free space
du	Disk usage
mount	Mount disk
umount	Unmount disk

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6️⃣ Process Management Commands

Command	Function
ps	Show running processes
top	Real-time process
kill	Kill process
nice	Set priority
sleep	Delay execution

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7️⃣ Input / Output Redirection

Symbols:

Symbol	Use
>	Output redirect
>>	Append
<	Input redirect
`	`

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Example:

ls > file.txt
cat file.txt | grep abc

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8️⃣ Background Processing

command &

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9️⃣ Process Scheduling Commands

Command	Purpose
at	Schedule job
cron	Repeated jobs
crontab	Cron table

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🔹 Example Cron Job:

* * * * * echo "Hello"

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🔟 File Editing Commands

Editors:

✔ vi
✔ vim
✔ nano

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vi Editor Modes:

1. Command mode

2. Insert mode

3. Exit mode

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Important vi Commands:

Command	Function
i	Insert
:w	Save
:q	Quit
:wq	Save & quit
dd	Delete line

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📌 EXAM IMPORTANT QUESTIONS (UNIT 4)

✔ Explain Linux file system
✔ Explain Linux commands
✔ File permission in Linux
✔ Explain I/O redirection
✔ Explain process management commands
✔ Explain cron & at