When you run a kill command to stop a process from bash or the javax.realtime.POSIXSignalHandler class, you’re sending what’s known as a POSIX signal to the process. These signals can be called via their numeric representations or the signal (e.g. with the -s option of the kill command). Signals include the following:
- 1: SIGHUP – Close the controlling terminal when the controlling process dies
- 2: SIGINT – Send a keyboard interrupt
- 3: SIGQUIT – Quit from a keyboard/terminal
- 4: SIGILL – Terminate illegal instruction with a core dump and don’t restart
- 5: SIGTRAP – Send a trace/break trap (with core dump)
- 6: SIGABRT – Process an abort signal
- 7: SIGEMT – Send the signal when emulator traps happen
- 8:SIGFPE – Terminate floating point errors (erroneous arithmetic operations) with a core dump
- 9: SIGKILL – Kill a signal outright (kill cannot be ignored)
- 10: SIGBUS – Terminate access (some portion of a memory object) with a core dump
- 11: SIGSEGV – Terminate with a core dump – Invalid memory reference
- 12: SIGSYS – Bad system call
- 13: SIGPIPE – Terminate and write on the pipe
- 14: SIGALRM – Timed kill of a signal
- 15: SIGTERM – Software termination of a signal
- 16: SIGUSR1 – User defined signal 1, with SIGUSR2 as user defined signal 2
- 17: SIGTERM – Software termination of a signal
- 18: SIGCHLD – Child status change
- 19: SIGPWR – Send the signal when the system encounters a power failure
- 20: SIGWINCH – Send the signal to a process when the window changes
- 21: SIGURG – Ignore signal, high bandwidth data
- 22: SIGIO – Terminate pollable event
- 23: SIGSTOP – Stop executing (cannot be ignored or caught by an exception)
- 24: SIGTSTP – Terminate a stop signal.
- 25: SIGCONT – If stopped, continue executing a process
- 26: SIGTTIN – Background process is attempting to read
- 27: SIGTTOU – Background process is attempting to write
- 28: SIGVTALTM – Expired virtual timer
- 29: SIGPROF – Terminate Profiling timer
- 30: SIGXCPU – Past the CPU time limit, terminate with a core dump
- 31: SIGXFSZ – Past the file size limit, terminate with a core dump
- 32: SIGWAITING – Suspend execution of the process until a defined signal is sent
- 33: SIGLWP – Send when the implementing threading requires a signal
- 34: SIGFREEZE – Deprecated
- 35: SIGTHAW – Deprecated
- 36: SIGCANCEL – Deprecated
- 37: SIGLOST – Send the signal when encountering a lost file lock
To put these in practice, let’s use the kill command from bash, with the -s option followed by SIGTERM and then the pid number:
sudo kill -s SIGTERM 20341
