These commands are useful for diagnosing runtime issues, checking system state, and validating connectivity.

System and Process Commands

Command	Purpose	Example
ps	List running processes	ps aux \| grep nginx
top	Interactive process and resource view	top
htop	Improved interactive process view	htop
kill	Send signal to process	kill -TERM 1234
df	Disk usage by filesystem	df -h
du	File and directory size usage	du -sh ./artifacts
free	Memory usage	free -h
uname	Kernel and OS info	uname -a

Network and Remote Access Commands

Command	Purpose	Example
ip	Interface and route information	ip addr show
ss	Socket/listening port inspection	ss -ltnp
ping	Basic connectivity test	ping -c 4 8.8.8.8
curl	HTTP/API requests	curl -I https://example.com
dig	DNS lookup and troubleshooting	dig example.com
ssh	Secure remote shell	ssh user@host
scp	Secure copy over SSH	scp file.txt user@host:/tmp/
rsync	Efficient sync over SSH	rsync -az ./data/ user@host:/data/

Troubleshooting Quick Checks

# Verify a service is listening on expected port
ss -ltnp | grep :443

# Check route and DNS before debugging app-level issues
ip route
dig internal-api.example.com

Safe Usage Tips

1. Prefer kill -TERM before kill -KILL.
2. Use ss instead of deprecated networking tools where possible.
3. Confirm destination paths before running rsync --delete.
4. Avoid running long-lived SSH commands without timeouts in automation.