kill(*args) public

Sends the given signal to the specified process id(s) if pid is positive. If pid is zero signal is sent to all processes whose group ID is equal to the group ID of the process. signal may be an integer signal number or a POSIX signal name (either with or without a SIG prefix). If signal is negative (or starts with a minus sign), kills process groups instead of processes. Not all signals are available on all platforms. The keys and values of Signal.list are known signal names and numbers, respectively.

pid = fork do
   Signal.trap("HUP") { puts "Ouch!"; exit }
   # ... do some work ...
end
# ...
Process.kill("HUP", pid)
Process.wait

produces:

Ouch!

If signal is an integer but wrong for signal, Errno::EINVAL or RangeError will be raised. Otherwise unless signal is a String or a Symbol, and a known signal name, ArgumentError will be raised.

Also, Errno::ESRCH or RangeError for invalid pid, Errno::EPERM when failed because of no privilege, will be raised. In these cases, signals may have been sent to preceding processes.

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August 11, 2009
2 thanks

Common signals

Some of the more commonly used signals:

1       HUP (hang up)
2       INT (interrupt)
3       QUIT (quit)
6       ABRT (abort)
9       KILL (non-catchable, non-ignorable kill)
14      ALRM (alarm clock)
15      TERM (software termination signal)
December 29, 2011
0 thanks

Use kill 0 to find out if process is running

is_running.rb:

#!/usr/bin/env ruby

pid = ARGV[0].to_i

begin
  Process.kill(0, pid)
  puts "#{pid} is running"
rescue Errno::EPERM                     # changed uid
  puts "No permission to query #{pid}!";
rescue Errno::ESRCH
  puts "#{pid} is NOT running.";      # or zombied
rescue
  puts "Unable to determine status for #{pid} : #{$!}"
end

Thanks to http://stackoverflow.com/a/200568/51209