[ale] screen -d -m

[James Sumners]

You may also want to name your screen sessions so it will be easier to
reattach to them. You can use the 'S' switch for that. E.g. `screen
-dmS session_1 some_program -with -options` where "session_1" is the
name of the session and "some_program" is the program you wish to run.

I use screen as a sort of daemon for some programs. You might want to
check out my Unreal Tournament 2004 dedicated server script. It is
available on my "code" page on my website (see signature). It is isn't
too impressive but it uses this "trick" and another to make sure a
process is constantly running.

On 4/12/06, Dow Hurst <Dow.Hurst at mindspring.com> wrote:
> I found a nice trick.  I wanted to run a python program called Modeller
> that generates protein structures from templates.  Not important to
> y'all, but the point is that it is a program that somewhere was starting
> something that wouldn't go into the background.  I was trying to start
> multiple instances across a cluster using a script.  Each node needed
> two ssh commands to start two instances of Modeller.  This true
> embarrassing parallellism at it's best!
>
> My example:
>
> #!/bin/bash
> CWD=`pwd`
> ssh node001a "cd $CWD/01;mod8v2 01_vary_loop.py &"
> ssh node001a "cd $CWD/02;mod8v2 02_vary_loop.py &"
> ssh node002a "cd $CWD/03;mod8v2 03_vary_loop.py &"
>
> and so on up to 40.
>
> Well, the first ssh statement would not go into the background with a
> "&" at the end, or a "2>&1 ./log &" at the end.  I tried regular
> expression tricks like \& and such but finally realized that some part
> of the python process was holding on the the terminal and ssh would not
> complete and return.  I hope my explanation makes sense here!  Anyway, I
> found that using screen -d -m would start a virtual terminal for ssh to
> run in and allow Modeller to run to completion while my script started
> other instances.
>
> So I ended up with this, which works:
>
> #!/bin/bash
> CWD=`pwd`
> screen -d -m ssh node001a "cd $CWD/01;mod8v2 01_vary_loop.py"
> screen -d -m ssh node001a "cd $CWD/02;mod8v2 02_vary_loop.py"
> screen -d -m ssh node002a "cd $CWD/03;mod8v2 03_vary_loop.py"
>
> I thought this was a neat solution for my problem and wanted to share
> it.  By the way, the cluster here has ssh setup so no password is
> required and that is how the script can run without problems.  I'm sure
> there is a much better way to do this with the installed Torque and Maui
> but I haven't figured out the job templates to start using them yet.
> I'm still building my own stuff like this or using mpirun for the
> parallel enabled programs.  Modeller is not parallelized so most people
> use a single random number seed and run one instance of the program for
> a long time to generate lots of possible protein structure conformations
> for their target.  I wanted to turn around the job faster so use a
> different random number for each instance of Modeller I run and then use
> the whole cluster to run 40 instances of Modeller.  I got 1000
> structures in 1 hour rather than taking a couple of days on 1 CPU.  I
> just hadn't realized screen could spawn a command in the background
> pre-detached and then exit when finished.
> Thanks,
> Dow
>
>
>
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>


--
James Sumners
http://james.roomfullofmirrors.com/

"All governments suffer a recurring problem: Power attracts
pathological personalities. It is not that power corrupts but that it
is magnetic to the corruptible. Such people have a tendency to become
drunk on violence, a condition to which they are quickly addicted."

Missionaria Protectiva, Text QIV (decto)
CH:D 59