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Module: Signal

Relationships & Source Files
Defined in: signal.c

Overview

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"
  end
  Signal.trap("TERM") do
    puts "Terminating..."
    shutdown()
  end
  # . . . do some work . . .
end

Process.detach(pid)

# Controlling program:
Process.kill("USR1", pid)
# ...
Process.kill("USR1", pid)
# ...
Process.kill("TERM", pid)

produces:

 Debug now: true
 Debug now: false
Terminating...

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.

Class Method Summary

Class Method Details

.listHash (mod_func)

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}
[ GitHub ]

  
# File 'signal.c', line 1448

static VALUE
sig_list(void)
{
    VALUE h = rb_hash_new();
    const struct signals *sigs;

    FOREACH_SIGNAL(sigs, 0) {
	rb_hash_aset(h, rb_fstring_cstr(sigs->signm), INT2FIX(sigs->signo));
    }
    return h;
}

.signame(signo) ⇒ String? (mod_func)

Convert signal number to signal name. Returns nil if the signo is an invalid signal number.

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

produces:

INT
[ GitHub ]

  
# File 'signal.c', line 301

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(*args) (mod_func)

Alias for Kernel.trap.