Linux signals

Signals are messages that are sent to a program.

Here are some Linux signals in brief detail. You may quickly list available signals by running kill -l.

Signal Name	Signal Number	Description
SIGHUP	1	Hangs up signals when controlling the terminal or at the end of the controlling processes.
SIGINT	2	Signals when the Linux user presses Ctrl-c
SIGQUIT	3	Signals when the Linux user presses Ctrl-d
SIGILL	4	Illegal instruction trap
SIGTRAP	5	Trap or breakpoint signal
SIGABRT	6	Abort signal
SIGBUS	7	Illegal access to an undefined portion of memory
SIGFPE	8	Signals when any unexpected mathematical operation is performed.
SIGKILL	9	When any of the process issues this signal, it will quit immediately.
SIGUSR1	10	User defined signal. Typically programs will print its status (eg. dd)
SIGSEGV	11	Segmentation fault
SIGUSR2	12	User defined signal.
SIGPIPE	13	Write on a pipe with no one to read it
SIGALRM	14	Signals for alarm clock
SIGTERM	15	Signals to terminate the process or the software.
SIGSTKFLT	16	Stack fault
SIGSTOP	17	Signals to stop the process in Linux.
SIGCONT	18	Resume program execution from a SIGSTOP or SIGTSTP.
SIGSTOP	19	Stop signal sent with kill -STOP to suspend a program. Cannot be ignored by the program.
SIGTSTP	20	Signals when the Linux user presses Ctrl-z. May be ignored by the program.
SIGTTIN	21	Delivered to a background process if it tries to read from the terminal.
SIGTTOU	22	Delivered to a background process if it tries to write to the terminal.
SIGURG	23	Urgent data received on a socket.
SIGXCPU	24	Process exceeds CPU limit or time. Save your work before you get killed.
SIGXFSZ	25	File written by this process exceeded some size limit.
SIGVTALRM	26	CPU time elapsed
SIGPROF	27
SIGWINCH	28	Window size changed.
SIGIO	29	Signal input/output trap. Program should abort unless handled properly.
SIGPWR	30	Power failure?
SIGSYS	31	Bad system call

See also

• Wikipedia's article outlines all the signals and their default actions: https://en.wikipedia.org/wiki/Signal_(IPC)