Install with root filesystem on Compact Flash

[Bob Chiodini]

Tim wrote:
> On Mon, 2007-07-09 at 16:57 -0700, John Wendel wrote:
>   
>> I'm building a new box and I'd like to install the root filesystem on 
>> a compact flash card. Not too hard. But I want / to be read-only, to 
>> avoid premature wear out of the flash.
>>
>> It seems that I need to use a "union filesystem" that will let me 
>> mount some writable directories (/etc, /var, ???) from another
>> device. 
>>     
>
> Another avenue that you might want to explore is changing the mount
> options so that nothing is written to the drive unless you intend it.
> i.e. Ignoring updating "access times", etc.  That lets you keep things
> writable, if you'd like to do so.
>
> I don't think you can put /etc/ on another device.  But you definitely
> can mount /var/ from another location.  /var/, /usr/, and few others can
> easily be mounted from other drives just the same as they can be on
> other partitions on a hard drive.
>
>   
John,

Another alternative is using a RAMDISK (tmpfs) for those partitions that 
you deem writable.  Or, you can put the entire / partition in the 
RAMDISK (like initrd).  On one system I did a read-only CF with a tmpfs 
file system for things that changed often, but were not needed across 
reboots and minimal bootable initrd, to have a rescue image should 
something go wrong with the main CF partition.  LILO was used to choose 
which to boot.

Generally, /etc does not need to be written very often and depending on 
what your system will be used for, you can probably get away with only 
/var as writable.  If the only things in /var that are changing are the 
logs, you can always configure syslog into remote mode.

These embedded system were done several years ago and busybox was the 
saving grace to get everything to fit in 256MB CF (big at the time) or 
an 8MB initrd (for rescue).

Bob...