kill

Send a signal to a process by PID.

Description

Sends a signal to one or more processes (or process groups) identified by PID. Without a signal flag, sends SIGTERM. Also exposes the canonical signal table via -l and -L, so it can be used to convert between signal names and numbers without sending anything.

Inputs

kill(2) syscall via libc::kill for delivery.
No /proc access; PIDs are passed straight through to the kernel.

Synopses

kill [options] <pid> [<pid> ...]
kill -l [<signal> ...]
kill -L

Arguments

Flag	Description
`-s, --signal SIG`	Signal to send – name or number. Default: `TERM`
`-<SIG>` (e.g. `-9`, `-KILL`, `-SIGKILL`)	Same as `-s SIG`. Equivalent forms; the leading `-` plus signal spec is consumed if `-s` was not given
`-l, --list [SIG ...]`	List signal names. With no arguments, prints all signal names separated by spaces. With arguments, converts each from name to number or number to name (one per line)
`-L, --table`	Print the signal table – number and name pairs, eight per line
`--help`	Print help
`-V, --version`	Print version
`--`	End of options; subsequent arguments are PIDs even if they start with `-`
`<pid>`	One or more PIDs to signal (see semantics below)

PID semantics

Following kill(2):

PID	Effect
`> 0`	Signal the process with that PID
`0`	Signal every process in the caller’s process group
`-1`	Signal every process the caller is permitted to signal, except `init`
`< -1`	Signal every process in the process group with PID `\|pid\|`

A negative PID that follows -- is parsed as a PID. Without --, a leading negative argument is consumed as the signal spec when -s was not given.

Behavior

Signal selection precedence

-s SIG / --signal SIG
A leading -N or -NAME argument (e.g. kill -9 1234, kill -KILL 1234)
Default: TERM

Signal 0 is the null signal – delivery is checked but no signal is sent. kill -0 PID is the standard way to test whether a process exists and is signalable by the caller.

`-l` / `--list`

Invocation	Output
`kill -l`	All signal names (no `SIG` prefix), space-separated, one line
`kill -l N`	Name for signal number `N`
`kill -l NAME`	Number for signal name (with or without `SIG` prefix)
`kill -l N1 N2 ...`	Each conversion on its own line

`-L` / `--table`

Prints the signal table eight pairs per line, formatted as:

 1 HUP   2 INT   3 QUIT   4 ILL   5 TRAP   6 ABRT   7 BUS   8 FPE
 9 KILL 10 USR1 11 SEGV 12 USR2 13 PIPE 14 ALRM 15 TERM 16 STKFLT
...

Supported signals

Standard signals 1–31 (HUP, INT, QUIT, ILL, TRAP, ABRT/IOT, BUS, FPE, KILL, USR1, SEGV, USR2, PIPE, ALRM, TERM, STKFLT, CHLD/CLD, CONT, STOP, TSTP, TTIN, TTOU, URG, XCPU, XFSZ, VTALRM, PROF, WINCH, IO/POLL, PWR, SYS). Real-time signals (SIGRTMIN..SIGRTMAX) are not yet listed by -l or -L but can still be sent by number.

Exit codes

Code	Meaning
0	All signals delivered successfully (or a successful list/table operation)
1	At least one signal delivery failed (no such process, permission denied, etc.)
2	Usage error (unknown signal, no PIDs given, invalid PID)

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