Linux signals: numbers, names and default actions

updated 2026-10-20

tool: GNU coreutils
versions: Linux kernel
os: linux

On Linux (x86, ARM and most other architectures) the common signals are SIGHUP 1, SIGINT 2, SIGQUIT 3, SIGKILL 9, SIGTERM 15, SIGCHLD 17 and SIGSTOP 19. A process killed by signal n is reported by the shell with exit status 128 + n, so 137 means SIGKILL and 143 means SIGTERM.

Signal table (x86/ARM numbering)

From signal(7). Numbers differ on Alpha, SPARC, MIPS and PA-RISC.

No.	Signal	Default action	Meaning
1	SIGHUP	Term	Hangup on the controlling terminal; daemons often reload config
2	SIGINT	Term	Interrupt from keyboard (Ctrl+C)
3	SIGQUIT	Core	Quit from keyboard (Ctrl+\)
4	SIGILL	Core	Illegal instruction
5	SIGTRAP	Core	Trace/breakpoint trap
6	SIGABRT	Core	Abort signal from abort(3)
7	SIGBUS	Core	Bus error (bad memory access)
8	SIGFPE	Core	Erroneous arithmetic operation
9	SIGKILL	Term	Kill signal; cannot be caught or ignored
10	SIGUSR1	Term	User-defined signal 1
11	SIGSEGV	Core	Invalid memory reference
12	SIGUSR2	Term	User-defined signal 2
13	SIGPIPE	Term	Broken pipe: write to a pipe with no readers
14	SIGALRM	Term	Timer signal from alarm(2)
15	SIGTERM	Term	Termination signal (kill default)
17	SIGCHLD	Ign	Child stopped, terminated or continued
18	SIGCONT	Cont	Continue if stopped
19	SIGSTOP	Stop	Stop process; cannot be caught or ignored
20	SIGTSTP	Stop	Stop typed at terminal (Ctrl+Z)
21	SIGTTIN	Stop	Terminal input for background process
22	SIGTTOU	Stop	Terminal output for background process
23	SIGURG	Ign	Urgent condition on socket
24	SIGXCPU	Core	CPU time limit exceeded
25	SIGXFSZ	Core	File size limit exceeded
28	SIGWINCH	Ign	Window resize
31	SIGSYS	Core	Bad system call

Default actions: Term terminates, Core terminates with a core dump, Ign is ignored, Stop stops the process, Cont resumes it.

Send a signal

bash

kill -TERM 1234      # same as kill 1234
kill -9 1234         # SIGKILL: last resort, no cleanup
kill -HUP "$(cat /run/nginx.pid)"
kill -l              # list signal names on this system

Sources

codes · bashBash exit codes: 0, 1, 2, 126, 127, 128+n and 255What bash exit codes mean: 0 success, 1 general error, 2 misuse of builtins, 126 not executable, 127 not found, 128+n killed by signal n, and how to read $?.glossary · coreutilsWhat is a zombie process (defunct) in Linux?A zombie is a finished process whose parent has not read its exit status with wait(). It shows as Z or <defunct> in ps and goes away when the parent reaps it.codes · nodejsNode.js exit codes: 1, 9, 13, 124 and 128+ explainedNode.js exit codes: 1 uncaught exception, 5 fatal V8 error, 9 invalid argument, 13 unsettled top-level await, 124 process timeout, 128+n killed by a signal.

Signal table (x86/ARM numbering)

Send a signal

Sources

Related pages