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Old 02-24-2009, 10:00 PM   #1
coffeecoffee
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Read only file systems, custom live CDs, and embedded systems


Hi

I have an application that requires a version of linux with a read only file system. The idea is that non-volatile storage (harddisk) is only used to load the OS, and it is not needed at all for operation once everything is in RAM.

Some people have suggested a live CD distribution for this task. (I would be loading the contents of the live CD on to a flash ROM, but that is not a problem.) The problem is, how can I change the contents of the live CD so that it can run my applications? Wouldn't it be better if there was a way to just install linux on the flash ROM as a normal install, and then SET the filesystem to readonly? Or are liveCDs built in a special way that facilitates the read only aspect of the software?

I suppose what I really want is:
1. user turns on pc
2. linux boots to console
3. my program is started automatically which uses directFB layer and SDL
4. no non-volatile storage access occurs after this

I don't know if it's possible to modify a liveCD to do this, so it makes more sense to install linux normally and use a readonly filesystem but I have no idea if this will break things.

I would appreciate any help! Thanks!
 
Old 02-24-2009, 10:50 PM   #2
gergely89
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When running a LiveCD like Knoppix for example, you have some virtual disk space, which is actually located in your RAM. So you can install your application neatly, Knoppix will not affect your real hard disks (unless you explicitly mount them and make them writeable and do something with them).

The drawback is that after shutdown your installed application will be gone (it existed only in memory), so the next time you launch the LiveCD you have to install your application again. Knoppix actually allows you to store some personal data or applications to a real hard disk, as to avoid repeating setups, but it doesn't do it without your authorization.

linux

Last edited by gergely89; 02-27-2009 at 11:00 PM.
 
Old 02-24-2009, 11:09 PM   #3
coffeecoffee
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That's not really what I'm looking for. What I want to know is if it's possible to install linux normally (not a livecd) and then make the filesystem readonly after I have added/removed whatever packages I require.. what I don't want is lots of linux error messages in the background about not being able to write to disk...
 
  


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