RO root file system - Embedded

This is a discussion on RO root file system - Embedded ; hello group, I have a simple issue. I am currently developing an embedded linux system, based on the following hardware characteristics: via eden 800mhz(aka i586) 256 mb EmbedDisk 128 mb ram The system that i am going to build must ...

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Thread: RO root file system

  1. RO root file system

    hello group,

    I have a simple issue. I am currently developing an embedded linux
    system, based on the following hardware characteristics:

    via eden 800mhz(aka i586)
    256 mb EmbedDisk
    128 mb ram

    The system that i am going to build must hold this:

    - sshd
    - snmpd
    - an application

    Beside all that, I am seriously thinking of keeping a read-only root
    filesystem. I created a minimal system, which features an ext2
    filesystem, mounted rw, and everyting works just fine. If i try to
    leave the rootfs mounted ro, then sshd will not allow any logins, if i
    don't instruct it NOT to allocate a pty on login. This is a solution,
    i admit it, but an inelegant one, IMHO.

    Now, here come the questions:
    1. Of the possible ways all that can be done I thought of:

    a. partitioning the disk in more partitions, keeping / ro, and /
    dev,/tmp and /home rw, in a separate partition each one (cannot find a
    good reason to discard this option)
    b. use udev to create a dynamic /dev structure, and use tmpfs for /
    tmp and /var (and just assume that /home will be ro, for simplicity)
    (maybe the memory footprint of all that will be too large)

    I like much more b, but is it feasible? would it be an option on a 64
    mb ram system? Which one do you think to be the more appropriate way?

    2. Which filesystem should i use for the read only root filesystem?
    RomFS? SquashFS? CRAMFS?

    3. I am quite sure that the EmbedDisk is some kind of flash disk, like
    CF cards. If this is the case,
    should i use journalling fs or the ordinary ext2?

    I do not have too much experience building embedded systems, I like it
    and would like to learn new techniques. Saying so, i am looking
    forward to any comments.

    Thank you,
    Vasilis.


  2. Re: RO root file system

    Vasilis wrote:

    > 3. I am quite sure that the EmbedDisk is some kind of flash disk, like
    > CF cards. If this is the case,
    > should i use journalling fs or the ordinary ext2?


    I'd stay clear of journaled filesystems. Each write ends up as at least
    3 writes - write the change to the journal, read the journal and do the
    file change, update the journal entry as done.


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