Home›Linux in 5 Days›Day 4
Day 4 of 5
⏱ ~60 minutes
Linux in 5 Days — Day 4

Processes and System Monitoring

View running processes, manage them, control services with systemctl, and monitor disk and memory.

Viewing Processes

Process commands
# List all processes
ps aux
# ps aux | grep nginx   ← find a specific process

# Interactive process viewer
top         # built-in, Ctrl+C to exit
htop        # prettier version (install if needed)

# htop keys:
# F9 = kill process
# F6 = sort by column
# / = search
Signals and Kill
# Get PID from ps aux output
kill 1234              # send SIGTERM (graceful)
kill -9 1234           # send SIGKILL (force kill)
killall nginx          # kill all processes named nginx
pkill -f 'python app'  # kill by command pattern

# Background jobs
sleep 60 &             # run in background
jobs                   # list background jobs
fg %1                  # bring job 1 to foreground
bg %1                  # continue job 1 in background
systemctl: Managing Services
# Start/stop/restart
sudo systemctl start nginx
sudo systemctl stop nginx
sudo systemctl restart nginx
sudo systemctl reload nginx  # reload config without restart

# Enable/disable on boot
sudo systemctl enable nginx
sudo systemctl disable nginx

# Check status
systemctl status nginx
journalctl -u nginx -f    # follow nginx logs
Disk and Memory
df -h                  # disk usage by filesystem
du -sh ./mydir/        # size of a directory
du -sh * | sort -h     # sizes of all items, sorted

free -h                # memory usage
cat /proc/meminfo      # detailed memory info

# Find large files
du -ah . | sort -rh | head -20
📝 Day 4 Exercise
Monitor Your System
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Day 4 Summary

  • ps aux | grep name finds a process. kill PID stops it. kill -9 forces it.
  • systemctl start/stop/restart/enable/status service — the full service management toolkit.
  • journalctl -u service -f follows a service's logs in real-time.
  • df -h shows disk usage. du -sh dir/ shows directory size. free -h shows memory.
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Day 3: Permissions and Users
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Day 5: Shell Scripting
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