Every major cloud platform runs Linux. Docker containers run Linux. Kubernetes nodes run Linux. CI/CD pipelines run on Linux. If you are going to work in DevOps, you will spend a large part of your career working on Linux systems, often remotely via SSH. Being fluent in Linux is not optional -- it is the foundation everything else is built on.
When I first connected to an AWS EC2 instance via SSH and found myself at a bare terminal with no GUI, no mouse, no file browser, I felt lost. Within a few weeks of daily practice, that terminal became home. Now navigating, debugging, and configuring Linux systems is faster and more powerful than any GUI could be.
Essential Navigation Commands
pwd # Print working directory
ls # List files
ls -la # List all files with details and hidden files
ls -lh # Human-readable sizes (KB, MB, GB)
cd /home/ubuntu # Change directory (absolute path)
cd .. # Go up one directory
cd ~ # Go to home directory
cd - # Go back to previous directory
# Finding files
find /etc -name "*.conf" # Find conf files in /etc
find /var/log -mtime -7 # Files modified in last 7 days
find / -size +100M # Files larger than 100MB
locate nginx.conf # Fast find (uses database)
which python3 # Where is this command?
type docker # What kind of command is this?File Operations
mkdir -p /app/logs/2025 # Create nested directories
touch file.txt # Create empty file / update timestamp
cp file.txt backup.txt # Copy file
cp -r dir/ backup/ # Copy directory recursively
mv file.txt /tmp/ # Move file
mv old-name.txt new-name.txt # Rename file
rm file.txt # Delete file (permanent!)
rm -rf /tmp/old-dir/ # Delete directory recursively
# View file contents
cat file.txt # Print entire file
less file.txt # Scroll through file (q to quit)
head -20 file.txt # First 20 lines
tail -20 file.txt # Last 20 lines
tail -f /var/log/nginx/access.log # Follow live log outputFile Permissions
Linux permissions control who can read, write, and execute files. Every file has three permission sets: owner, group, and others.
ls -la
# -rw-r--r-- 1 suraj devs 1234 Jan 1 12:00 config.txt
# drwxr-xr-x 2 root root 4096 Jan 1 12:00 scripts/
# Permissions breakdown: rwxrwxrwx = owner group others
# r=4 w=2 x=1
# chmod: change permissions
chmod 755 script.sh # rwxr-xr-x -- owner full, others read+exec
chmod 644 config.txt # rw-r--r-- -- owner read+write, others read
chmod +x deploy.sh # Add execute permission to all
chmod -R 750 /app/ # Recursive: apply to all files in directory
# chown: change ownership
chown ubuntu:ubuntu /app
chown -R www-data:www-data /var/www/htmlProcess Management
ps aux # All running processes
ps aux | grep nginx # Find nginx process
top # Live process monitor
htop # Better live monitor (install: apt install htop)
# Kill processes
kill 1234 # Send SIGTERM (graceful)
kill -9 1234 # Send SIGKILL (force kill)
pkill nginx # Kill by name
killall python3 # Kill all processes with name
# Background processes
./long-script.sh & # Run in background
nohup ./script.sh & # Run immune to hangups (survives SSH disconnect)
jobs # List background jobs
fg 1 # Bring job 1 to foregroundText Processing Tools
# grep: search for patterns
grep "ERROR" /var/log/app.log
grep -i "error" log.txt # Case-insensitive
grep -r "password" /etc/ # Recursive search
grep -v "DEBUG" app.log # Show lines NOT matching
grep -c "ERROR" app.log # Count matching lines
grep -A 3 "FATAL" app.log # Show 3 lines AFTER match
# awk: process columns
awk '{print $1, $3}' file.txt # Print columns 1 and 3
awk -F: '{print $1}' /etc/passwd # Print usernames (: separator)
awk '$3 > 1000 {print $1}' /etc/passwd # UIDs above 1000
# sed: stream editor (find and replace)
sed 's/localhost/production.db/g' config.txt
sed -i 's/DEBUG/INFO/g' app.conf # Edit file in-placeFrequently Asked Questions
What Linux distribution should I learn for DevOps?
Ubuntu LTS (Long Term Support) for learning and development. Amazon Linux 2 or Ubuntu on AWS EC2 for production. Most concepts transfer between distributions. Ubuntu is the best choice to start because documentation and community support are excellent.
What is sudo and when do I use it?
sudo (superuser do) runs a command with root/administrator privileges. Use it when commands require elevated access: sudo apt install, sudo systemctl restart nginx. Avoid running everything as root -- use sudo only when necessary for security.
How do I view system logs in Linux?
journalctl -xe for systemd logs. tail -f /var/log/syslog for system log. tail -f /var/log/nginx/error.log for nginx. dmesg for kernel messages. journalctl -u nginx for a specific service.
What is the difference between ./ and /usr/bin/?
./ runs a file from the current directory. Commands like ls, grep are in /usr/bin/ and /usr/sbin/ which are in your PATH -- so you can run them from anywhere without ./ prefix. Run which nginx to find where any command lives.
How do I monitor disk usage in Linux?
df -h shows disk usage by filesystem (h for human readable). du -sh * shows size of each item in current directory. du -sh /var/log/* shows what is filling up /var/log. ncdu is an interactive disk usage viewer (install: apt install ncdu).
In Part 3, we cover Git and version control -- the foundation of all modern software development and DevOps workflows.
Daily Linux navigation
pwd # Print working directory
ls # List files
ls -la # List all files with details and hidden files
ls -lh # Human-readable sizes (KB, MB, GB)
cd /home/ubuntu # Change directory (absolute path)
cd .. # Go up one directory
cd ~ # Go to home directory
cd - # Go back to previous directory
# Finding files
find /etc -name "*.conf" # Find conf files in /etc
find /var/log -mtime -7 # Files modified in last 7 days
find / -size +100M # Files larger than 100MB
locate nginx.conf # Fast find (uses database)
which python3 # Where is this command?
type docker # What kind of command is this?File Operations
mkdir -p /app/logs/2025 # Create nested directories
touch file.txt # Create empty file / update timestamp
cp file.txt backup.txt # Copy file
cp -r dir/ backup/ # Copy directory recursively
mv file.txt /tmp/ # Move file
mv old-name.txt new-name.txt # Rename file
rm file.txt # Delete file (permanent!)
rm -rf /tmp/old-dir/ # Delete directory recursively
# View file contents
cat file.txt # Print entire file
less file.txt # Scroll through file (q to quit)
head -20 file.txt # First 20 lines
tail -20 file.txt # Last 20 lines
tail -f /var/log/nginx/access.log # Follow live log outputFile Permissions
Linux permissions control who can read, write, and execute files. Every file has three permission sets: owner, group, and others.
ls -la
# -rw-r--r-- 1 suraj devs 1234 Jan 1 12:00 config.txt
# drwxr-xr-x 2 root root 4096 Jan 1 12:00 scripts/
# Permissions breakdown: rwxrwxrwx = owner group others
# r=4 w=2 x=1
# chmod: change permissions
chmod 755 script.sh # rwxr-xr-x -- owner full, others read+exec
chmod 644 config.txt # rw-r--r-- -- owner read+write, others read
chmod +x deploy.sh # Add execute permission to all
chmod -R 750 /app/ # Recursive: apply to all files in directory
# chown: change ownership
chown ubuntu:ubuntu /app
chown -R www-data:www-data /var/www/htmlProcess Management
ps aux # All running processes
ps aux | grep nginx # Find nginx process
top # Live process monitor
htop # Better live monitor (install: apt install htop)
# Kill processes
kill 1234 # Send SIGTERM (graceful)
kill -9 1234 # Send SIGKILL (force kill)
pkill nginx # Kill by name
killall python3 # Kill all processes with name
# Background processes
./long-script.sh & # Run in background
nohup ./script.sh & # Run immune to hangups (survives SSH disconnect)
jobs # List background jobs
fg 1 # Bring job 1 to foregroundText Processing Tools
# grep: search for patterns
grep "ERROR" /var/log/app.log
grep -i "error" log.txt # Case-insensitive
grep -r "password" /etc/ # Recursive search
grep -v "DEBUG" app.log # Show lines NOT matching
grep -c "ERROR" app.log # Count matching lines
grep -A 3 "FATAL" app.log # Show 3 lines AFTER match
# awk: process columns
awk '{print $1, $3}' file.txt # Print columns 1 and 3
awk -F: '{print $1}' /etc/passwd # Print usernames (: separator)
awk '$3 > 1000 {print $1}' /etc/passwd # UIDs above 1000
# sed: stream editor (find and replace)
sed 's/localhost/production.db/g' config.txt
sed -i 's/DEBUG/INFO/g' app.conf # Edit file in-placeFrequently Asked Questions
What Linux distribution should I learn for DevOps?
Ubuntu LTS (Long Term Support) for learning and development. Amazon Linux 2 or Ubuntu on AWS EC2 for production. Most concepts transfer between distributions. Ubuntu is the best choice to start because documentation and community support are excellent.
What is sudo and when do I use it?
sudo (superuser do) runs a command with root/administrator privileges. Use it when commands require elevated access: sudo apt install, sudo systemctl restart nginx. Avoid running everything as root -- use sudo only when necessary for security.
How do I view system logs in Linux?
journalctl -xe for systemd logs. tail -f /var/log/syslog for system log. tail -f /var/log/nginx/error.log for nginx. dmesg for kernel messages. journalctl -u nginx for a specific service.
What is the difference between ./ and /usr/bin/?
./ runs a file from the current directory. Commands like ls, grep are in /usr/bin/ and /usr/sbin/ which are in your PATH -- so you can run them from anywhere without ./ prefix. Run which nginx to find where any command lives.
How do I monitor disk usage in Linux?
df -h shows disk usage by filesystem (h for human readable). du -sh * shows size of each item in current directory. du -sh /var/log/* shows what is filling up /var/log. ncdu is an interactive disk usage viewer (install: apt install ncdu).
In Part 3, we cover Git and version control -- the foundation of all modern software development and DevOps workflows.
" style="max-width:100%;height:auto;border-radius:12px;" loading="lazy" width="680"/>Key takeaways
- Git is the universal version control system. Master `add`, `commit`, `push`, `pull`, `branch`, `merge`, `rebase`, `log`, `diff`, `stash` — that's most of daily Git.
- Branching strategies: trunk-based for fast-moving teams, GitFlow for slower release cycles. Pick one consciously; don't drift into chaos.
- Rebase locally for clean history, merge when collaborating. Never rebase shared branches — you'll rewrite history under someone else's feet.
- `.gitignore`, semantic commit messages, signed commits — small habits that scale beautifully across years and teams.
