Linux Kill Process Signals

SIGHUP

hangup - this is sent to a process when the terminal that controls it is closed

SIGINT

interrupt - sent when a user presses [Ctrl] + C in the controlling terminal to interrupt a process

SIGQUIT

quit - sent when a user presses [Ctrl] + D to quit

SIGKILL

kill - immediately kill a process with no clean-up operations

SIGTERM

terminate - program termination

SIGSTOP

Stop the program. It cannot be handled anymore.

SIGTSTP

temporary stop - sent when a user presses [Ctrl] + Z to request for a service to suspend. The user can handle it afterward

what’s the syntax for sending a <signal> to a process?

SIGILL

illegal instruction - triggered when a process attempts to execute an invalid, unknown, or privileged CPU instruction.

SIGTRAP

breakpoint trap / trace - used by debuggers (like gdb) to pause a program at a specific point

SIGABRT

abort - sent by the process itself when it calls the abort() function, usually due to a critical software failure or failed assertion

SIGBUS

bus error - indicates a hardware-level memory access error, such as misaligned memory access or referencing non-existent physical space

SIGFPE

floating-point exception - triggered by erroneous arithmetic operations like division by zero or arithmetic overflow

SIGUSR1

user-defined signal 1 - left entirely to developers to define custom behaviors within their programs

SIGSEGV

segmentation fault - triggered when a program attempts to access a memory location it is not allowed to (e.g., dereferencing a null pointer)

SIGUSR2

user-defined signal 2 - the second custom-purpose signal available for applications

SIGPIPE

broken pipe - sent to a process trying to write data to a pipe or socket that has already been closed by the reader on the other end

SIGALRM

alarm clock - sent when a timer set by the alarm() system call expires; used for time-outs

SIGSTKFLT

stack fault - historically used for coprocessor stack faults on older architectures; rarely used on modern systems

SIGCHLD

child status changed - sent to a parent process whenever one of its child processes terminates, stops, or resumes

SIGCONT

continue - instructs a process to resume execution if it was previously paused by a stop signal

SIGTTIN

“attempted terminal input” background read - sent to a background process if it attempts to read input from its controlling terminal

SIGTTOU

“attempted terminal output” background write - sent to a background process if it attempts to write output to its controlling terminal

SIGURG

urgent data - sent when urgent or out-of-band data is available on a network socket

SIGXCPU

exceeded CPU time limit - sent when a process exceeds its maximum allowed CPU allocation

SIGXFSZ

exceeded file size limit - sent when a process attempts to grow a file beyond the maximum allowed limit

SIGVTALRM

virtual alarm/timer expired - sent when a virtual timer expires (measuring only CPU time used by the process)

SIGPROF

profiling timer expired - sent when a profiling timer expires (measuring both process CPU time and system CPU time)

SIGWINCH

window change/resize - sent to a foreground terminal process when the size of its terminal window changes

SIGIO (SIGPOLL)

I/O possible - sent when a file descriptor is ready for input or output operations

SIGPWR

power failure - sent by power management systems to indicate a power loss or UPS battery event, signaling the system to save data and shut down

SIGSYS

bad system call - sent when a program passes an invalid or unimplemented argument to a system call

Signals 34 - 64

Real-Time Signals - no standard system meanings; reserved entirely for custom, application-level signaling

34-49: SIGRTMIN to SIGRTMIN+15

50-64: SIGRTMAX-14 to SIGRTMAX

Signals 1 - 31

Standard Signals