💻 Top 100 Linux Commands for Middleware & DevOps Engineers ⚙️ (Includes SSH, SSH-Key & Telnet) | MiddlewareBox
💻 Linux is the backbone of every Middleware and DevOps ecosystem — running enterprise tools like WebSphere, JBoss, Jenkins, Docker, and Ansible .
⚙️ This post brings together 100+ essential Linux commands — covering file management, networking, SSH, cron jobs, and systemctl operations used daily by engineers.
🔐 Learn secure connectivity practices with SSH and SSH-Key management, plus essential testing using Telnet.
🚀 Ideal for Middleware Engineers, DevOps professionals, and System Administrators aiming to strengthen their Linux command-line mastery.
📁 1️⃣ File & Directory Management
🧩 Command
💡 Description
pwd Show current directory ls -lh List files in readable format ls -lrt Sort files by modification time cd /opt/app Change directory mkdir -p /data/logs/archive Create nested directories rm -rf /tmp/logs Remove directory recursively cp -rp /opt/config /backup/ Copy files with permissions mv old.log new.log Rename or move file cat file.txt Display file content du -sh /opt Show directory size df -h Display filesystem usage touch file.txt Create an empty file
🧾 2️⃣ Search & Text Processing
🔍 Command
💡 Description
grep "error" logfile.log Search keyword in file grep -i "critical" /var/log/syslog Case-insensitive search grep -r "Exception" /opt/app/ Recursive search awk '{print $1,$3}' logfile.log Print specific columns sort -u file.txt Sort and remove duplicates uniq -c file.txt Count unique lines wc -l file.txt Count number of lines head -n 10 file.txt Show first 10 lines tail -n 50 logfile.log Show last 50 lines tail -f jenkins.log Watch logs live sed -i 's/http:/https:/g' nginx.conf Replace text in file
⚙️ 3️⃣ Process & Performance Monitoring
⚙️ Command
💡 Description
top Real-time process viewer htop Interactive process viewer ps -ef | grep java Show running Java processes kill -9 <pid> Kill process by ID lsof -i :8080 Find process using a port vmstat 2 5 Show CPU/memory stats every 2s iostat -x 1 Disk performance summary free -m Memory usage (in MB) uptime System load average sar -u 2 3 CPU utilization snapshot journalctl -u nginx.service -f Follow logs for systemd service dmesg | tail -20 Check kernel/system logs
🌐 4️⃣ Network & Connectivity
🌍 Command
💡 Description
ping www.google.com Check connectivity curl -I https://middlewarebox.com Get HTTP headers wget https://example.com/file.zip Download file ip addr Display IP addresses ip route Show routing table ss -tulwn Show listening ports netstat -plant Display active connections nc -zv 10.0.0.5 22 Test port access traceroute 8.8.8.8 Trace route to host nslookup middlewarebox.com DNS lookup dig middlewarebox.com Detailed DNS query
🔑 5️⃣ SSH & Secure Connectivity Commands
🔑 Command
💡 Description
ssh user@hostname Connect to remote server ssh -i ~/.ssh/id_rsa user@10.0.0.10 Use specific private key ssh-copy-id user@server Copy SSH key for passwordless login ssh -v user@server Verbose SSH connection (debug) scp file.txt user@remote:/tmp/ Securely copy files between systems rsync -avz /opt/app/ user@server:/backup/ Sync files securely over SSH ssh-agent bash Start SSH authentication agent ssh-add ~/.ssh/id_rsa Add SSH private key to agent
🔐 6️⃣ SSH-Key Management (Essential for DevOps)
🔐 Command
💡 Description
ssh-keygen -t rsa -b 4096 -C "your_email@example.com" Generate a new SSH key pair ls ~/.ssh/ List existing SSH keys and configs cat ~/.ssh/id_rsa.pub View your public key ssh-copy-id user@server Copy public key for passwordless login ssh -i ~/.ssh/id_rsa user@server Connect using a private key chmod 700 ~/.ssh Secure SSH directory chmod 600 ~/.ssh/id_rsa & chmod 644 ~/.ssh/id_rsa.pub Set correct key permissions ssh -T git@github.com Test SSH auth with GitHub ssh-agent bash & ssh-add ~/.ssh/id_rsa Load key into SSH agent
💡 TIP:
SSH keys allow secure, passwordless access between servers —
commonly used in Jenkins, Ansible, and Git integrations for DevOps automation .
🌍 7️⃣ Telnet Commands (Essential)
🌍 Command
💡 Description
telnet hostname port Test basic TCP connectivity telnet 10.0.0.10 443 Check HTTPS port reachability telnet mail.server.com 25 Test SMTP mail server connection
⚙️ 8️⃣ User & Permission Management
👤 Command
💡 Description
whoami Show current user id Display user ID and groups adduser devops Create a new user passwd devops Set user password usermod -aG sudo devops Add user to sudo group groups devops Show user group memberships chmod +x deploy.sh Make script executable chown root:root /opt/app Change file ownership
📦 9️⃣ Compression & Archiving
📦 Command
💡 Description
tar -cvf backup.tar /data Create tar archive tar -xvf backup.tar Extract tar file gzip file.txt Compress file gunzip file.txt.gz Decompress file zip -r backup.zip /opt/app Create zip archive unzip backup.zip Extract zip archive
🛠️ 1️⃣0️⃣ System & Service Management
🛠️ Command
💡 Description
systemctl status firewalld Check firewalld service status systemctl start firewalld Start firewalld service systemctl stop firewalld Stop firewalld service systemctl enable firewalld Enable firewalld at boot systemctl disable firewalld Disable firewalld from starting at boot
📦 1️⃣1️⃣ Package Management
📦 Command
💡 Description
apt update Update package lists (Debian/Ubuntu) apt install <package> Install package (Debian/Ubuntu) yum update Update packages (RHEL/CentOS) yum install telnet / apt install telnet Install Telnet client on RHEL / Ubuntu
⏰ 1️⃣2️⃣ Cron & Scheduling (Small but essential)
⏰ Command
💡 Description
crontab -l List current user's cron jobs crontab -e Edit current user's cron jobs using the default editor sudo crontab -e -u username Edit another user's cron jobs (requires sudo) cat /etc/crontab View system-wide cron file
🧠 🔟 Productivity & Shortcuts
⚡ Command
💡 Description
history Show previous commands !! Re-run last command !sudo Run last command as sudo alias ll='ls -la' Create command alias unalias ll Remove alias ctrl + r Search command history clear Clear terminal screen
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