Module: Signal (Ruby 2.3.4)

    In Files

    • signal.c

    Class/Module Index [+]



    Many operating systems allow signals to be sent to running processes. Some signals have a defined effect on the process, while others may be trapped at the code level and acted upon. For example, your process may trap the USR1 signal and use it to toggle debugging, and may use TERM to initiate a controlled shutdown.

    pid = fork do
      Signal.trap("USR1") do
        $debug = !$debug
        puts "Debug now: #$debug"
      Signal.trap("TERM") do
        puts "Terminating..."
      # . . . do some work . . .
    # Controlling program:
    Process.kill("USR1", pid)
    # ...
    Process.kill("USR1", pid)
    # ...
    Process.kill("TERM", pid)


     Debug now: true
     Debug now: false

    The list of available signal names and their interpretation is system dependent. Signal delivery semantics may also vary between systems; in particular signal delivery may not always be reliable.

    Public Class Methods

    list → a_hash click to toggle source

    Returns a list of signal names mapped to the corresponding underlying signal numbers.

    Signal.list   #=> {"EXIT"=>0, "HUP"=>1, "INT"=>2, "QUIT"=>3, "ILL"=>4, "TRAP"=>5, "IOT"=>6, "ABRT"=>6, "FPE"=>8, "KILL"=>9, "BUS"=>7, "SEGV"=>11, "SYS"=>31, "PIPE"=>13, "ALRM"=>14, "TERM"=>15, "URG"=>23, "STOP"=>19, "TSTP"=>20, "CONT"=>18, "CHLD"=>17, "CLD"=>17, "TTIN"=>21, "TTOU"=>22, "IO"=>29, "XCPU"=>24, "XFSZ"=>25, "VTALRM"=>26, "PROF"=>27, "WINCH"=>28, "USR1"=>10, "USR2"=>12, "PWR"=>30, "POLL"=>29}
                   static VALUE
        VALUE h = rb_hash_new();
        const struct signals *sigs;
        for (sigs = siglist; sigs->signm; sigs++) {
            rb_hash_aset(h, rb_str_new2(sigs->signm), INT2FIX(sigs->signo));
        return h;
    signame(signo) → string click to toggle source

    convert signal number to signal name

    Signal.trap("INT") { |signo| puts Signal.signame(signo) }
    Process.kill("INT", 0)


                   static VALUE
    sig_signame(VALUE recv, VALUE signo)
        const char *signame = signo2signm(NUM2INT(signo));
        if (!signame) return Qnil;
        return rb_str_new_cstr(signame);
    trap( signal, command ) → obj click to toggle source
    trap( signal ) {| | block } → obj

    Specifies the handling of signals. The first parameter is a signal name (a string such as “SIGALRM”, “SIGUSR1”, and so on) or a signal number. The characters “SIG” may be omitted from the signal name. The command or block specifies code to be run when the signal is raised. If the command is the string “IGNORE” or “SIG_IGN”, the signal will be ignored. If the command is “DEFAULT” or “SIG_DFL”, the Ruby’s default handler will be invoked. If the command is “EXIT”, the script will be terminated by the signal. If the command is “SYSTEM_DEFAULT”, the operating system’s default handler will be invoked. Otherwise, the given command or block will be run. The special signal name “EXIT” or signal number zero will be invoked just prior to program termination. trap returns the previous handler for the given signal.

    Signal.trap(0, proc { puts "Terminating: #{$$}" })
    Signal.trap("CLD")  { puts "Child died" }
    fork && Process.wait


    Terminating: 27461
    Child died
    Terminating: 27460
                   static VALUE
    sig_trap(int argc, VALUE *argv)
        int sig;
        sighandler_t func;
        VALUE cmd;
        rb_check_arity(argc, 1, 2);
        sig = trap_signm(argv[0]);
        if (reserved_signal_p(sig)) {
            const char *name = signo2signm(sig);
            if (name)
                rb_raise(rb_eArgError, "can't trap reserved signal: SIG%s", name);
                rb_raise(rb_eArgError, "can't trap reserved signal: %d", sig);
        if (argc == 1) {
            cmd = rb_block_proc();
            func = sighandler;
        else {
            cmd = argv[1];
            func = trap_handler(&cmd, sig);
        if (OBJ_TAINTED(cmd)) {
            rb_raise(rb_eSecurityError, "Insecure: tainted signal trap");
        return trap(sig, func, cmd);