Linux

Putty

• Windows to Linux Connection Achived through Putty. Logs & Monitoring System Monitoring Commands varghese@DESKTOP-OODIU93:/Data$ top top - 13:42:11 up 12 min, 0 users, load average: 0.13, 0.63, 0.61 Tasks: 40 total, 1 running, 39 sleeping, 0 stopped, 0 zombie %Cpu(s): 0.4 us, 0.5 sy, 0.0 ni, 98.9 id, 0.0 wa, 0.0 hi, 0.2 si, 0.0 st MiB Mem : 3881.2 total, 2825.8 free, 418.2 used, 637.3 buff/cache MiB Swap: 1024.0 total, 1024.0 free, 0.0 used. 3314.1 avail Mem varghese@DESKTOP-OODIU93:/Data$ free -m total used free shared buff/cache available Mem: 3881 418 2825 14 637 3314 Swap: 1024 0 1024 varghese@DESKTOP-OODIU93:/Data$ vmstat procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu----- r b swpd free buff cache si so bi bo in cs us sy id wa st 0 2 0 2825464 108436 595640 0 0 147 10 106 125 1 1 74 24 0 varghese@DESKTOP-OODIU93:/Data$ iostat Linux 6.6.87.2-microsoft-standard-WSL2 (DESKTOP-OODIU93) 03/14/26 x86_64 (4 CPU)

avg-cpu: %user %nice %system %iowait %steal %idle 0.91 0.00 1.14 20.60 0.00 77.34

Device tps kB_read/s kB_wrtn/s kB_dscd/s sda 1.18 77.30 0.00 0.00 sdb 0.16 11.53 0.00 0.00 sdc 0.11 2.97 0.00 0.00 sdd 25.52 381.53 32.45 21.93 Log Files in Linux

Most system and application logs are stored in the /var/log directory.

varghese@DESKTOP-OODIU93:~/Data$ cd /var varghese@DESKTOP-OODIU93:/var$ ls -lrt

Important directories inside /var:

/var/log /var/cache /var/tmp /var/backups /var/www Log Directory varghese@DESKTOP-OODIU93:/var$ cd log varghese@DESKTOP-OODIU93:/var/log$ ls

Example log files:

alternatives.log auth.log dmesg dpkg.log kern.log syslog apache2/ journal/ Important Log Files

1. dmesg (Kernel Messages)

Shows kernel boot messages and hardware events.

varghese@DESKTOP-OODIU93:/var/log$ cat dmesg

Example:

[ 0.000000] kernel: Linux version 6.6.87.2-microsoft-standard-WSL2 [ 0.000000] kernel: Command line: initrd=\initrd.img WSL_ROOT_INIT=1

Used for:

Hardware detection

Kernel boot messages

Driver issues

System startup troubleshooting

2. syslog (System Logs)

Shows system activities and background services like cron jobs.

varghese@DESKTOP-OODIU93:/var/log$ cat syslog

Example:

Mar 8 17:49:59 DESKTOP-OODIU93 systemd[1]: rsyslog.service: Sent signal SIGHUP

Used for:

System events

Service logs

Scheduled jobs

Error tracking

Apache Logs

Apache web server logs are stored in:

/var/log/apache2/ varghese@DESKTOP-OODIU93:/var/log$ cd apache2/ varghese@DESKTOP-OODIU93:/var/log/apache2$ ls

Example:

access.log error.log error.log.1 other_vhosts_access.log access.log

Records all client requests to the web server.

error.log

Stores Apache server errors and warnings.

Summary

Important monitoring commands:

Command Purpose top Real-time CPU and process monitoring free -m Memory usage vmstat System performance statistics iostat Disk I/O statistics

Important log files:

Log File Purpose dmesg Kernel and hardware events syslog System and service logs auth.log Authentication logs kern.log Kernel logs apache2/* Apache web server logs

Note: dmesg and syslog are both very important for Logs & Monitoring, especially for troubleshooting system issues and tracking events.

Corn Job Scheduler (Sample)

• Corn Format in Linux Cmd_IMG & Below both are same

• • • • • command-to-execute

---

| | | | | | | | | +---- Day of the Week (0 - 7, where both 0 and 7 are Sunday) | | | +------ Month (1 - 12) | | +-------- Day of the Month (1 - 31) | +---------- Hour (0 - 23) +------------ Minute (0 - 59)

Guide: Automating a Script with CronStep 1: Create the Shell ScriptCreate a file named script.sh in your home directory. This script contains the actual task you want to perform.File: /home/varghese/script.shBash#!/bin/bash

This line appends the current date and time to a log file

echo "Test $(date)" >> /home/varghese/test_log.txt Note: Ensure the script is executable by running: chmod +x /home/varghese/script.shStep 2: Configure the Cron TableOpen your user's crontab configuration to schedule the task.Command:Bashcrontab -e Inside the editor (GNU nano):Scroll to the very bottom and add the following line. This tells the system to run your script every minute (* * * * *).Plaintext# m h dom mon dow command

• • • • • /bin/bash /home/varghese/script.sh Press Ctrl + O, Enter to save, and Ctrl + X to exit.Step 3: Verify the OutputWait at least 60 seconds for the first cycle to trigger. Then, check the log file to see if the script is running automatically.Command:Bashcat /home/varghese/test_log.txt Expected Output:PlaintextTest Tue Mar 10 13:00:01 EDT 2026 Test Tue Mar 10 13:01:01 EDT 2026 Test Tue Mar 10 13:02:01 EDT 2026 Summary of Key CommandsActionCommandEdit Cron Jobscrontab -eList Active Jobscrontab -lMake Script Executablechmod +x script.shCheck Script Manually./script.sh

1️⃣ Apache Service Management

You successfully installed and managed Apache HTTP Server. Below is a clean summary of the commands you used.

Check Apache Status sudo systemctl status apache2

Output shows:

Active: running

Apache processes running (/usr/sbin/apache2 -k start)

This confirms the web server is working.

Start Apache sudo systemctl start apache2

Starts the Apache service.

Stop Apache sudo systemctl stop apache2

Stops the Apache web server.

Restart Apache sudo systemctl restart apache2

Restarts Apache after configuration changes.

Enable Apache at Boot sudo systemctl enable apache2

Automatically starts Apache when the system boots.

Disable Apache at Boot sudo systemctl disable apache2

Prevents Apache from starting automatically.

Access Apache in Browser

Open:

http://localhost

or

http://127.0.0.1

Default web directory in Ubuntu:

/var/www/html 2️⃣ Storage Management & Disk Information Check Disk Usage df -h

Example output:

Filesystem Size Used Available Use% Mounted /dev/sdd 1TB 4GB 952GB 1% /

-h = human readable format.

Show Block Devices lsblk

Output explanation:

Device Type Size Mount sda disk 388.6M system sdb disk 186M system sdc swap 1G swap sdd disk 1TB main filesystem Install Disk Partition Tool sudo apt install fdisk

Installs the fdisk utility.

View Disk Partitions sudo fdisk -l

Shows:

Disk size

Sector size

Partition layout

Example:

Disk Size Sectors /dev/sdd 1TB 2147483648 3️⃣ Important Notes

You are running Ubuntu inside Windows Subsystem for Linux.

Because of this:

Apache runs inside Linux

Browser runs in Windows

So access Apache using:

http://localhost

from the Windows browser.

Linux Commands Notes

1. File Permissions Change File Permission chmod u=rwx,g=rwx,o=r script1.sh

Check permissions:

ls -l script1.sh

Output:

-rwxrwxr-- 1 varghese varghese 17 Mar 3 12:36 script1.sh Permission Meaning -rwxrwxr-- Symbol Meaning

• File d Directory r Read w Write x Execute

2. Directory Permissions

Check directory permissions:

ls -lrtd testing/

Output:

drwxr-xr-x 2 varghese varghese 4096 Mar 7 12:16 testing/

Explanation:

d -> directory r -> read w -> write x -> execute (enter directory)

If x permission exists, users can enter the directory.

Restrict Other Users chmod 774 testing/

Check permission:

ls -lrtd testing/

Output:

drwxrwxr-- 2 varghese varghese 4096 Mar 7 12:16 testing/ Folder Permission Read & Execute chmod 775 testing/

Output:

drwxrwxr-x 2 varghese varghese 4096 Mar 7 12:16 testing/

Meaning:

Owner → Read, Write, Execute

Group → Read, Write, Execute

Others → Read, Execute

Full Permission chmod 777 testing/

Output:

drwxrwxrwx 2 varghese varghese 4096 Mar 7 12:16 testing/

Meaning: Everyone has Full Access

3. Change Ownership

Change owner from varghese → tiju

sudo chown tiju:tiju testing

Check:

ls -lrtd testing/

Output:

drwxrwxrwx 2 tiju tiju 4096 Mar 7 12:16 testing/ Package Management Package Formats Format Description .deb Debian package .rpm RedHat Package Manager Install Package Using dpkg sudo dpkg -i package.deb apt Package Manager

Similar to Play Store for Linux.

Install multiple packages:

sudo apt install docker.io ansible curl wget List Installed Packages sudo dpkg -l

Example Output:

ii adduser 3.118ubuntu5 ii adwaita-icon-theme 41.0-1ubuntu1

ii means package is installed

Search Package

Example: Search Docker

sudo apt-cache search docker Find Installed Package Using grep

Example:

sudo dpkg -l | grep python

Output:

ii libpython3-stdlib ii libpython3.10 Apache Installation Example

Install Apache:

sudo apt install apache2

Check installed packages:

sudo dpkg -l | grep apache2

Output:

ii apache2 ii apache2-bin

ii → Installed package

Remove Package Remove Package Only sudo apt remove apache2 Purge Package

Remove package + config + documentation

sudo apt purge apache2

Check remaining packages:

sudo dpkg -l | grep apache2

Example remaining packages:

apache2-bin apache2-data apache2-utils

Remove all related packages:

sudo apt purge apache2*

Now check again:

sudo dpkg -l | grep apache2

Output:

(no output)

Apache completely removed.

Process Management Check Running Processes ps -ef

Example:

UID PID PPID C STIME TTY TIME CMD

More info:

man ps Process Management Example

Create script:

script.sh

Example content:

sleep 120

Run script:

sh script.sh Check Running Script ps -ef | grep -i script.sh

Output:

varghese 36384 115 0 13:42 pts/0 00:00:00 sh script.sh

PID of script: 36384

Kill Process sudo kill -9 36384

This will forcefully terminate the process.

Linux File Permision

varghese@DESKTOP-OODIU93:~/temp$ ls -lrt
total 8
-rw-r--r-- 1 varghese varghese  6 Mar  3 12:15 tiju
-rw-r--r-- 1 varghese varghese 17 Mar  3 12:36 script1.sh

varghese@DESKTOP-OODIU93:~/temp$ ./script1.sh
-bash: ./script1.sh: Permission denied

varghese@DESKTOP-OODIU93:~/temp$ ls -lrt script1.sh
-rw-r--r-- 1 varghese varghese 17 Mar  3 12:36 script1.sh

varghese@DESKTOP-OODIU93:~/temp$ chmod u=rwx script1.sh

varghese@DESKTOP-OODIU93:~/temp$ ls -lrt script1.sh
-rwxr--r-- 1 varghese varghese 17 Mar  3 12:36 script1.sh

varghese@DESKTOP-OODIU93:~/temp$ ./script1.sh
Tue Mar  3 13:02:41 EST 2026

varghese@DESKTOP-OODIU93:~/temp$

Granting Permission to Other Users

The chmod command can be used to modify file permissions.
Here we grant read, write, and execute permissions to other users.

Command

chmod o=rwx script1.sh

| Section | Meaning                 |
| ------- | ----------------------- |
| `rwx`   | Owner permissions       |
| `r--`   | Group permissions       |
| `rwx`   | Other users permissions |



# Absolute Path vs Relative Path

## Absolute Path
- Example: `ls /var/log/`
- Starts with `/` (root directory).
- It specifies the complete path from the root (`/`) to the target directory or file.
- It works from anywhere in the system.

## Relative Path
- Example: `ls var/log`
- Does NOT start with `/`.
- It specifies the path relative to your current working directory.
- It works only if the path exists from your current location.




Basic Linux Navigation Commands

This document explains some basic Linux terminal navigation commands.

1️⃣ Check Current Directory
pwd

Description:
Displays the current working directory.

Example Output:

/ home/varghese
2️⃣ List Files Inside a Directory Without Entering It
ls busapp

Description:
Lists all files and folders inside the busapp directory without navigating into it.

3️⃣ Change Directory
cd busapp

Description:
Moves into the busapp directory.

4️⃣ Move Up Two Directories
cd ../../

Description:
Moves up two levels in the directory structure.

Example:

/ home/varghese/busapp → / home
5️⃣ Go Back to Previous Directory
cd -

Description:
Returns to the previous directory you were in.

Example:

/ home → / home/varghese/busapp

cd - allows you to quickly switch back to your last working directory.


Go to Home Directory
cd ~

Description:
The ~ symbol represents the home directory of the current user.

Example:

varghese@DESKTOP-OODIU93:~/busapp$ cd ~
varghese@DESKTOP-OODIU93:~$ pwd
/home/varghese

This shows that you are now inside the home directory:
/home/varghese

2️⃣ List Files and Directories in Long Format
ls -l

Description:
Lists files and directories in the current location in long format.

Example Output:

total 36
drwxr-xr-x 6 varghese varghese 4096 Jan 13 11:40 Bash-Commands
drwxr-xr-x 2 varghese varghese 4096 Aug 22  2025 bash_varghese
drwxr-xr-x 3 varghese varghese 4096 Feb 21 18:30 busapp
drwxr-xr-x 3 varghese varghese 4096 Feb 19 11:52 busapp_Git_Demo_old
-rw-r--r-- 1 varghese varghese   14 Aug 26  2025 copy_tiju.txt
drwxr-xr-x 2 varghese varghese 4096 Dec 21  2024 from-windows
-rw-r--r-- 1 varghese varghese   79 Oct 22  2024 pg_hba.conf
drwx------ 3 varghese varghese 4096 Aug  2  2024 snap
drwxr-xr-x 4 varghese varghese 4096 Jan 10  2025 varghese
What ls -l Shows:

File type and permissions

Number of links

Owner name

Group name

File size

Last modified date

File or directory name

3️⃣ Listing a Specific Folder
ls -l varghese
Command Breakdown:

ls → Command (list directory contents)

-l → Option (long listing format)

varghese → Argument (the folder name to list)