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Unix Signals Reference

Searchable reference of standard Linux signals with default actions, catchability, and exit status codes.

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Signal / exit status lookup

Signal number (1-31), name, or exit status (129-159)

Unix signals reference table

Number	Signal name	Default action	Catchable	Exit status	Note
1	1SIGHUP	Terminate	Yes	129	Hangup detected on the controlling terminal, or the controlling process died. Many daemons reload their configuration on SIGHUP, but that is only a convention each program chooses, not a kernel definition. TerminateCatchable: YesExit status: 129
2	2SIGINT	Terminate	Yes	130	Interrupt from the keyboard, usually Ctrl+C. TerminateCatchable: YesExit status: 130
3	3SIGQUIT	Terminate + core dump	Yes	131	Quit from the keyboard, usually Ctrl+\. By default it also writes a core dump. Terminate + core dumpCatchable: YesExit status: 131
4	4SIGILL	Terminate + core dump	Yes	132	Illegal instruction: the process tried to execute an invalid machine instruction. Terminate + core dumpCatchable: YesExit status: 132
5	5SIGTRAP	Terminate + core dump	Yes	133	Trace or breakpoint trap, used by debuggers. Terminate + core dumpCatchable: YesExit status: 133
6	6SIGABRT	Terminate + core dump	Yes	134	Abort signal, as raised by abort(3), for example after a failed assertion. SIGIOT is the same number. Terminate + core dumpCatchable: YesExit status: 134
7	7SIGBUS	Terminate + core dump	Yes	135	Bus error: a bad memory access, for example beyond the end of a memory-mapped file. Terminate + core dumpCatchable: YesExit status: 135
8	8SIGFPE	Terminate + core dump	Yes	136	Erroneous arithmetic operation, such as integer division by zero; despite the name, not only floating point. Terminate + core dumpCatchable: YesExit status: 136
9	9SIGKILL	Terminate	No	137	Kills the process. It cannot be caught, blocked, or ignored, so the program gets no chance to clean up. TerminateCatchable: NoExit status: 137
10	10SIGUSR1	Terminate	Yes	138	User-defined signal 1; its meaning is up to each program. TerminateCatchable: YesExit status: 138
11	11SIGSEGV	Terminate + core dump	Yes	139	Invalid memory reference (segmentation fault). Terminate + core dumpCatchable: YesExit status: 139
12	12SIGUSR2	Terminate	Yes	140	User-defined signal 2; its meaning is up to each program. TerminateCatchable: YesExit status: 140
13	13SIGPIPE	Terminate	Yes	141	Broken pipe: a write to a pipe with no reader, for example after the reading process exited. TerminateCatchable: YesExit status: 141
14	14SIGALRM	Terminate	Yes	142	Timer signal from alarm(2). TerminateCatchable: YesExit status: 142
15	15SIGTERM	Terminate	Yes	143	Termination request; the default signal sent by kill(1). Unlike SIGKILL it can be caught, so the program can shut down cleanly. TerminateCatchable: YesExit status: 143
16	16SIGSTKFLT	Terminate	Yes	144	Stack fault on a coprocessor. Linux-specific and unused. TerminateCatchable: YesExit status: 144
17	17SIGCHLD	Ignore	Yes	145	A child process stopped, terminated, or continued. Ignored by default. IgnoreCatchable: YesExit status: 145
18	18SIGCONT	Continue	Yes	146	Continues the process if it is stopped. ContinueCatchable: YesExit status: 146
19	19SIGSTOP	Stop	No	147	Stops the process. It cannot be caught, blocked, or ignored; SIGCONT resumes it. StopCatchable: NoExit status: 147
20	20SIGTSTP	Stop	Yes	148	Stop typed at the terminal, usually Ctrl+Z. Unlike SIGSTOP it can be caught. StopCatchable: YesExit status: 148
21	21SIGTTIN	Stop	Yes	149	A background process tried to read from its terminal. StopCatchable: YesExit status: 149
22	22SIGTTOU	Stop	Yes	150	A background process tried to write to its terminal. StopCatchable: YesExit status: 150
23	23SIGURG	Ignore	Yes	151	Urgent condition on a socket, such as out-of-band data. IgnoreCatchable: YesExit status: 151
24	24SIGXCPU	Terminate + core dump	Yes	152	CPU time limit exceeded (see setrlimit(2)). Terminate + core dumpCatchable: YesExit status: 152
25	25SIGXFSZ	Terminate + core dump	Yes	153	File size limit exceeded (see setrlimit(2)). Terminate + core dumpCatchable: YesExit status: 153
26	26SIGVTALRM	Terminate	Yes	154	Virtual alarm clock: a timer that counts only the user-mode CPU time of the process. TerminateCatchable: YesExit status: 154
27	27SIGPROF	Terminate	Yes	155	Profiling timer expired; that timer counts both user and system CPU time. TerminateCatchable: YesExit status: 155
28	28SIGWINCH	Ignore	Yes	156	The terminal window size changed. Ignored by default. IgnoreCatchable: YesExit status: 156
29	29SIGIO	Terminate	Yes	157	I/O is now possible on a file descriptor set up for signal-driven I/O. SIGPOLL is the same number. TerminateCatchable: YesExit status: 157
30	30SIGPWR	Terminate	Yes	158	Power failure (System V). Linux terminates by default; other UNIX systems typically ignore it. TerminateCatchable: YesExit status: 158
31	31SIGSYS	Terminate + core dump	Yes	159	Bad system call; also raised by seccomp(2) filters. SIGUNUSED is the same number. Terminate + core dumpCatchable: YesExit status: 159

How it works

A reference of the standard Linux signals 1-31 with their default actions, whether they can be caught or blocked, and the exit status a process receives when killed by each signal. Each signal has a note in English and Japanese on what raises it or what it is for; the filter matches words from either language. Real-time signals (32-64 in the kernel; glibc moves SIGRTMIN to 34 or 35) have no predefined meaning and are not listed. These signal numbers follow the Linux asm-generic definitions used on x86-64, ARM, and most architectures; Alpha, SPARC, MIPS, and PA-RISC assign several signals different numbers. Use `kill -l` on your target machine to verify. The SIGHUP meaning of "reload configuration" is a convention individual daemons chose, not a kernel definition. Exit-status lookup accepts values 129-159 (128 + 1-31) and reports the corresponding signal; the formula 128 + signal number is a bash/shell convention and not a kernel value, so an ordinary program is free to exit with 137 for any reason.

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