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Processes, ports and jobs

Inspecting what runs, stopping it gracefully, checking which port is busy, and keeping work alive after logout.

What is running

ps aux | grep nginx
top                    # live overview, q to quit
htop                   # friendlier top (install if missing)
pgrep -l node

pstree -p | head       # parent/child relationships
Column in ps auxMeaning
USEROwner of the process
%CPU / %MEMResource usage
PIDProcess id — how you target it
STATState; useful when diagnosing zombies

Stopping processes

kill 1234          # SIGTERM - polite request to stop
kill -9 1234       # SIGKILL - cannot be caught, use last
pkill -f 'node app'
killall nginx
⚠️
Always try SIGTERM before -9. Killing outright skips cleanup, which can leave locks, partial writes, or orphaned children behind.

Ports and connections

ss -ltnp                 # listening TCP ports + process
lsof -i :3000            # who owns port 3000
ss -tuln

curl -I localhost:3000   # quick health check
curl -s -o /dev/null -w '%{http_code} %{time_total}s\n' https://example.com

'Address already in use' means something holds the port. Find it with lsof -i :PORT rather than blindly restarting.

Background jobs

long-task &        # run in background
Ctrl-Z             # suspend the foreground job
bg                 # resume it in the background
fg                 # bring it back to foreground
jobs               # list

nohup ./serve.sh > serve.log 2>&1 &   # survives logout
# or use tmux/screen for a real session

Background jobs started with & still belong to your shell; nohup ignores hangup signals. For long-lived work, tmux is more robust than either.

FAQ

Process will not die even after kill -9?
It may be a zombie waiting to be reaped by its parent, or blocked in uninterruptible I/O (often NFS). Check STAT in ps aux.
How do I see what a service logged?
With systemd: journalctl -u nginx -f. Otherwise check /var/log/.

SSH, packages and services Files and permissions

Last refreshed 2026-09-17.