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About this tool
Explore Linux signals with default actions, catchability, matching exit codes and how they behave as PID 1 in containers.
This explorer documents all 31 standard Linux signals from the signal(7) man page — number, default action (terminate, core dump, ignore, stop or continue), whether the signal can be caught, and the 128+N exit code a shell reports when it kills a process. It is written for developers and SREs debugging killed processes, container shutdowns and CI failures, including PID 1 behaviour that makes docker stop hang on naive entrypoints.
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All 31 standard signals with default action, catchability and typical cause in one searchable table.
Every fatal signal shows its 128+N shell exit code, so 137 and SIGKILL are one lookup apart.
Covers OOM kills, seccomp SIGSYS deaths, zombie reaping and the Docker and Kubernetes stop sequences.
SIGTERM (signal 15) is a polite, catchable termination request — a process can trap it, finish work and exit cleanly. SIGKILL (signal 9) cannot be caught, blocked or ignored: the kernel terminates the process immediately with no cleanup. That is why docker stop sends SIGTERM first and only escalates to SIGKILL after the grace period (10 seconds by default, 30 in Kubernetes).
Exactly two: SIGKILL (9) and SIGSTOP (19). Every other signal can have a handler installed or be blocked. This is by design, so an administrator can always terminate or suspend a runaway process no matter what it does.
Because your process runs as PID 1, and the kernel only delivers a signal to PID 1 if the process installed a handler for it — an unhandled SIGTERM is silently discarded. Fix it by handling SIGTERM in your application, using an init shim like tini (docker run --init), or using the shell exec form so your binary, not a shell, is PID 1.
Ctrl+C sends SIGINT, signal 2, to the foreground process group. If the process dies from it, the shell reports exit code 130 — 128 plus the signal number. Ctrl+Z sends SIGTSTP (suspend) and Ctrl+\ sends SIGQUIT, which also dumps core.