Bash Process Management - ps, kill, top, bg, fg, jobs, nohup

Process Management in Bash

Understanding how to manage processes is critical for system administration and development. Bash provides tools for listing, monitoring, signaling, and controlling processes.

Viewing Processes with ps

The ps command shows information about running processes:

ps aux                          # all processes with details
ps aux | grep nginx             # find specific process
ps aux --sort=-%mem | head -10  # top 10 by memory usage
ps -ef --forest                 # process tree
ps -u www-data                  # processes for specific user

Killing Processes

The kill command sends signals to processes:

kill PID                  # SIGTERM (graceful shutdown, default)
kill -9 PID               # SIGKILL (force kill, cannot be caught)
kill -1 PID               # SIGHUP (reload configuration)
killall node              # kill all processes by name
pkill -f "python app.py"  # kill by command pattern

Monitoring with top and htop

top provides a real-time view of system resource usage:

top                   # interactive process viewer
top -bn 1 | head -20  # one snapshot for scripting
htop                  # enhanced version (if installed)

Background Jobs

Bash supports running processes in the background:

# Start in background
long_task &

# Suspend and background
# Press Ctrl+Z, then:
bg

# List background jobs
jobs

# Bring to foreground
fg %1

Keeping Processes Running

nohup prevents a process from being terminated when the terminal closes:

nohup ./server.sh > output.log 2>&1 &
disown                          # remove from shell's job table

Waiting for Processes

# Wait for all background jobs
wait

# Wait for specific PID
wait $PID

# Run commands in parallel and wait
task1 &
task2 &
task3 &
wait
echo "All tasks completed"

Process Substitution for Monitoring

# Watch a command repeatedly
watch -n 2 'ps aux | grep node'

# Monitor specific process
while kill -0 $PID 2>/dev/null; do
  echo "Process $PID still running..."
  sleep 5
done
echo "Process $PID has exited"