Why does kill sometimes not work?

The default kill sends SIGTERM (15) — a polite request the process can ignore or trap. If the process doesn't exit, escalate to SIGKILL (9): kill -9 . SIGKILL can't be trapped, blocked, or ignored — the kernel terminates the process immediately.

What's the difference between SIGINT and SIGTERM?

SIGINT (2) is what Ctrl+C sends — interactive interrupt. SIGTERM (15) is the standard 'please exit' signal sent by kill. Both are catchable; processes typically handle them with the same cleanup logic.

When do I see SIGSEGV?

SIGSEGV (11) means the process accessed memory it doesn't own — a null pointer deref, buffer overflow, or stack overflow. The default action is to dump core and terminate. Common cause: programming bug in C/C++/Rust unsafe code.

posix signals · linux · default actions · local

POSIX signal reference

Searchable table of POSIX signals with numbers, default actions, descriptions, and typical uses. Send with kill -SIGNAL pid or kill -N pid (numbers differ on non-Linux).

Linux Signal Reference

31 matches

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all

Total

signals

Actions

defaults

Status

ready

local

signal table

#	Default	Description
1	Term	Hangup detected on controlling terminal.
2	Term	Interrupt from keyboard (Ctrl-C).
3	Core	Quit from keyboard (Ctrl-\).
4	Core	Illegal instruction.
5	Core	Trace/breakpoint trap.
6	Core	Abort signal from abort(3).
7	Core	Bus error (bad memory access alignment).
8	Core	Floating-point exception.
9	Term	Kill signal (cannot be caught or ignored).
10	Term	User-defined signal 1.
11	Core	Invalid memory reference (segmentation fault).
12	Term	User-defined signal 2.
13	Term	Broken pipe: write to pipe with no readers.
14	Term	Timer signal from alarm(2).
15	Term	Termination request — default for kill(1).
16	Term	Stack fault on coprocessor (rarely used).
17	Ign	Child process stopped or terminated.
18	Cont	Continue if stopped.
19	Stop	Stop process (cannot be caught or ignored).
20	Stop	Stop typed at terminal (Ctrl-Z).
21	Stop	Background process attempting read from tty.
22	Stop	Background process attempting write to tty.
23	Ign	Urgent condition on socket.
24	Core	CPU time limit exceeded.
25	Core	File size limit exceeded.
26	Term	Virtual alarm clock.
27	Term	Profiling timer expired.
28	Ign	Window resize signal.
29	Term	I/O now possible (POLL).
30	Term	Power failure imminent.
31	Core	Bad system call.

typical uses & defaults

Default actions

Term · Default: terminate the process.

Core · Default: terminate the process and dump core.

Ign · Default: ignore the signal.

Stop · Default: stop the process.

Cont · Default: continue if stopped.

Typical uses

SIGHUP · Daemons often reload config on SIGHUP.

SIGINT · Stop foreground process gracefully.

SIGQUIT · Stop process and dump core for debugging.

SIGILL · Generated by CPU on bad opcode — usually a bug.

SIGTRAP · Used by debuggers (gdb breakpoints).

SIGABRT · assert() failure or explicit abort().

SIGBUS · Unaligned access or mmap'd file truncated.

SIGFPE · Divide-by-zero or invalid math op.

SIGKILL · Last resort to terminate a stuck process.

SIGUSR1 · App-specific — often used to trigger log rotation, etc.

SIGSEGV · Null pointer / out-of-bounds access.

SIGUSR2 · App-specific — second custom hook.

SIGPIPE · Common in shell pipelines when reader exits early.

SIGALRM · Implements timeouts in POSIX code.

SIGTERM · Polite shutdown signal; let process clean up.

SIGSTKFLT · Legacy — typically unused on modern Linux.

SIGCHLD · Parent reaps zombies with wait(2).

SIGCONT · Resume a process previously stopped.

SIGSTOP · Force-pause a process from outside.

SIGTSTP · Suspend job to background; resume with fg/bg.

SIGTTIN · Job control: bg process needs terminal input.

SIGTTOU · Job control: bg process tried to write to terminal.

SIGURG · TCP out-of-band data received.

SIGXCPU · Process exceeded RLIMIT_CPU.

SIGXFSZ · Wrote past RLIMIT_FSIZE.

SIGVTALRM · Timer that counts process CPU time only.

SIGPROF · Used by profilers (gprof).

SIGWINCH · Terminal apps redraw on window resize.

SIGIO · Asynchronous I/O notification.

SIGPWR · UPS daemons notify processes.

SIGSYS · Seccomp filter rejection or unknown syscall.

Quick Start

How signals work

Each process can receive numbered signals. SIGTERM (15) politely asks to quit; SIGKILL (9) is unstoppable; SIGSTOP/CONT pause and resume.

01
Find the signal
Search by name (SIGTERM), number (15), or description.
Inputs are treated as UTF-8 throughout the pipeline and validated client-side as you type — nothing dispatches until the value is well-formed.
searchinpututf-8client-sidevalidated
search · textterm · set
```
SIGTERM (15)
```
loaded · parsedclient-side
02
Read default action
Term, Core, Ign, Stop, Cont — color-coded.
Each toggle re-computes through a memoised hook, so flipping options never resets your input and the UI stays snappy on large inputs.
actionoptionslivememoisedtoggles
default · memoisedTerm · live
```
process exits
```
options set · memoisedlive
03
Send the signal
kill -15 1234, kill -SIGTERM 1234, or kill 1234 (default 15).
Randomness — where used — comes from crypto.getRandomValues, never Math.random. Heavy work sits in useMemo.
sendcomputeinstantlocaldeterministic
send · instantkill · computed
```
kill -TERM 1234
```
computed · instantinstant
04
Copy name
Click any signal name to copy.
Copy writes through navigator.clipboard and downloads use a Blob — zero network traffic. Same input plus same options always yield the same bytes.
copydownloadzero-networkreproducible
ok · copiedready · copied
```
Copied SIGTERM
```
shipped · ready to shipsuccess

Pro tips

Pro tips for everyday utilities

Reach for crypto.getRandomValues

Cryptographically random for IDs, tokens, salts. Math.random is for animation and games, not security.

Sort IDs lexicographically

UUID v4 has no time ordering. Use ULID or UUID v7 if you need sorted IDs.

Mock data with seeds

Faker-style libraries can be seeded so tests are reproducible. Embed the seed in the fixture file.

Reference cards beat memory

Cheatsheets for Vim, Git, Docker, Linux signals are faster than man pages when you’re mid-flow.

Browser APIs vary

Touch events, gamepads, and clipboard differ across vendors. Feature-detect before use.

Persist in the right place

localStorage for user preferences, sessionStorage for transient state, IndexedDB for structured data.

Use Cases

When to look up signals

Process management, daemon control, debugging.

Daemon reload

SIGHUP is the typical 'reload config' signal. Random values come from crypto.getRandomValues — cryptographically secure for tokens, salts, and session IDs. Math.random is deterministic enough for animations but predictable enough to be a security bug.

CSPRNG-backed

Graceful shutdown

SIGTERM first, SIGKILL only if needed. Pair with hashids, ULID, or UUID v7 when you need both random and sortable — useful for primary keys, public-facing IDs, and event log ordering without a sequence column.

reproducible

Debugging

SIGSEGV vs SIGBUS reveals memory bug class. Output is deterministic given the same seed, so fixtures and tests stay reproducible across CI runs and contributor machines. Embed the seed in the fixture file for full replay.

snappy

Container exits

Docker stop sends SIGTERM, then SIGKILL after 10s. Heavy work runs through useMemo so the UI stays snappy on large inputs. Same input + same options yields identical bytes — the kind of stability snapshot tests rely on.

feature-detected

Job control

Ctrl-Z → SIGTSTP; fg/bg send SIGCONT. Storage tools persist to the right backend: localStorage for user preferences, sessionStorage for transient state, IndexedDB for structured data. Pick the right shelf and quota worries disappear.

deterministic

Cross-platform notes

Numbers differ on macOS/BSD; names match. Browser feature detection: clipboard, fullscreen, gamepad, and Web Bluetooth APIs gracefully fall back when unavailable. No surprise white screens on Safari or older Firefox.

production-ready

FAQ

Frequently asked questions

Why are some signals uncatchable?

SIGKILL and SIGSTOP can't be handled by a process — the kernel enforces them so init can always reclaim runaway processes.

Is signal 9 always kill?

On Linux yes; macOS/BSD use the same number. Some platforms differ — prefer SIGKILL by name.

Where do real-time signals fit?

SIGRTMIN..SIGRTMAX (typically 34-64) are user-defined real-time signals. Not listed here.

How do I send to a whole group?

kill -SIGNAL -PGID — note the negative PID.

Does it run locally?

Yes — the reference is bundled in JS. Nothing is sent to a server.

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