process-cleanup（进程清理）

Process Cleanup

Detect and reap zombie processes using /bin/ps.

Background

A zombie (state Z) is a process that has exited but whose parent hasn't called wait() to collect its exit status. Zombies consume no CPU or memory, but they hold a PID slot and can accumulate. You can't kill a zombie — it's already dead. The only remedies are:

1. Signal the parent with SIGCHLD so it reaps the child
2. Kill the parent so init/launchd adopts and reaps the orphan

Important: use ps for process state queries

Always use ps (BSD) for process state queries. If ps is aliased, use /bin/ps to bypass it.

# List zombies
/bin/ps ax -o pid,state,ppid,user,command | awk '$2 ~ /Z/'

# List all processes with state
/bin/ps ax -o pid,state,ppid,etime,args

Usage

Run the helper script to scan for zombies:

# Detect only (default) — list zombie processes
bash scripts/kill-zombies.sh

# Reap zombies — send SIGCHLD to parent processes
bash scripts/kill-zombies.sh --kill

Safety

• Default mode is detect-only — no processes are signaled
• With --kill, the script sends SIGCHLD to parent processes (non-destructive nudge to reap)
• If a parent ignores SIGCHLD, the script reports the parent PID — confirm with the user before killing it
• Never kill PID 1 (init/launchd)