What is the difference between SIGTERM and SIGKILL?

SIGTERM (15) is a polite termination request that a process can catch to clean up before exiting, and is what kill sends by default. SIGKILL (9) forces immediate termination and cannot be caught, blocked or ignored, so the process gets no chance to clean up.

Which signals cannot be caught?

Only two: SIGKILL (9) and SIGSTOP (19). They cannot be caught, blocked or ignored, which guarantees the kernel can always terminate or suspend a process regardless of its handlers.

How do exit codes relate to signals?

When a process is killed by a signal, the shell reports an exit code of 128 plus the signal number. So a process killed by SIGKILL (9) exits with 137, and one interrupted by SIGINT (2) exits with 130.

Are signal numbers the same on every system?

The low signals (SIGKILL 9, SIGTERM 15, SIGINT 2) are consistent, but some numbers differ across architectures and operating systems. Always refer to a signal by name in portable code rather than by its raw number.

Is anything I search uploaded?

No. The signal table and the search run entirely in your browser, so nothing you type is sent anywhere.

Unix Signals Reference

This is a searchable reference for Unix and Linux signals — the asynchronous notifications the kernel and processes use to communicate events like interrupts, faults and termination requests. Each entry gives the number, the symbolic name, the default disposition if no handler is installed, and whether the signal can be caught.

How it works

A signal is delivered to a process by number; the C library maps names like SIGTERM to those numbers. If the process has no handler, the kernel applies the default action: Terminate (end the process), Core dump (end and write a core file), Stop (suspend), Continue (resume a stopped process), or Ignore. A process can install a handler for most signals, but SIGKILL (9) and SIGSTOP (19) are special — they cannot be caught, blocked or ignored, so the kernel can always force termination or suspension. Search by number, by name (the SIG prefix is optional), by action or by keyword.

Common signals

The ones you send most: SIGTERM (15, polite kill), SIGKILL (9, forced kill), SIGHUP (1, hang-up — many daemons reload config), SIGINT (2, Ctrl+C), SIGTSTP (20, Ctrl+Z), SIGCONT (18, resume), and the user-defined SIGUSR1/SIGUSR2 (10/12). Fault signals you usually see in crashes: SIGSEGV (11, bad memory), SIGBUS (7), SIGFPE (8), SIGABRT (6).

Example

Sending signals from the shell — note the exit code that results:

$ kill -TERM 4321     # ask process 4321 to shut down (catchable)
$ kill -9 4321        # force kill if it ignores SIGTERM
$ echo $?             # a process killed by signal 9 exits 137 (128 + 9)

Always try SIGTERM first so the process can clean up; reach for SIGKILL only when it refuses to stop. Everything in this tool runs in your browser; nothing is uploaded.

Unix Signals Reference

Email me this result

How it works

Common signals

Example