Monitor, control, and manage running processes on Linux using ps, top, kill, and systemd.

View Running Processes

# Snapshot of all processes
ps aux

# Show as tree
ps auxf

# Find a specific process
ps aux | grep nginx

# Interactive process monitor
top
htop   # install with: sudo apt install htop

Send Signals to Processes

# Kill by PID (graceful SIGTERM)
kill 1234

# Force kill (SIGKILL - no cleanup)
kill -9 1234

# Kill by name (all matching)
pkill nginx

# Kill all instances of a program
killall -9 python3

# Reload a process (SIGHUP)
kill -HUP 1234

Background Jobs

# Run in background
./long-script.sh &

# List background jobs
jobs

# Bring job to foreground
fg %1

# Send running process to background
Ctrl+Z  # pause the process
bg %1   # resume it in background

# Run immune to terminal close
nohup ./script.sh > output.log 2>&1 &

Manage Services with systemd

# Start / stop / restart
sudo systemctl start nginx
sudo systemctl stop nginx
sudo systemctl restart nginx

# Enable at boot
sudo systemctl enable nginx
sudo systemctl disable nginx

# Check status
sudo systemctl status nginx

# View service logs
sudo journalctl -u nginx -f --since "1 hour ago"

Process Priority (nice)

# Start process with low priority (nice -20 = highest, 19 = lowest)
nice -n 10 ./backup.sh

# Change priority of running process
sudo renice -n 5 -p 1234

# View current priorities in top: press 'r' to renice
top

Check Resource Usage

# Memory and CPU by process
ps aux --sort=-%mem | head -10
ps aux --sort=-%cpu | head -10

# Open file handles per process
ls -l /proc/1234/fd | wc -l
lsof -p 1234

# Check which process owns a port
sudo ss -tulpn | grep :80