📘 UNIX Commands - Study & Download

📄 Basic UNIX Commands

ln (Link)

ln origfile linkedfile: Hard Link – same inode, changes reflect in both files.

ln -s origfile linkedfile: Soft Link – can link across file systems, different inodes.

find

find path -name 'pattern': Search by name.

-type [f|d|l]: Search by file type.

-perm mode: Search by permission (e.g., 666 or 400).

-inum number: Search by inode.

-samefile file: Find all hard links.

-links +2: Files with link count > 2.

-user user: Files owned by user.

-size +x: Size-based search.

-mtime/-ctime/-atime [+/-n]: Time-based search (modified/created/accessed).

-follow: Follow symlinks.

-exec: Execute command (e.g., -exec rm {} \;).

-ok: Like -exec but with prompt.

-print: Print matches.

-ls: Detailed file list.

Logical Ops: -a (AND), -o (OR), ! (NOT).

ls

-a: Show hidden files.

-F: Mark file types.

-R: Recursive list.

-d: List dir names, not contents.

-l: Long format.

-n: Show UID/GID.

-t: Sort by modified time.

-ltr: Sort by time, oldest first.

-u: Sort by last access.

-i: Show inode number.

chmod

Grants file rights (r=4, w=2, x=1).

chmod 756 file: User=all, Group=rw, Others=rx.

-R: Recursive.

umask

Default perms: 666 (files), 777 (dirs).

umask 022 → Files=644, Dirs=755.

cp

-p: Preserve attributes.

cp -p src dest

chown

chown user file

-R: Recursive.

chgrp

chgrp group file

-R: Recursive.

-f: Force.

-h: Change symlink, not target.

touch

Create dummy file.

-m: Update modified time.

-a: Update access time.

echo

echo *: List current dir.

echo \*: Print *.

Escape: \n, \t, \c, \g (bell).

Wildcards

[a-z], [!x-z]: Pattern match.

Escape Characters

\n: New line

\t: Tab

\c: Suppress newline

\007 or \g: Bell

more

View file page-by-page.

/search: Search within file.

wc

-l: Lines

-w: Words

-c: Characters

pr

Prepare files for printing.

-l n: Set page length.

echo $$

Show current shell PID.

cmp

Compare files, show first diff.

-l: Byte by byte.

diff

Show differences to sync two files.

comm

Compare 2 sorted files.

-1: Suppress column 1.

-2: Suppress column 2.

-3: Suppress column 3.

head

head -n 10 file: Show top 10 lines.

tail

tail -n 10 file: Show last 10 lines.

tail -f file: Follow file changes.

tail +100 file: From line 100.

cut

-c: Character positions.

-d and -f: Delimited fields.

Example: cut -d: -f2-4 file

paste

Merge lines of files.

-d: Set delimiter.

sort

Sort file lines.

-r: Reverse.

-n: Numeric.

-k: Sort by column.

uniq

Remove duplicates.

-c: Count occurrences.

tr

Translate or delete.

tr 'a-z' 'A-Z' < file: Uppercase.

-d, -s: Delete, squeeze.

tee

Write output to file and stdout.

command | tee file

xargs

Convert input to arguments.

Example: find . -name '*.txt' | xargs wc -l

🧠 Advanced UNIX Commands

Below is a detailed and practical list of advanced Unix/Linux commands commonly used in critical production support environments, such as during release & deployment, remote access, file transfers, container operations, and cloud infrastructure tasks. Each command includes:

✅ Purpose

💡 Why it's used in production

🔧 Syntax & example

🔐 1. Remote Server Access & Management

✅ ssh – Secure Shell (Remote Login)
Purpose: Securely log into a remote Linux/Unix server.

Why in production: Daily use for accessing prod servers for troubleshooting, log checks, hotfixes.

Syntax:

ssh user@hostname_or_ip

Example:

ssh [email protected]
🔒 Use ~/.ssh/config for easier access with aliases.

📦 2. File Transfer Between Servers

✅ scp – Secure 
Purpose:  files securely between local and remote servers.

Why in production: Moving builds, logs, configs, database dumps during deployment or troubleshooting.

Syntax:

scp source_file user@remote_host:/target/path/

Example:

scp app.tar.gz [email protected]:/opt/releases/

🛠️ 3. Deployment and Build Utilities

✅ rsync – Efficient File Sync
Purpose: Incrementally sync files/directories across servers.

Why in production: Faster and safer than scp for deployment of large projects.

Syntax:

rsync -avz /local/dir/ user@remote:/remote/dir/

Example:

rsync -avz ./build/ [email protected]:/var/www/html/

🧰 4. Docker Operations (Containerized Deployments)

✅ docker ps, docker exec, docker logs, docker cp
Purpose: Manage Docker containers on prod/staging servers.

Why in production: Common for microservices-based apps.

Examples:

List running containers:

docker ps
Check logs for a container:

docker logs container_id
Enter a container’s shell (e.g., to debug):

docker exec -it container_id /bin/
 a file into a container:

docker cp config.yml container_id:/app/config/

☁️ 5. Cloud Operations (AWS CLI + Unix)

✅ aws s3 cp, aws ec2 describe-instances, aws logs tail
Purpose: Automate cloud-based file handling, instance management.

Why in production: S3 for backups/artifacts, EC2 for server automation, CloudWatch for logs.

Examples:

 to S3:

aws s3 cp logs.tar.gz s3://myprod-logs/ --region us-east-1
List running EC2 instances:

aws ec2 describe-instances --query "Reservations[*].Instances[*].[InstanceId,State.Name,Tags]" --output table
Stream CloudWatch logs:

aws logs tail /aws/lambda/myFunction --follow

🧮 6. Process and Resource Management

✅ top, htop, ps, kill
Purpose: Check CPU, memory, and terminate rogue processes.

Why in production: Monitor performance, troubleshoot high load, kill stuck processes.

Examples:

Check running processes:

ps aux | grep java
Kill a process:

kill -9 PID
Real-time monitoring:

top
# or more user-friendly:
htop

📁 7. Log Management

✅ tail, grep, awk, less, zcat
Purpose: Analyze logs in real time or retrospectively.

Why in production: Debugging critical issues like downtime, errors, etc.

Examples:

Tail logs live:

tail -f /var/log/nginx/error.log
Search errors:

grep "ERROR" /var/log/app.log
Extract field with awk:


awk '{print $5}' /var/log/app.log
View compressed logs:

zcat app.log.gz | grep timeout

🧪 8. Network & Connectivity

✅ netstat, ss, telnet, curl, ping, dig
Purpose: Verify network connectivity, check open ports.

Why in production: Diagnose latency, DNS issues, port access.

Examples:

Check open ports:

netstat -tuln
Ping a service:

ping google.com
Test HTTP endpoint:

curl -I https://yourapp.com/health
Check DNS resolution:

dig api.yourdomain.com

🧾 9. Scheduled Jobs

✅ crontab, at, systemctl
Purpose: Automate tasks (e.g., log rotation, backups).

Why in production: Automate recurring deployments, log archival, or checks.

Examples:

 crontab:

crontab -e
List current jobs:

crontab -l
Schedule one-time job (after 10 mins):


echo " /scripts/restart.sh" | at now + 10 minutes

📋 10. Backup & Archival

✅ tar, gzip, find
Purpose: Backup files and clean up old logs/artifacts.

Why in production: Storage management, retention compliance.

Examples:

Create backup:

tar -czvf backup_$(date +%F).tar.gz /var/www/html/

Delete logs older than 15 days:

find /var/log/myapp/ -name "*.log" -mtime +15 -exec rm {} \;

✨ Pro Tip: Combine Tools in One-liners

tail -f app.log | grep "Exception"

ssh user@prod-server 'docker logs myapp_container | tail -n 50'

find /logs/ -type f -name "*.log" -mtime +7 | xargs tar -czf old_logs.tar.gz

📥 Downloadable Study Materials: