For LTSP client, a /usr/share/ltsp/init-ltsp.d script with sed yields duplicate results

[John Hupp]

I want to use a client boot script at 
/usr/share/ltsp/init-ltsp.d/50-apcupsd with sed to modify a 
configuration file for apcupsd (APC UPS manager daemon).  The script:

sed -i \
     -e 's/UPSCABLE usb/UPSCABLE ether/' \
     -e 's/UPSTYPE usb/UPSTYPE net/' \
     -e 's/DEVICE/DEVICE Lubuntu1:3551/' \
     -e 's/TIMEOUT 105/TIMEOUT 60/' \
     -e 's/NETSERVER on/NETSERVER off/' \
     -e 's/NISIP 0.0.0.0/NISIP 127.0.0.1/' \
/etc/apcupsd/apcupsd.conf

It all works fine except for this substitution:
     -e 's/DEVICE/DEVICE Lubuntu1:3551/'

It takes this line:
     DEVICE
and replaces it with this:
     DEVICE Lubuntu1:3551 Lubuntu1:3551

However, if I run the same script on the server, it does not produce the 
duplicate "Lubuntu1:3551".
-------------------------------------

Wondering if the colon was a special character that needed to be escaped 
(but not sure exactly how to do that), I tested the idea by simply 
replacing it with a space.  Effectively:

     sed -e 's/DEVICE/DEVICE Lubuntu1 3551/'

Now on the LTSP client, the resulting line is:

     DEVICE Lubuntu1:3551 Lubuntu1 3551
-------------------------------------

I don't know what the syntax means, but someone also suggested the 
following:

     sed -e 's/DEVICE$/DEVICE Lubuntu1:3551/'

And that had no effect whatsoever.  The result was still "DEVICE 
Lubuntu1:3551 Lubuntu1:3551".
-------------------------------------

Seeking a work-around, I added an /etc/apcupsd/apcupsd_slave.conf file 
which was already modified with the parameters I want clients to boot 
with.  Then I edited /usr/share/ltsp/init-ltsp.d/50-apcupsd to remove 
the sed command and added:

     cp /etc/apcupsd/apcupsd_slave.conf  /etc/apcupsd/apcupsd.conf

But this does not seem to execute.  I also tried:

     rm /etc/apcupsd/apcupsd.conf
     cp /etc/apcupsd/apcupsd_slave.conf  /etc/apcupsd/apcupsd.conf

But this does not execute either.  And if on a booted-up client I open a 
local session xterminal and run:

     $ su root cp /etc/apcupsd/apcupsd_slave.conf /etc/apcupsd/apcupsd.conf

it returns:

     /bin/cp: cannot execute binary file

[Does anyone know why?]
-------------------------------------

Someone pointed out that with my initial sed command, I would get the 
duplicate result I report if the script ran twice.  So one question 
might be whether there is some mechanism that would cause the script to 
run twice.  For instance, if LTSP is actually built such that I only 
need the /usr/share/ltsp/init-ltsp.d/50-apcupsd script on the server, 
and not in the client network boot image, that would cause it to run twice.

But I don't think that is what's going on.  My current thought is this: 
I think the LTSP clients use a static, read-only network boot image + a 
writable union filesystem overlaying the read-only image.  I have saw a 
slim mention of that in writing somewhere, sometime.  (Perhaps I'm not 
searching with the right terms to find better documentation.)  But if 
that overlay has persistence somehow, or is cached on the server, then 
perhaps there could be results like the above.  It would effectively be 
run multiple times over succeeding boots and be applied to a persistent 
overlay.

Can anyone confirm if LTSP uses something like a writable overlay 
filesystem?  If so, can I read more about that somewhere?

Does anyone have a work-around?
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