Dev

2025/git/01_Git_and_Github_Basics/solution.md

@@ -0,0 +1,26 @@
+Task 1: Fork and Clone the Repository
+git clone <https://github.com/apurva-kri/90DaysOfDevOps.git>
+cd 2025/git/01_Git_and_Github_Basics
+mkdir week-4-challenge
+cd week-4-challenge
+git init
+vim info.txt
+git add info.txt
+git commit -m "Initial commit: Add info.txt with introductory content"
+Task 3: Configure Remote URL with PAT and Push/Pull
+git remote set-url origin https://@github.com/apurva-kri/90DaysOfDevOps.git
+git push -u origin main
+git pull origin main
+Task 4: Explore Your Commit History
+git log
+Task 5: Advanced Branching and Switching
+git branch feature-update
+git switch feature-update
+git add info.txt
+git commit -m "Feature update: Enhance info.txt with additional details"
+git push origin feature-update
+
+Branching strategies are essential in collaborative development because they help teams work together efficiently and safely. By isolating features and bug fixes in separate branches, developers can work without affecting the stability of the main codebase. This separation also enables parallel development, allowing multiple team members to work on different tasks simultaneously without interfering with each other’s progress.
+
+Well-defined branching practices help reduce merge conflicts by keeping changes organized and focused within their own branches. Finally, they make code reviews more effective, as reviewers can easily understand the purpose of a branch, evaluate changes in isolation, and ensure quality before merging into the main branch.
+

2025/networking/Solution/Task1.md

@@ -0,0 +1 @@
+this is my submission for week one challenge

2025/networking/Solution/task2.md

@@ -0,0 +1,2 @@
+1 comment
+

2026/day-02/task-02/linux-architecture-notes.md

@@ -0,0 +1,57 @@
+# Day 02 – Linux Architecture, Processes, and systemd
+# Core Components of Linux
+
+## Kernel
+
+- Core of the OS; talks directly to hardware
+- Manages CPU, memory, disk, devices
+- Handles process scheduling and system calls
+
+## User Space
+
+- Where users and applications run
+- Includes shell (bash), utilities, libraries
+- Programs request resources from the kernel
+
+## Init / systemd (PID 1)
+
+- First process started by the kernel
+- Initializes the system after boot
+- Starts and manages background services
+
+# How Processes Are Created & Managed
+## Process Creation
+
+- fork() → Creates a copy of the parent process
+- exec() → Replaces process memory with a new program
+- Each process gets a unique PID
+
+## Process States (Important for Troubleshooting)
+
+- Running (R) → Actively using CPU
+- Sleeping (S) → Waiting for event/input (most common state)
+- Stopped (T) → Paused (e.g., via kill -STOP)
+- Zombie (Z) → Finished execution but parent hasn’t collected status
+- Idle → Kernel process doing nothing
+- Uninterruptible Sleep (D) → Waiting on I/O (disk/network), cannot be interrupted
+
+The kernel scheduler manages CPU time and priorities to ensure multitasking works efficiently.
+
+## What systemd does and why it matters
+# what it does:
+- Starts services at boot(SSh, netwroking, docker, etc)
+- Manages and monitor services
+- Restart failed services automatically
+- Handles logging(journald)
+- Control targets(run levels like multi-user, graphical)
+# Why it matters
+- Faster boot with parallel startup
+- Centralized service management
+- Better reliability and monitoring
+- Essential for Devops & server administration
+## 5 Linux commands I'd use daily
+- ps-aux -View running processes
+- top/htop - Monitor CPU & Memory usage
+- systemctl - Manages Services like start, stop, restart, status, enable, disable etc
+- journalctl - check logs
+- kill - stop or signal a process

2026/day-03/task-03/linux-commands-cheatsheet.md

@@ -0,0 +1,25 @@
+## 🐧Linux Command Cheat Sheet
+# 1. Process Management
+- ps - Display currently running processes
+- ps aux - show all processes with detailed info
+- top - Real-time system process monitoring
+- htop - interractive process viewer
+- kill <PID> - Terminate a process by PID
+- kill -9 <PID> - Force kill a process
+- pkill <name> - Kill process by name
+
+# 📁2. File System Commands
+- ls -l - List files with detailed permissions
+- ls -a - Show hidden files
+- cd <dir> - Change directory
+- pwd - show current directory 
+- rm -r <dir> - Remove directory recursively
+- cat <file> - Display file content
+- chmod 755 <file> - Change file permissions
+
+# 🌐3. Networking & Troubleshooting
+- ping <host> - Check network connectivity
+- curl <url> - Fetch data from URL(API testing)
+- wget <url> - Downloads file from internet
+- dig <domain> - DNS lookup for domain
+- ip addr - Show IP address configuration

2026/day-04/task-04/linux-practice.md

@@ -0,0 +1,37 @@
+## Day 04 – Linux Practice: Processes and Services
+# Service Management (systemd)
+- systemctl status ssh - Check the current status of the SSH service (running, stopped, failed, logs)
+- systemctl status sshd -Check the status of the SSH daemon (used in some distributions like CentOS/RHEL)
+- systemctl is-enabled ssh -Verify whether the SSH service is enabled to start automatically at boot
+- systemctl cat ssh -Display the complete unit file configuration of the SSH service
+- systemctl list-units -List all currently active units loaded in memory by systemd
+- systemctl list-units --type=service -List only active service-type units (filters out other unit types like mount, socket, etc.)
+- systemctl list-units --failed -Display all failed units to quickly identify services that crashed or failed to start
+# Process Monitoring (ps)
+- ps -Display processes running in the current terminal session
+- ps aux -Show all running processes with detailed information (user, CPU, memory, etc.)
+- ps aux | head -Show the first 10 processes from the detailed process list
+- ps aux | head -n 5 -Display only the first 5 processes from the full process list
+- ps aux | tail -n 5 -Display the last 5 processes from the full process list
+- ps aux | grep ssh -Filter and show only processes related to SSH
+- ps aux | grep ssh | grep -v grep -Show SSH-related processes while excluding the grep command itself
+- ps aux --sort=-%cpu -Diplay all processes sorted by highest CPU usage first
+- ps aux --sort=-%mem -Display all processes sorted by highest memory usage first
+- ps aux --sort=-%cpu | head -n 5 -Show the top 5 processes consuming the most CPU
+- ps aux --sort=-%mem | head -n 5 -Show the top 5 processes consuming the most memory
+- ps aux --sort=-%cpu | grep ssh | head -n 5 -Display the top 5 SSH-related processes sorted by CPU usage
+- ps -C sshd -Show processes that match the exact command name sshd
+- ps -C sshd --sort=-%cpu | head -n 5 -Display the top 5 sshd processes sorted by CPU usage
+# Log Inspection (tail, journalctl)
+- tail -n 5 file.txt -Display the last 5 lines of a file
+- tail -n 50 filename.log -Display the last 50 lines of a log file
+- tail -n 50 filename.log -Display the last 50 lines of a log file (used for reviewing recent activity)
+- tail -f filename.log -Monitor a file in real time as new lines are added
+- tail -n 5 -f filename.log -Show the last 5 lines and continue monitoring the file live
+- tail -n 5 /var/log/auth.log -Display the last 5 SSH authentication log entries (Ubuntu/Debian systems)
+- tail -f /var/log/auth.log -Monitor SSH authentication logs in real time
+- journalctl -u ssh -Display all logs related to the SSH service (systemd-based systems)
+- journalctl -u ssh -n 5 -Show the last 5 log entries for the SSH service
+- journalctl -u ssh -f -Monitor SSH service logs live using systemd journal
+
+

2026/day-05/task-05/linux-troubleshooting-runbook.md

@@ -0,0 +1,110 @@
+# Day 05 – Linux Troubleshooting Drill: CPU, Memory, and Logs
+Target Service : SSH
+## Environment basics
+- `uname -a` -> Tell me everything about this system. uname is unix name and -a indicates all information.
+```
+Linux ip-172-31-44-23 6.14.0-1018-aws #18~24.04.1-Ubuntu SMP Mon Nov 24 19:46:27 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
+```
+- `lsb_release -a` -> Tell me the Linux distribution details
+```
+Distributor ID: Ubuntu
+Description:    Ubuntu 24.04.1 LTS
+Release:        24.04
+Codename:       noble
+```
+# Filesystem sanity
+- `mkdir /tmp/runbook-demo`
+- `cp /etc/hosts /tmp/runbook-demo/hosts-copy`
+- `ls -l /tmp/runbook-demo` - Filesystem writable. Copy successful. Permissions intact.
+```
+total 4
+-rw-r--r-- 1 ubuntu ubuntu 221 Feb  8 22:08 hosts-copy
+```
+# CPU / Memory
+- `ps -o pid,pcpu,comm -p 30607` -Process-level view
+```
+  PID %CPU COMMAND
+  30607  0.1 sshd
+  ```
+  - `free -h` -Memory overview
+  ```
+                total        used        free      shared  buff/cache   available
+  Mem:           914Mi       383Mi       129Mi       2.8Mi       569Mi       530Mi
+  Swap:             0B          0B          0B
+  ```
+# Disk / IO
+  - `df -h`
+  ```
+  Filesystem       Size  Used Avail Use% Mounted on
+  /dev/root        6.8G  2.9G  3.9G  42% /
+  tmpfs            458M     0  458M   0% /dev/shm
+  tmpfs            183M  928K  182M   1% /run
+  tmpfs            5.0M     0  5.0M   0% /run/lock
+  efivarfs         128K  3.8K  120K   4% /sys/firmware/efi/efivars
+  /dev/nvme0n1p16  881M  151M  669M  19% /boot
+  /dev/nvme0n1p15  105M  6.2M   99M   6% /boot/efi
+  tmpfs             92M   12K   92M   1% /run/user/1000
+  ```
+  - `du -sh /var/log` - log directory size
+  ```
+  178M    /var/log -Total visible log size ≈ 178 MB /Disk usage normal
+  ```
+  # Network 
+  -`ss -tlunp` - “Show me all TCP & UDP ports that are currently listening, with numeric IPs and the process name.”
+  - ss = socket statistics
+  - t  → TCP
+  - l  → Listening sockets only
+  - u  → UDP
+  - n  → Show numbers (don’t resolve names)
+  - p  → Show process using the port
+  ```
+  Netid     State      Recv-Q     Send-Q             Local Address:Port          Peer Address:Port     Process     
+  udp       UNCONN     0          0                      127.0.0.1:323                0.0.0.0:*
+  udp       UNCONN     0          0                     127.0.0.54:53                 0.0.0.0:*
+  ```
+  # ping - Can I reach this host over the network? It sends small network packets (ICMP Echo Requests) and waits for replies.
+  - `ping google.com`
+  ```
+  --- www.google.com ping statistics ---
+  5 packets transmitted, 5 received, 0% packet loss, time 4005ms
+  ```
+  # Logs 
+  - `journalctl -u ssh -n 2` -Modern Linux systems (like your Ubuntu 24.04) use systemd, and it stores service logs in a centralized logging system called the journal. This shows the last 2 log entries.
+  ```
+  Feb 08 22:33:53 ip-172-31-44-23 sshd[30508]: Accepted publickey for ubuntu from 157.49.9.58 port 51173 ssh2: RSA>
+  Feb 08 22:33:53 ip-172-31-44-23 sshd[30508]: pam_unix(sshd:session): session opened for user ubuntu(uid=1000) by>
+  ```
+  - `tail -n 50 /var/log/auth.log | grep ssh`- Take only the last 5 lines of the log file.
+  - `grep ssh /var/log/auth.log | tail -n 5` - Find all sshd logs first, then show the last 5 of those.
+  ```
+  2026-02-08T21:24:51.274485+00:00 ip-172-31-44-23 sshd[30011]: Accepted publickey for ubuntu from 157.49.28.21 port 64832 ssh2: RSA SHA256:HBvpRqJvL+gVCvTfZNpc5T6VWAfFukD48PFoOIj5s08
+  2026-02-08T21:24:51.276370+00:00 ip-172-31-44-23 sshd[30011]: pam_unix(sshd:session): session opened for user ubuntu(uid=1000) by ubuntu(uid=0)
+  ```
+  # If This Worsens (Next Steps)
+  If SSH becomes unstable (high CPU, refusing connections, hanging sessions):
+  - `sudo systemctl restart ssh`
+  If issue persists:
+  - `sudo systemctl status ssh`
+  - `journalctl -u ssh -n 100`
+  If repeated failures:
+  Check port conflicts (ss -tlunp)
+  Confirm firewall rules (sudo ufw status)
+  Validate no disk full issues (df -h)
+  # Increase Log Verbosity (Temporary) -If logs are unclear or insufficient:
+  - edit ssh config - `sudo nano /etc/ssh/sshd_config`
+  - Change or add: `LogLevel VERBOSE`
+  - Then restart SSH: -`sudo systemctl restart ssh`
+  - This provides: Detailed authentication logs ,Connection debugging info, More granular failure reasons
+  # Deep Process & System Analysis -If CPU/memory spikes or SSH freezes:
+  - Check live process behavior: `top`
+  - If disk-related symptoms appear: - `df -h`
+
+
+
+
+
+
+
+
+
+

2026/day-06/task-06/file-io-practice.md

@@ -0,0 +1,50 @@
+
+# Practice Basic File Read/Write
+
+## 1. Creating file And Writing text to a file
+`touch notes.txt`
+
+`echo "Learning basic linux file operations." > notes.txt`
+
+## 2. Appending new lines
+
+`echo "Using touch to create files" >> notes.txt` { append new line to a file }
+
+`echo "Using echo to write content" >> notes.txt`
+
+`echo "understanding overwite with >" >> notes.txt`
+
+`echo "Appending new lines using >>" | tee -a notes.txt` { -a = append and **tee** use to write text on file along with display}
+
+## 3. Reading Full And Part of File
+`cat notes.txt`
+
+**Output Snippet:**
+```
+Learning basic Linux file operations
+Using touch to create files
+Using echo to write content
+Understanding overwrite with >
+Appending new lines using >>
+Reading files using cat
+Viewing partial content with head
+Checking last lines with tail
+Using tee to write and display
+```
+
+`head -n 3 notes.txt` {head -n 3 = print 3 lines from top}
+
+**Output Snippet:**
+```
+Learning basic Linux file operations
+Using touch to create files
+Using echo to write content
+```
+`tail -n 3 notes.txt` {tail -n 3 = print last three lines}
+
+**Output Snippet:**
+```
+Viewing partial content with head
+Checking last lines with tail
+Using tee to write and display
+```