Did You Know?

Each process is controlled by sending signals to it which tell it what to do. This is how the kill command has its effect; by sending a process a signal which tells it to stop, hang up or terminate etc.

You can list the different types of signal that can be sent to a process by using the kill command together with its -l option. For example:

   kill -l
    1) SIGHUP       2) SIGINT       3) SIGQUIT      4) SIGILL
    5) SIGTRAP      6) SIGIOT       7) SIGEMT       8) SIGFPE
    9) SIGKILL     10) SIGBUS      11) SIGSEGV     12) SIGSYS
   13) SIGPIPE     14) SIGALRM     15) SIGTERM     16) SIGUSR1
   17) SIGUSR2     18) SIGCHLD     19) SIGPWR      20) SIGWINCH
   21) SIGURG      22) SIGIO       23) SIGSTOP     24) SIGTSTP
   25) SIGCONT     26) SIGTTIN     27) SIGTTOU     28) SIGVTALRM
   29) SIGPROF

Signal type 1 (one) will send a process a signal to hang up (SIGHUP): signal type 9 (nine) is a signal to kill (SIGKILL) the process. This is certain to kill it.