Linux boot with NO writes?

On Tue, 2003-11-04 at 16:12, Alan Dayley wrote:
> Is it possible to boot Linux without writing to media?
>
> Let me explain. Knoppix and the like boot from a CD but they create a
> RAM drive to write the boot log and other information. What if I didn't
> want to make a boot log for whatever reason? Like, the RAM size was
> limited and I didn't want to use it up with log data.
>
> Another way to ask it is: Can the log and ALL other writes at boot time
> be piped to /dev/null? I assume in would be a pain simply because each
> service started in the boot would have to be redirected or have the log
> disabled.
>
just don't use syslog...don't have it in your startup scripts, don't run
it. The boot messages by the kernel are put into a circular buffer
(though it acts like a limited FIFO), retrieved by utilities like dmesg.
This is how I do it. I don't know the "why" it works..i assume syslog()
calls are just ignored and the applications don't care.

The only worry is that some applications _need_ a place to put their PID
and other volatile data. Some applications don't care, some whine and
refuse to go on until they have a place to put them. Apache is one of
them..the startup scripts given out by apache require /var/run or
/var/log ....i solve this with in my boards by recommending our
customers create a tmpfs ramdisk, and lay that over /var. TMPFS is nice
in that you can specify the upper-limit of memory it will grab, and i
believe it can shrink itself according to how many pages it needs. The
upside with tmpfs is that you don't need to mke2fs it...the downside is
that if you want a /var directory structure, you need to blow-up a
tarball on top of the mounted tmpfs ramdisk.


> In answering the question, it would be safe to assume that this is a
> specialized environment, like an embedded application.
>
> Alan
>
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