topic Re: how to detach a process from the assigned tty? in Operating System - HP-UX

how to detach a process from the assigned tty?

Laurent Laperrousaz — Thu, 12 Jun 2003 14:07:38 GMT

Hello,

Does anybody know how I can detach a process from its tty?

I can't find a way!

Laurent

Re: how to detach a process from the assigned tty?

John Meissner — Thu, 12 Jun 2003 14:13:34 GMT

could you give an example of what you mean?

Re: how to detach a process from the assigned tty?

David_246 — Thu, 12 Jun 2003 14:14:39 GMT

Sorry, not possible.
You could try the kill -HUP function, but please be carefull.

Regs David

Re: how to detach a process from the assigned tty?

John Meissner — Thu, 12 Jun 2003 14:15:32 GMT

If you are trying to output to a different tty you could use the write command

write 'message' tty

Re: how to detach a process from the assigned tty?

Umapathy S — Thu, 12 Jun 2003 14:25:02 GMT

Laurent,

I know this to do programmatically. Normally when daemons are created they will detach themselves from the tty which started it for they can run in the background, free from any signals from the tty, etc.

HTH,
Umapathy

Re: how to detach a process from the assigned tty?

A. Clay Stephenson — Thu, 12 Jun 2003 14:25:53 GMT

If you mean, can you detach stdin, stdout, and stderr from a running process and somehow recoonect to another device - possibly /dev/null - then no this can't be done.

It is easy from the programming level. You use setsid(); it's one of the basic things you do to "daemonize" a process in C or Perl.

You can also look into the nohup command but all of these assume that you do this "on the front end" not after the process has been started.

Re: how to detach a process from the assigned tty?

Massimo Bianchi — Thu, 12 Jun 2003 14:50:52 GMT

Hi,
depending on what do you want to do, you have two solution:

- if unattended: start your job with a "nohup" at the beginning and an "&" at the end. This ways it will continue to work even if the tty is closed.

- if attended: install a tool like "screen", it can attach and detach from its sessions.
ctrl-a,d detach from current session

screen -l reattach to a detached session.

see the man for more details...

Downloadable free from

http://hpux.connect.org.uk/

HTH,

Massimo

Re: how to detach a process from the assigned tty?

Massimo Bianchi — Thu, 12 Jun 2003 14:52:00 GMT

Direct link:

http://hpux.connect.org.uk/hppd/hpux/Sysadmin/screen-3.9.11/

HTH,
Massimo

Re: how to detach a process from the assigned tty?

Laurent Laperrousaz — Thu, 12 Jun 2003 15:35:15 GMT

thanks everybody!

In fact what I want is to demonize a process launched at startup through /sbin/init.d/myprocess

It appeared that it starts but fails later because of inittab getty console init.

myprocess appears to be attached to the system console and it forks a lot of processes (all are then attached to the console). When getty init the console (that happens after init.d due to inittab sequence) all my processes stop!

I think the setsid() is the solution I will try to use it in a perl script and let you know how it works!

Re: how to detach a process from the assigned tty?

A. Clay Stephenson — Thu, 12 Jun 2003 15:51:54 GMT

Okay Laurent, now that I know what you are trying to do, I specnt about 2 minutes chopping up one of my Perl daemons. It has pretty much all the steps including a signal handler to exit when it receives a SIGTERM (kill -15).