Create linux-architecture-notes.md

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

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+pwd  --> give present working directory
+
+cd --> change directory
+
+ls --> list the items
+
+mkdir --> make directory
+
+touch --> creates a file
+
+cp  --> used to copy form one directory to another
+            copy source  destination
+
+       if u wanna copy one directory into another
+            cp -r src-directory-name dest-directory-name
+
+mv ----> used to move the files
+
+mv  source destination
+
+rm  --> to remove
+    rv  source destination
+ip addr --> to check ip address and other details
+
+Hostname --> will give Hostname
+
+Hostname -I --> will give ip address
+
+ping --> to check pertiuclar website working or not
+
+free --> to check how much ram is free
+
+df --> disk file how much available
+
+cat   filename --> display the content of the file

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

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+Process Management
+
+ps aux # List all running processes
+ps aux | grep nginx # Search for a process by name 
+kill -9 <PID> # Kill a process by PID 
+top # Monitor processes in real time 
+htop # Better interactive process viewer (if installed)
+
+
+
+File System
+df -h # Show disk usage in human-readable format
+du -sh /var/log # Show size of a directory
+ls -l # List files with details
+chown user:group file # Change file ownership
+chmod 644 file # Change file permissions
+
+Networking Troubleshooting
+
+ip addr show # Show IP addresses of interfaces
+ping google.com # Test connectivity
+traceroute google.com # Trace route to a host
+netstat -tulnp # Show open ports (older tool)
+ss -tulnp # Show open ports (modern replacement)
+dig example.com # Check DNS resolution
+curl -I https://example.com  # Send HTTP request and show headers

2026/day-04/linux-practice.md

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+Task 1 – Check Running Processes
+ps -a
+Shows active processes attached to terminals (except session leaders).
+
+PID → Process ID
+
+TTY → Terminal associated
+TIME → CPU time consumed
+CMD → Command executed
+
+Output:
+    root@TWS-BATCH-10-SERVER:~# ps -a
+    PID TTY          TIME CMD
+    2143 pts/0    00:00:00 ps
+
+
+top
+Real‑time monitoring tool for processes and system performance.
+
+Displays:
+    CPU usage
+    Memory usage
+    Load average (1, 5, 15 minutes)
+    Process list with PID, USER, priority, memory, CPU %, etc.
+
+    root@TWS-BATCH-10-SERVER:~# top
+top - 14:59:30 up 1 min,  1 user,  load average: 0.56, 0.24, 0.09
+Tasks: 192 total,   1 running, 191 sleeping,   0 stopped,   0 zombie
+%Cpu(s):  0.2 us,  0.3 sy,  0.0 ni, 99.5 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
+MiB Mem :   3915.9 total,   2604.1 free,    969.4 used,    564.5 buff/cache
+MiB Swap:      0.0 total,      0.0 free,      0.0 used.   2946.5 avail Mem
+
+
+Task 2 – Inspect One Systemd Service
+Command: systemctl list-units --type=service
+Output: Shows all loaded services and their states (running, exited, failed).
+
+jenkins.service   loaded active running Jenkins Continuous Integration Server
+docker.service    loaded active running Docker Application Container Engine
+
+systemctl status jenkins.service
+Output:
+● jenkins.service - Jenkins Continuous Integration Server
+     Loaded: loaded (/usr/lib/systemd/system/jenkins.service; enabled)
+     Active: active (running) since Tue 2026-01-27 14:58:38 UTC; 8min ago
+   Main PID: 756 (java)
+      Tasks: 44
+     Memory: 644.7M
+        CPU: 30.905s
+     CGroup: /system.slice/jenkins.service
+             └─756 /usr/bin/java -jar /usr/share/java/jenkins.war
+
+Task 3 – Capture a Small Troubleshooting Flow
+command: systemctl status jenkins.service
+output: Confirms if Jenkins is active or failed.
+
+
+journalctl -u jenkins.service -n 50
+
+Shows last 50 log entries for Jenkins.
+Useful for spotting errors (e.g., port conflicts, permission issues).
+
+ls -ld /var/lib/jenkins
+drwxr-xr-x 16 jenkins jenkins 4096 Jan 27 14:58 /var/lib/jenkins
+
+
+
+
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+

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

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+root@TWS-BATCH-10-SERVER:~# systemctl list-units --type=service 
+  UNIT                                           LOAD   ACTIVE SUB     DESCRIPTION                                     >
+  apparmor.service                               loaded active exited  Load AppArmor profiles
+  apport.service                                 loaded active exited  automatic crash report generation
+  blk-availability.service                       loaded active exited  Availability of block devices
+  cloud-config.service                           loaded active exited  Cloud-init: Config Stage
+  cloud-final.service                            loaded active exited  Cloud-init: Final Stage
+  cloud-init-local.service                       loaded active exited  Cloud-init: Local Stage (pre-network)
+  cloud-init.service                             loaded active exited  Cloud-init: Network Stage
+  console-setup.service                          loaded active exited  Set console font and keymap
+  containerd.service                             loaded active running containerd container runtime
+  cron.service                                   loaded active running Regular background program processing daemon
+  dbus.service                                   loaded active running D-Bus System Message Bus
+  docker.service                                 loaded active running Docker Application Container Engine
+  finalrd.service                                loaded active exited  Create final runtime dir for shutdown pivot root
+  [email protected]                             loaded active running Getty on tty1
+  jenkins.service                                loaded active running Jenkins Continuous Integration Server
+  keyboard-setup.service                         loaded active exited  Set the console keyboard layout
+  kmod-static-nodes.service                      loaded active exited  Create List of Static Device Nodes
+  lvm2-monitor.service                           loaded active exited  Monitoring of LVM2 mirrors, snapshots etc. using>
+  ModemManager.service                           loaded active running Modem Manager
+  multipathd.service                             loaded active running Device-Mapper Multipath Device Controller
+  plymouth-quit-wait.service                     loaded active exited  Hold until boot process finishes up
+  plymouth-quit.service                          loaded active exited  Terminate Plymouth Boot Screen
+  plymouth-read-write.service                    loaded active exited  Tell Plymouth To Write Out Runtime Data
+  polkit.service                                 loaded active running Authorization Manager
+  rsyslog.service                                loaded active running System Logging Service
+  setvtrgb.service                               loaded active exited  Set console scheme
+  snapd.apparmor.service                         loaded active exited  Load AppArmor profiles managed internally by sna>
+  snapd.seeded.service                           loaded active exited  Wait until snapd is fully seeded
+
+checking the status of jenkins
+
+root@TWS-BATCH-10-SERVER:~# systemctl status jenkins
+● jenkins.service - Jenkins Continuous Integration Server
+     Loaded: loaded (/usr/lib/systemd/system/jenkins.service; enabled; preset: enabled)
+     Active: active (running) since Wed 2026-01-28 14:46:52 UTC; 24min ago
+   Main PID: 750 (java)
+      Tasks: 44 (limit: 4653)
+     Memory: 488.0M (peak: 488.8M)
+        CPU: 1min 40.541s
+     CGroup: /system.slice/jenkins.service
+             └─750 /usr/bin/java -Djava.awt.headless=true -jar /usr/share/java/jenkins.war --webroot=/var/cache/jenkins>
+
+Jan 28 14:46:50 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:50.186+0000 [id=38]        INFO        jenkins.InitR>
+Jan 28 14:46:50 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:50.496+0000 [id=37]        INFO        h.p.b.g.Globa>
+Jan 28 14:46:51 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:51.932+0000 [id=37]        INFO        jenkins.InitR>
+Jan 28 14:46:51 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:51.933+0000 [id=36]        INFO        jenkins.InitR>
+Jan 28 14:46:52 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:52.008+0000 [id=39]        INFO        jenkins.InitR>
+Jan 28 14:46:52 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:52.027+0000 [id=38]        INFO        jenkins.InitR>
+Jan 28 14:46:52 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:52.088+0000 [id=39]        INFO        jenkins.InitR>
+Jan 28 14:46:52 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:52.171+0000 [id=30]        INFO        o.j.p.g.j.Job>
+Jan 28 14:46:52 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:52.174+0000 [id=30]        INFO        hudson.lifecy>
+Jan 28 14:46:52 TWS-BATCH-10-SERVER systemd[1]: Started jenkins.service - Jenkins Continuous Integration Server.
+lines 1-20/20 (END)
+
+
+finding the PID of jenkins
+
+root@TWS-BATCH-10-SERVER:~# ps aux | grep jenkins
+jenkins      750  6.0  9.7 3724660 391264 ?      Ssl  14:46   1:41 /usr/bin/java -Djava.awt.headless=true -jar /usr/share/java/jenkins.war --webroot=/var/cache/jenkins/war --httpPort=8080
+root        1800  0.0  0.0   7076  2048 pts/0    S+   15:14   0:00 grep --color=auto jenkins
+root@TWS-BATCH-10-SERVER:~#
+
+
+checking PID, memory cpu command
+root@TWS-BATCH-10-SERVER:~# ps -o pid,comm,%mem,%cpu -p 750
+    PID COMMAND         %CPU %MEM
+    750 java             4.7  9.7
+
+df -h --> command is used to check how much each file system consuming the space
+
+root@TWS-BATCH-10-SERVER:~# df -h
+Filesystem      Size  Used Avail Use% Mounted on
+tmpfs           392M 1020K  391M   1% /run
+/dev/vda1        77G  5.8G   71G   8% /
+tmpfs           2.0G     0  2.0G   0% /dev/shm
+tmpfs           5.0M     0  5.0M   0% /run/lock
+/dev/vda16      881M  117M  703M  15% /boot
+/dev/vda15      105M  6.2M   99M   6% /boot/efi
+tmpfs           392M   16K  392M   1% /run/user/0
+root@TWS-BATCH-10-SERVER:~# df -h
+Filesystem      Size  Used Avail Use% Mounted on
+tmpfs           392M 1020K  391M   1% /run
+/dev/vda1        77G  5.8G   71G   8% /
+tmpfs           2.0G     0  2.0G   0% /dev/shm
+tmpfs           5.0M     0  5.0M   0% /run/lock
+/dev/vda16      881M  117M  703M  15% /boot
+/dev/vda15      105M  6.2M   99M   6% /boot/efi
+tmpfs           392M   16K  392M   1% /run/user/0
+
+checking jenkins files memory consumption 
+root@TWS-BATCH-10-SERVER:~# du -sh /var/lib/jenkins
+399M    /var/lib/jenkins
+root@TWS-BATCH-10-SERVER:~# du -sh /var/lib/
+2.9G    /var/lib/
+root@TWS-BATCH-10-SERVER:~# du -sh /var
+3.2G    /var
+
+
+
+Network activity
+
+root@TWS-BATCH-10-SERVER:~# ss -tulpn | grep 8080
+tcp   LISTEN 0      50                 *:8080             *:*    users:(("java",pid=750,fd=9))
+root@TWS-BATCH-10-SERVER:~#
+
+checking the logs
+
+journalctl -u jenkins --since "1 hour ago"
+Jan 28 14:46:40 TWS-BATCH-10-SERVER systemd[1]: Starting jenkins.service - Jenkins Continuous Integration Server...
+Jan 28 14:46:42 TWS-BATCH-10-SERVER jenkins[750]: Running from: /usr/share/java/jenkins.war
+Jan 28 14:46:42 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:42.906+0000 [id=1]        INFO        winstone.Logge>
+Jan 28 14:46:43 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:43.094+0000 [id=1]        WARNING        o.e.j.ee9.n>
+Jan 28 14:46:43 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:43.231+0000 [id=1]        INFO        org.eclipse.je>
+Jan 28 14:46:44 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:44.157+0000 [id=1]        INFO        o.e.j.e.w.Stan>
+Jan 28 14:46:44 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:44.241+0000 [id=1]        INFO        o.e.j.s.Defaul>
+Jan 28 14:46:44 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:44.895+0000 [id=1]        INFO        hudson.WebAppM>
+Jan 28 14:46:45 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:45.118+0000 [id=1]        INFO        o.e.j.s.handle>
+Jan 28 14:46:45 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:45.144+0000 [id=1]        INFO        o.e.j.server.A>
+Jan 28 14:46:45 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:45.145+0000 [id=1]        INFO        org.eclipse.je>
+Jan 28 14:46:45 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:45.146+0000 [id=31]        INFO        winstone.Logg>
+Jan 28 14:46:45 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:45.383+0000 [id=30]        INFO        jenkins.model>
+Jan 28 14:46:45 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:45.595+0000 [id=37]        INFO        jenkins.InitR>
+Jan 28 14:46:45 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:45.866+0000 [id=38]        INFO        jenkins.InitR>
+Jan 28 14:46:50 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:50.137+0000 [id=37]        INFO        jenkins.InitR>
+Jan 28 14:46:50 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:50.179+0000 [id=37]        INFO        jenkins.InitR>
+Jan 28 14:46:50 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:50.186+0000 [id=38]        INFO        jenkins.InitR>
+Jan 28 14:46:50 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:50.496+0000 [id=37]        INFO        h.p.b.g.Globa>
+Jan 28 14:46:51 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:51.932+0000 [id=37]        INFO        jenkins.InitR>
+Jan 28 14:46:51 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:51.933+0000 [id=36]        INFO        jenkins.InitR>
+Jan 28 14:46:52 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:52.008+0000 [id=39]        INFO        jenkins.InitR>
+Jan 28 14:46:52 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:52.027+0000 [id=38]        INFO        jenkins.InitR>
+Jan 28 14:46:52 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:52.088+0000 [id=39]        INFO        jenkins.InitR>
+Jan 28 14:46:52 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:52.171+0000 [id=30]        INFO        o.j.p.g.j.Job>
+Jan 28 14:46:52 TWS-BATCH-10-SERVER jenkins[750]: 2026-01-28 14:46:52.174+0000 [id=30]        INFO        hudson.lifecy>
+Jan 28 14:46:52 TWS-BATCH-10-SERVER systemd[1]: Started jenkins.service - Jenkins Continuous Integration Server.
+lines 1-27/27 (END)
+