SIGPIPE Signal Explained (Signal 13)

SIGPIPE (signal 13) is sent when a process writes to a pipe or socket whose reader has closed, for example when head exits before the producer finishes.

What it does

Default action: Terminate. It can be caught with a signal handler.

Typically sent by: the kernel on writing to a closed pipe/socket. List all signals with kill -l.

Signal number and delivery

Practical examples

Send it from the shell

kill -13 <PID>
kill -SIGPIPE <PID>
pkill -13 nginx

Handle it in a script

trap 'echo got SIGPIPE; cleanup; exit' SIGPIPE
while true; do sleep 1; done

Handle it in code

import signal, sys
def handler(sig, frame):
    print('received', sig)
    sys.exit(0)
signal.signal(signal.SIGPIPE, handler)

Common mistakes

• Using kill -9 before trying SIGTERM.
• Forgetting to find the right PID (ps aux | grep, pgrep).
• Not handling signals in long-running services.

Key takeaways

• SIGPIPE is signal 13.
• Default: Terminate.
• Use kill -l to list all signals.

FAQ

Why does yes | head stop?

head exits, the next write by yes triggers SIGPIPE and ends it.

How do I list all signals?

Run kill -l.