Day 8 - Logs and Text Processing in Linux

On Day 8, I explored the powerful world of Linux log files and text processing commands. These are essential for DevOps, sysadmin tasks, debugging, and automation.

🔍 What I Learned Today

🔹 Working with Logs

• Viewed and followed log output:

      tail -f /var/log/messages
      tail -f /var/log/yum.log
      less +F yum.log
  

• Navigated configuration files:

    grep -i firewall anaconda-ks.cfg
    grep -R SELINUX /etc/*
    vim /etc/selinux/config
  

  Text Exploration Tools

• Viewers: cat, less, more, head, tail

• Search & Filter:

grep -i firewall anaconda-ks.cfg
grep -R selinux /etc/

• Field Extraction:

    cut -d: -f1 /etc/passwd   # usernames
    cut -d: -f3 /etc/passwd   # UIDs
    awk -F':' '{print $1}' /etc/passwd
  

  Text Manipulation with sed

  • Edited files inline:

      sed -i 's/coronavirus/covid19/g' samplefile.txt
      sed -i 's/covid19/nothing/g' samplefile.txt
    

    Key Learnings

    • How to monitor live log output (tail -f)

    • Use cut, awk, and grep to extract structured text

    • Automate bulk text replacements with sed

    • Investigated system config files (/etc/passwd, anaconda-ks.cfg, SELinux configs)

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🧠 This knowledge will help in:

• Reading audit logs

• Debugging boot issues

• Managing users and services

• Automating file edits in pipelines