Process management is essential for system administration, debugging, and resource optimization. This chapter covers how to monitor, control, and prioritize running processes in Linux.
Contents
1. Viewing Processes (ps)
The ps command shows running processes.
Basic Usage
ps # Shows your current shell's processes
ps aux # Detailed list of ALL running processes
ps -ef | grep nginx # Find specific processKey Columns in ps aux
| Column | Meaning |
|---|---|
USER | Process owner |
PID | Process ID |
%CPU | CPU usage |
%MEM | Memory usage |
COMMAND | Running command |
2. Interactive Monitoring (top, htop)
top (Basic Process Viewer)
top
- Key Controls:
q→ QuitShift + M→ Sort by memoryShift + P→ Sort by CPUk→ Kill a process (enter PID)
htop (Enhanced Version)
htop offers detailed and interactive information about system resources and processes running. You can filter information as well.
htop
# Install with `sudo apt install htop` (if missing)- Colorful, scrollable, and mouse-friendly
- Easily kill processes (
F9) or sort (F6)
3. Killing Processes (kill, killall, xkill)
Graceful Termination
kill -15 PID # Politely ask to stop (SIGTERM)
killall nginx # Kill all processes named "nginx"Force Kill (Use Sparingly)
kill -9 PID # Brutal force kill (SIGKILL)
xkill # GUI mode: click a window to kill it4. Background Jobs (&, jobs, fg, bg)
Run a Command in Background
long_running_command & # Runs in backgroundManage Background Jobs
jobs # List background jobs
fg %1 # Bring job 1 to foreground
bg %2 # Resume job 2 in background
Ctrl + Z # Suspend current foreground job5. Process Priority (nice, renice)
Launch a Low-Priority Process
nice -n 19 cpu_intensive_task # Lowest priority (19)
nice -n -20 critical_task # Highest priority (-20)Change Priority of Running Process
renice -n 10 -p PID # Set priority to 10Priority Range
| Value | Effect |
|---|---|
-20 | Highest priority |
0 | Default |
19 | Lowest priority |
Practical Examples
Find and Kill a Frozen Process
ps aux | grep "bad_program" kill -9 [PID]Monitor CPU-Hungry Processes
top -o %CPU # Sort by CPU usageRun a Script in Background
./backup.sh & # Runs the script in the background
jobs # Lists all background jobs
fg # Bring to foreground
# To stop or kill it manually, first find its PID:
ps aux | grep backup.sh
# Note Process it Then kill it: lets say process id is 50011
kill <50011>Limit Resource Usage
nice -n 19 ./heavy_script.sh # Low prioritySummary Cheat Sheet
| Command | Description |
|---|---|
ps aux | List all processes |
top | Live process monitor |
kill -9 PID | Force kill |
command & | Run in background |
nice -n 5 cmd | Start with low priority |
renice -n 10 -p PID | Change priority |