EC
138
BashINFOCommonSignalHIGH confidence

User-defined signal 1 (SIGUSR1)

Production Risk

Without a handler, SIGUSR1 kills the process; always trap it in long-running services.

What this means

Exit code 138 (128+10) indicates the process received SIGUSR1. This signal has no predefined meaning — applications define their own handler for it. The default action (when no handler is set) is to terminate the process.

Why it happens
  1. 1Another process sent kill -USR1 PID
  2. 2A process manager uses SIGUSR1 for a specific action (e.g., log rotation in some daemons)
How to reproduce

Sending SIGUSR1 to a process with no handler.

trigger — this will error
trigger — this will error
#!/bin/bash
sleep 100 &
PID=$!
kill -USR1 $PID
wait $PID
echo "Exit: $?"

expected output

Exit: 138

Fix

Trap SIGUSR1 for custom application actions

WHEN Writing daemons or long-running scripts

Trap SIGUSR1 for custom application actions
#!/bin/bash
rotate_logs() {
  mv /var/log/myapp.log /var/log/myapp.log.1
  echo "Logs rotated at $(date)" > /var/log/myapp.log
}
trap rotate_logs USR1

echo "Running, PID $. Send USR1 to rotate logs."
while true; do
  sleep 1
done

Why this works

Trapping USR1/USR2 lets you implement operational controls (log rotation, status dump, reload) without stopping the service.

Sources
Official documentation ↗

GNU Bash Manual — Signals

Content generated with AI assistance and reviewed for accuracy. Found an error? hello@errcodes.dev

← All Bash errors