0 - ?
1 - SIGHUP - ?, controlling terminal closed,
2 - SIGINT - interupt process stream, ctrl-C
3 - SIGQUIT - like ctrl-C but with a core dump, interuption by error in code, ctl-/
4 - SIGILL
5 - SIGTRAP
6 - SIGABRT
7 - SIGBUS
8 - SIGFPE
9 - SIGKILL - terminate immediately/hard kill, use when 15 doesn't work or when something disasterous might happen if process is allowed to cont., kill -9
10 - SIGUSR1
11 - SIGEGV
12 - SIGUSR2
13 - SIGPIPE
14 - SIGALRM
15 - SIGTERM - terminate whenever/soft kill, typically sends SIGHUP as well?
16 - SIGSTKFLT
17 - SIGCHLD
18 - SIGCONT - Resume process, ctrl-Z (2nd)
19 - SIGSTOP - Pause the process / free command line, ctrl-Z (1st)
20 - SIGTSTP
21 - SIGTTIN
22 - SIGTTOU
23 - SIGURG
24 - SIGXCPU
25 - SIGXFSZ
26 - SIGVTALRM
27 - SIGPROF
28 - SIGWINCH
29 - SIGIO
29 - SIGPOLL
30 - SIGPWR - shutdown, typically from unusual hardware failure
31 - SIGSYS
First the signals described in the original POSIX.1-1990 standard.
Signal Value Action Comment
──────────────────────────────────────────────────────────────────────
SIGHUP 1 Term Hangup detected on controlling terminal
or death of controlling process
SIGINT 2 Term Interrupt from keyboard
SIGQUIT 3 Core Quit from keyboard
SIGILL 4 Core Illegal Instruction
SIGABRT 6 Core Abort signal from abort(3)
SIGFPE 8 Core Floating point exception
SIGKILL 9 Term Kill signal
SIGSEGV 11 Core Invalid memory reference
SIGPIPE 13 Term Broken pipe: write to pipe with no
readers
SIGALRM 14 Term Timer signal from alarm(2)
SIGTERM 15 Term Termination signal
SIGUSR1 30,10,16 Term User-defined signal 1
SIGUSR2 31,12,17 Term User-defined signal 2
SIGCHLD 20,17,18 Ign Child stopped or terminated
SIGCONT 19,18,25 Cont Continue if stopped
SIGSTOP 17,19,23 Stop Stop process
SIGTSTP 18,20,24 Stop Stop typed at terminal
SIGTTIN 21,21,26 Stop Terminal input for background process
SIGTTOU 22,22,27 Stop Terminal output for background process
The signals SIGKILL and SIGSTOP cannot be caught, blocked, or ignored.
Next the signals not in the POSIX.1-1990 standard but described in
SUSv2 and POSIX.1-2001.
Signal Value Action Comment
────────────────────────────────────────────────────────────────────
SIGBUS 10,7,10 Core Bus error (bad memory access)
SIGPOLL Term Pollable event (Sys V).
Synonym for SIGIO
SIGPROF 27,27,29 Term Profiling timer expired
SIGSYS 12,31,12 Core Bad argument to routine (SVr4)
SIGTRAP 5 Core Trace/breakpoint trap
SIGURG 16,23,21 Ign Urgent condition on socket (4.2BSD)
SIGVTALRM 26,26,28 Term Virtual alarm clock (4.2BSD)
SIGXCPU 24,24,30 Core CPU time limit exceeded (4.2BSD)
SIGXFSZ 25,25,31 Core File size limit exceeded (4.2BSD)
Up to and including Linux 2.2, the default behavior for SIGSYS, SIGX‐
CPU, SIGXFSZ, and (on architectures other than SPARC and MIPS) SIGBUS
was to terminate the process (without a core dump). (On some other
UNIX systems the default action for SIGXCPU and SIGXFSZ is to terminate
the process without a core dump.) Linux 2.4 conforms to the
POSIX.1-2001 requirements for these signals, terminating the process
with a core dump.
Next various other signals.
Signal Value Action Comment
────────────────────────────────────────────────────────────────────
SIGIOT 6 Core IOT trap. A synonym for SIGABRT
SIGEMT 7,-,7 Term
SIGSTKFLT -,16,- Term Stack fault on coprocessor (unused)
SIGIO 23,29,22 Term I/O now possible (4.2BSD)
SIGCLD -,-,18 Ign A synonym for SIGCHLD
SIGPWR 29,30,19 Term Power failure (System V)
SIGINFO 29,-,- A synonym for SIGPWR
SIGLOST -,-,- Term File lock lost (unused)
SIGWINCH 28,28,20 Ign Window resize signal (4.3BSD, Sun)
SIGUNUSED -,31,- Core Synonymous with SIGSYS
(Signal 29 is SIGINFO / SIGPWR on an alpha but SIGLOST on a sparc.)
SIGEMT is not specified in POSIX.1-2001, but nevertheless appears on
most other UNIX systems, where its default action is typically to ter‐
minate the process with a core dump.
SIGPWR (which is not specified in POSIX.1-2001) is typically ignored by
default on those other UNIX systems where it appears.
SIGIO (which is not specified in POSIX.1-2001) is ignored by default on
several other UNIX systems.
Where defined, SIGUNUSED is synonymous with SIGSYS on most architec‐
tures.
