From: Joe Van Dyk <joevandyk@...>
Date: 2006-09-27T07:03:35+09:00
Subject: Re: forking processes and writing to log file

On 9/26/06, Gennady Bystritsky <Gennady.Bystritsky@quest.com> wrote:
> Joe Van Dyk wrote:
> > On 9/26/06, Joe Van Dyk <joevandyk@gmail.com> wrote:
> >> Hello,
> >>
> >> So, on linux, I'm forking a new Ruby process.  I redirect stdout and
> >> stderr into a file and then I execute another program via 'system'.
> >
> > I should probably mention that the other program that's being executed
> > is rsh, which executes a command on a different machine.
>
> You either did not redirect stdout/stderr to a file properly, or
> something you execute tries to output directly to the controlling
> terminal (/dev/tty). You can disassosiate your spawned process from a
> controlling terminal, just to be sure (not with 'system' though):
>
> logfile = "my_log_file.log"
> pid = fork do
>   File.open(logfile, 'w') do |_io|
>     $stdout.reopen(_io)
>     $stderr.reopen(_io)
>   end
>
>   Process.setsess # In this scenario disassociates the controlling
>                   # terminal until another tty device is open (will
>                   # become new controlling tty).
>
>   exec "the_command_line_used_to_be_launched_by_system"
> end
>
> Process.waitpid pid

I assume you mean Process.setsid?

I have this function called at the beginning of the fork:
# Redirect stdout and stderr to a file and flush the buffers on a write
def redirect_all_output_to_file file
   log = File.new(file, "w+")
   STDOUT.reopen log;  STDERR.reopen log
   STDOUT.sync = true
end

When I add Process.setsid to the end of that function, when I
background the ruby process, stuff keeps writing to the log file, but
my controlling terminal gets all messed up.  The only keys on my
keyboard that work are 'e', 's', the space bar, and the backspace key,
and they only work half the time.  The terminal works normally once
the ruby process is killed.