Linux and Bash command-line interfaces form the backbone of modern cloud infrastructure, DevOps pipelines, and developer environments. Mastering terminal navigation, process management, file permissions, network utilities, and shell scripting enables system administrators and developers to operate Linux servers efficiently.
Key Takeaways
- Use `chmod` and `chown` to manage Linux file permissions and user access rights.
- Combine CLI tools via pipes (`|`) to stream data across grep, awk, sort, and uniq pipelines.
- Monitor real-time processes using `ps aux`, `htop`, and manage background jobs with `bg` and `fg`.
- Configure automated system tasks using `crontab -e` and establish secure remote connections via SSH.
How do you navigate the filesystem and manipulate files in Linux?
Filesystem navigation uses path operators (cd, pwd, ls), while file operations create, copy, move, and remove files and directories.
File & Directory Navigation
| Command | Action |
|---|---|
ls -la | List all files including hidden dotfiles with permissions & sizes |
cd /var/www | Change directory to /var/www |
cd .. | Move up one parent directory level |
cd ~ | Return to current user’s home directory |
cd - | Switch back to previously active working directory |
pwd | Print absolute working directory path |
mkdir -p path/to/dir | Create directory structure along with parent folders |
cp file.txt copy.txt | Copy a file |
cp -r dir/ copy_dir/ | Copy a directory recursively |
mv old.txt new.txt | Rename or move a file |
rm file.txt | Remove a file |
rm -r dir/ | Remove a directory recursively |
rm -rf dir/ | Force remove directory and contents without prompts |
ln -s target_file link_name | Create a symbolic link |
Reading & Inspecting File Contents
| Command | Action |
|---|---|
cat file.txt | Print entire file content to stdout |
less file.txt | Paginated interactive file viewer (press q to exit) |
head -n 20 file.txt | Display first 20 lines of a file |
tail -n 20 file.txt | Display last 20 lines of a file |
tail -f /var/log/syslog | Follow live stream updates to log files |
wc -l file.txt | Count total line count in a file |
wc -w file.txt | Count total word count in a file |
How do you search files and text using grep and find?
grep searches for text patterns inside files, while find locates files across directory trees based on name, size, or modification date.
Grep Text Searching
| Command | Action |
|---|---|
grep "pattern" file.txt | Search for exact pattern in a file |
grep -r "pattern" ./src | Search recursively across all files in directory |
grep -i "pattern" file.txt | Perform case-insensitive pattern match |
grep -n "pattern" file.txt | Display line numbers alongside matching text |
grep -v "pattern" file.txt | Invert match (display lines that do NOT match) |
grep -l "pattern" dir/* | List filenames containing pattern matches |
grep -C 3 "error" app.log | Display 3 lines of context before and after match |
Find File Searching
| Command | Action |
|---|---|
find . -name "*.js" | Find files matching name pattern |
find . -type f -name "*.log" | Find regular files only |
find . -type d -name "node_modules" | Find directories by name |
find . -mtime -7 | Find files modified within the last 7 days |
find . -size +10M | Find files larger than 10MB |
find . -name "*.tmp" -delete | Find and delete matching temporary files |
How do Linux file permissions and user access rights work?
Linux uses permission modes (read, write, execute) assigned to owner, group, and others to protect system files.
Permission Management
| Command | Action |
|---|---|
ls -l | Display detailed permissions, owner, and group |
chmod 755 script.sh | Set rwxr-xr-x permissions (Owner: read/write/exec, Group/Others: read/exec) |
chmod +x script.sh | Make file executable |
chmod -R 755 /var/www | Set permissions recursively across directory tree |
chown user file.txt | Change file owner |
chown user:group file.txt | Change file owner and group |
chown -R user:group dir/ | Change owner and group recursively |
sudo command | Execute command with superuser (root) privileges |
Permission Mode Numeric Breakdown
| Numeric Mode | Permission Scope | Symbol |
|---|---|---|
7 | Read + Write + Execute | rwx |
6 | Read + Write | rw- |
5 | Read + Execute | r-x |
4 | Read Only | r-- |
0 | No Permissions | --- |
How do you inspect processes, memory, disk usage, and network ports?
System administration requires monitoring CPU/RAM consumption, process lifecycles, disk space, and open network sockets.
Process Control & Resource Monitoring
| Command | Action |
|---|---|
ps aux | List all running system processes |
ps aux | grep node | Search for running process IDs by name |
top / htop | Interactive real-time process and system resource monitor |
kill PID | Terminate process gracefully (SIGTERM) |
kill -9 PID | Force terminate process immediately (SIGKILL) |
killall node | Kill all running processes named node |
df -h | Display disk space usage in human-readable units |
du -sh dir/ | Display total size of a directory |
free -h | Display total, used, and available system RAM memory |
Networking & SSH Utilities
| Command | Action |
|---|---|
ip a | Display network interfaces and IP addresses |
ss -tulnp | List active listening TCP/UDP network ports and process IDs |
ping host | Verify ICMP network reachability to remote host |
curl -I https://example.com | Fetch HTTP response status and headers |
ssh user@host | Open secure shell connection to remote server |
scp local.txt user@host:/remote/path/ | Copy file to remote server over SSH |
rsync -avz src/ user@host:/dest/ | Efficiently sync directories over SSH |
How do you manage archives, pipes, shell variables, and cron jobs?
Shell automation relies on standard input/output redirection (>, |), environment variables (export), and scheduled cron jobs.
Archives & Pipes
| Symbol / Command | Action |
|---|---|
tar -czf archive.tar.gz dir/ | Create gzipped tar archive |
tar -xzf archive.tar.gz | Extract gzipped tar archive |
cmd1 | cmd2 | Pipe output of cmd1 as input to cmd2 |
> file.txt | Redirect stdout to file (overwrite existing content) |
>> file.txt | Redirect stdout to file (append to existing content) |
2>&1 | Redirect stderr to stdout stream |
/dev/null | Discard output stream completely |
Shell Keyboard Shortcuts & Environment
| Shortcut / Command | Action |
|---|---|
Ctrl+C | Interrupt and kill currently executing process |
Ctrl+Z | Suspend running process to background |
Ctrl+L | Clear terminal screen |
Ctrl+R | Reverse search command history |
export VAR=value | Set an environment variable available to child subshells |
source ~/.bashrc | Reload active shell environment configuration |
Cron Scheduled Tasks (crontab -e)
bash
# Format: minute hour day-of-month month day-of-week command
# Run script every minute
* * * * * /path/to/script.sh
# Run script every day at midnight (00:00)
0 0 * * * /path/to/backup.sh
# Run script every Monday at 9:00 AM
0 9 * * 1 /path/to/weekly-report.sh
# Run script every 15 minutes
*/15 * * * * /path/to/health-check.shWriting Executable Bash Scripts (script.sh)
bash
#!/bin/bash
set -e # Exit immediately if any command returns non-zero error
set -u # Treat unset variables as errors
NAME="Developer"
echo "Processing deployment for $NAME..."
# Conditionals
if [ -f "config.json" ]; then
echo "Configuration file found."
else
echo "Configuration file missing!"
exit 1
fi
# Command substitution
TODAY=$(date +%Y-%m-%d)
echo "Deployment date: $TODAY"Frequently Asked Questions
What is the difference between > and >> in Bash?
> redirects command output to a file, completely overwriting any existing contents. >> appends command output to the end of the target file without overwriting existing data.
How do I make a Bash script executable?
Run chmod +x script.sh to add execute permissions, then execute it in your terminal using ./script.sh.
What to Read Next
- cURL Command-Line Cheat Sheet — Master HTTP requests and API testing.
- Vim Cheat Sheet: Modes & Navigation — Edit server files efficiently over SSH.
- Docker Cheat Sheet: Container Management — Run containerized Linux apps.
