Useful Linux Commands
This quick reference lists useful Linux commands for daily server administration, such as checking ports, finding large files, following logs and analyzing system load. The commands work on current distributions like Debian, Ubuntu, AlmaLinux and Rocky Linux.
Network & Processes
Check Port Usage
Which process is currently blocking a specific port?
lsof - Port Check
lsof -i tcp:80
Listening Connections
List all active programs waiting for incoming connections.
ss -tulpn
ss -tulpn
# Legacy alternative (package net-tools):
netstat -plunt
File Management
Determine Directory Sizes
Find the largest space consumers within a specific path.
du - Disk Usage
du -h --max-depth=1 /var/log
Locate Large Files
Search the entire system for files larger than 100 MB.
find - Large Files
find / -type f -size +100M
Live Log Monitoring
Output new log entries to the screen in real-time.
tail -f / journalctl -f
# systemd journal (all current distributions)
journalctl -f
# Classic log file (Ubuntu; AlmaLinux/Rocky: /var/log/messages)
tail -f /var/log/syslog
System Analysis
Disk Write Load (I/O)
Which service is causing the highest load on your storage? (Install iotop via your package manager if needed.)
iotop - I/O Monitor
iotop -o
Resource Overview (htop)
Interactive overview of CPU, RAM, and all running processes.
htop
htop
Productivity
Search Command History
Quickly find a command you used previously.
history search
history | grep "ssh"
Copy Files via SSH
Securely transfer files or directories between servers.
scp transfer
scp -r /local/path user@remote-ip:/destination/path
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