Process Management

Working Code

Example 1: Checking running processes

ps

Example output:

  PID TTY           TIME CMD
 1234 ttys001    0:00.05 -zsh
 5678 ttys001    0:00.01 ps

Column meanings:

• PID: Process ID (unique number for each process)
• TTY: Terminal connection info
• TIME: CPU time used
• CMD: Running command

For more detail:

ps aux

Example output:

USER       PID  %CPU %MEM      VSZ    RSS   TT  STAT STARTED      TIME COMMAND
dale      1234   0.0  0.1  408952   2056 s001  S   10:00am   0:00.05 -zsh
dale      5678   0.0  0.0  408400    896 s001  R+  10:05am   0:00.01 ps aux

Additional columns:

• %CPU: CPU usage
• %MEM: Memory usage
• STAT: Process state (S=sleeping, R=running, Z=zombie)

Example 2: Finding a specific process

ps aux | grep node

Output:

dale      3456   0.2  1.5 123456  30000 s001  S   09:00am   0:02.10 node server.js

Example 3: Finding which process is using a port

# Find the process using port 3000
lsof -i :3000

Output:

COMMAND   PID USER   FD   TYPE   DEVICE SIZE/OFF NODE NAME
node     3456 dale   23u  IPv6   0x...     0t0  TCP *:3000 (LISTEN)

Check the PID and terminate it:

kill 3456

Try It Yourself

Background Execution

# Append & to run in the background
sleep 30 &

Output:

[1] 7890

[1] is the job number, 7890 is the PID.

# List background jobs
jobs

Output:

[1]  + running    sleep 30

# Bring a background job to the foreground
fg %1

# Pause a foreground job (Ctrl+Z)
# Then resume it in the background
bg %1

Terminating Processes

# Request graceful termination (SIGTERM, default)
kill 7890

# Force immediate termination (SIGKILL, when unresponsive)
kill -9 7890

# Terminate by job number
kill %1

Checking Disk Usage

# Overall disk usage (human-readable)
df -h

Output:

Filesystem     Size   Used  Avail Capacity  Mounted on
/dev/disk1s1  500G   120G   375G    25%    /
/dev/disk1s2  500G   120G   375G    25%    /System/Volumes/Data

# Size of a specific directory
du -sh ~/Documents

Output:

2.1G    /Users/dale/Documents

# Size by subdirectory (top 5)
du -sh ~/Documents/* | sort -rh | head -5

Output:

1.5G    /Users/dale/Documents/Videos
342M    /Users/dale/Documents/Projects
 89M    /Users/dale/Documents/Archive
 12M    /Users/dale/Documents/Docs
4.0K    /Users/dale/Documents/notes.txt

"Why?" — When You Need Process Management

| Scenario | Solution | | --------------------------------------------- | ------------------------------------------------------ | ---------------------------------- | | Dev server unresponsive | ps aux | grep node-> find PID ->kill PID | | Port 3000 already in use | lsof -i :3000 -> find PID -> kill PID | | Need to do other work during a build/download | Run with command & | | Running out of disk space | df -h for overview, du -sh * to find large folders |

kill Signals Reference

| Signal | Number | Meaning | When to Use | | --------- | ------ | --------------------- | ---------------------- | | SIGTERM | 15 | Graceful termination | Default, try first | | SIGKILL | 9 | Forced immediate kill | When unresponsive | | SIGINT | 2 | Interrupt (Ctrl+C) | Foreground termination | | SIGHUP | 1 | Restart | Reload configuration |

Always try kill (SIGTERM) first. Only use kill -9 if the process doesn't respond. SIGKILL gives the process no chance to clean up.

Common Mistakes

Mistake 1: Using kill -9 first

# Bad habit
kill -9 1234   # process can't clean up temp files, sockets, etc.

# Good habit
kill 1234      # try graceful termination first
# if no response, then use -9
kill -9 1234

Mistake 2: Running kill without checking the PID

# Dangerous: might terminate the wrong process
kill 1

# Safe: check first
ps aux | grep node
# ... confirm the PID ...
kill 1234

Mistake 3: Losing background jobs

Closing the terminal also terminates background jobs. To keep a process running after the terminal closes:

# nohup: keep running after terminal closes
nohup python server.py &

# Output is saved to nohup.out
tail -f nohup.out

Deep Dive

top

brew install htop
htop