topic Re: init.rc script fails because tty detach in Operating System - Linux

init.rc script fails because tty detach

manoj_pu — Fri, 15 Jul 2005 18:43:56 GMT

we tried to set an init script to start an application on system boot using an init script (rc).

The process starts but is killed by the next inittab line: getty console.

Is there any way to "demonize" the process and then detach it from the console.

I tried to "nohup" the script but it fails to detach the process from console.

Manoj

Re: init.rc script fails because tty detach

Sudeesh — Fri, 15 Jul 2005 19:35:50 GMT

I couldn't understand why you want to start the script using inittab entry, is it a specific requirement?

May be your script is starting the process too early (that means at a point where other necessary system process still to start) and thats why it is getting killed.

Try starting the script manually after the system is booted. If this works fine put your script in /sbin/init.d folder and then create a link from /sbin/rc2.d. Adjust the link name so as to run it at the last of run level 2. Link name should be in Sxxx format.

Hope this helps

Sudeesh

Re: init.rc script fails because tty detach

Mel Burslan — Fri, 15 Jul 2005 20:08:44 GMT

does your process have a need for console access ? And why does it need to start before the console getty process ? Or is it getting killed because it is conflicting with getty for console resource ?

I am not sure what process needs to be started this early in the boot-up sequence but if you just time the start of your program, and run it on the background with nohup, there should not be any problems.

Re: init.rc script fails because tty detach

Stuart Browne — Sun, 17 Jul 2005 06:28:30 GMT

So doing a 'nohup &' doesn't work?

What are you trying to daemonize anyway?

Re: init.rc script fails because tty detach

Stuart Browne — Sun, 17 Jul 2005 06:31:13 GMT

Oh, I should probably expand on that a bit further.

Some applications grab STDIN, STDOUT and STDERR rather firmly when they start, even if they are backgrounded. Sometimes you need to force thse file-descripters to go elsewhere, i.e.:

nohup processname < /dev/null > /dev/null 2>&1 &

But tell us what you're trying to background like this in the RC scripts, and we'll see if there's a better way.

Re: init.rc script fails because tty detach

Devender Khatana — Sun, 17 Jul 2005 08:18:50 GMT

Hi,

Could delaying the script for sometime will help ? I would thought of giving it a try. Delay the script for atleast 10-20 secs for it to start before proceding to execute the next script.

But can not it be done by putting it somewhere in /sbin/init.d and link to required runlevel as Sudeesh mentioned. A brief desciption of what you are trying to achive will help us a bit to help you better.

HTH,
Devender

Re: init.rc script fails because tty detach

Eknath — Sun, 17 Jul 2005 22:06:29 GMT

Hi Manoj,

As Sudeesh suggested the best way would be to try the script once the system is booted. If the script works fine the you can use the template in /sbin/init.d to customize your script. Then based on requirement of the script place it in either rc2.d/rc3.d/...

Cheers!!!
eknath

Re: init.rc script fails because tty detach

manoj_pu — Mon, 18 Jul 2005 11:26:40 GMT

I am trying to start xvfb (xserver) and mwm xserver manager by using init.rc in the system startup.

Same startup script works fine if I run manually.

startup script - /sbin/init.d/xvfb
and it is link to /sbin/rc3.d/S995xvfb

Now the problem is:
When system starts script starts xvfb and mwm, below is the process details

â root 4886 1 0 22:31:14 console 0:03 /usr/bin/X11/X :10 -ac -fbdir /var/X11/Xserverâ

â root 4890 1 0 22:31:44 console 0:00 /usr/bin/X11/mwm -display :10â

This process status remain same untill the system console login prompt comes.

After that xvfb remain running with below process status and mwm process automatically dies.

root 4886 1 0 22:31:14 ? 0:03 /usr/bin/X11/X :10 -ac -fbdir /var/X11/Xserver

Please tell me how to "demonize" the mwm process and then detach it from the console as what is happening with xvfb automatically.

Thanks and Regards

Manoj

Re: init.rc script fails because tty detach

manoj_pu — Mon, 18 Jul 2005 11:35:17 GMT

Just repeating

xvfb & mwm process status

before system console login prompt comes

root 4886 1 0 22:31:14 console 0:03 /usr/bin/X11/X :10 -ac -fbdir /var/X11/Xserver

root 4890 1 0 22:31:44 console 0:00 /usr/bin/X11/mwm -display :10

After system console login prompt comes
only xvfb survive and mwm dies

root 4886 1 0 22:31:14 ? 0:03 /usr/bin/X11/X :10 -ac -fbdir /var/X11/Xserver

Regards

Manoj

Re: init.rc script fails because tty detach

Mel Burslan — Mon, 18 Jul 2005 12:30:31 GMT

Manoj,

I am under the impression that you have not tried the nohup option yet. Did you ?

in your startup script, make sure you have somthing like this :

DISPLAY=`/usr/bin/hostname`:10; export DISPLAY
nohup sh -c '/usr/bin/X11/Xvfb :10 -ac \
-fbdir /var/X11/Xserver & ; \
sleep 5; /usr/bin/X11/xhost + ; \
/usr/bin/X11/mwm &' > /dev/null

Re: init.rc script fails because tty detach

manoj_pu — Mon, 18 Jul 2005 12:58:59 GMT

Burslan,

You are exactly right.

But that does not work to "demonize" the mwm process in the system startup.

Do you have any other catch on it???

Re: init.rc script fails because tty detach

Mel Burslan — Mon, 18 Jul 2005 13:52:26 GMT

To the best that I know daemons are written, compiled and linked to be daemons. You can not just expect any executable to be run as a daemon in the full meaning of it. nohup and running it in the background as a detached process is the best thing you can do without re-writing the whole program yourself.

Some programs have the option of running themselves ad daemons, like sendmail, with proper command switches but a quick glance over mwm does not show anything close to this.

Also, running a process in the background, doing whatever you are expecting from it to do, is not much different than the actual daemon functionality, maybe with a bit of extra overhead due to shell handling etc. What else are you after by runnig it as a *true* daemon ?

Re: init.rc script fails because tty detach

A. Clay Stephenson — Mon, 18 Jul 2005 16:19:22 GMT

If you must daemonize a process using a scripting language then Perl is your best bet. It lets you use setsid() to detach the process from a controlling terminal. Try the attached Perl script and make your changes in the "exec" function. The idea is that the process forks() then the parent is allowed to exit; the child then sets up any signal handlers and does an exec(). It's also a good idea for all daemons to to a cd to / so that umounts won't fail with "device busy".

Re: init.rc script fails because tty detach

manoj_pu — Tue, 19 Jul 2005 07:28:11 GMT

All,

Finally the the story end successfully!!!
Special thanks to Stephenson for wonderful perl script.

Thanks & Best Regards

Manoj