01 January 2011

Mounting ISO Images

So you've created a fresh ISO image and now you want to use it, verify
its contents, etc.  Whatever your purpose, it is fairly trivial to
mount the image file and access it.  The following are our host details:
        HOSTS:          tux (Linux), beastie (FreeBSD), snorkle (Solaris)
        PROMPT:         host [0]
        OSes:           CentOS 5.4 (tux)
                        FreeBSD 8.1 (beastie)
                        Solaris 10 (snorkle)
        ISO IMAGE:      sol-11-exp-201011-text-x86.iso
        USER:           root
In each example, the following steps are performed:
        0) test for and optionally create a mount point
        1) if not handled automatically by the OS, create the requisite
           loop device associated with the image file (FreeBSD, Solaris)
        2) mount the loop device to the mount point
        3) verify the loop device is attached, review the files contained
           within the image file
        4) unmount the loop device 
        5) if not handled automatically by the OS, remove the loop device
           associated with the image file (FreeBSD, Solaris) 
Starting things off, Linux allows you to mount an image file directly
without needing to first create the requisite loop device.  The mount
command will handle this for you automatically (see note 4):
        tux [0] [ ! -d /a ] && /bin/mkdir /a
        tux [1] /bin/mount -o loop -t iso9660 /tmp/sol-11-exp-201011-text-x86.iso /a
        tux [0] /bin/df -h /a
        Filesystem            Size  Used Avail Use% Mounted on
        /tmp/sol-11-exp-201011-text-x86.iso
                              479M  479M     0 100% /a
        tux [0] /bin/ls /a
        bin   dev      jack  platform  reconfigure  save              solaris.zlib  tmp
        boot  devices  mnt   proc      root         solarismisc.zlib  system
        tux [0] /bin/umount /a 
FreeBSD, like Solaris, requires a loop device be created in order to
mount the image file.  In FreeBSD 5.x and newer, 'mdconfig' is used to
create the loop device whereas in versions prior, 'vnconfig' is used.
The following uses 'mdconfig':
        beastie [0] [ ! -d /a ] && /bin/mkdir /a
        beastie [1] /sbin/mdconfig -a -t vnode -f /tmp/sol-11-exp-201011-text-x86.iso 
        md0
        beastie [0] /sbin/mount -t cd9660 /dev/md0 /a
        beastie [0] /bin/df -h /a
        Filesystem    Size    Used   Avail Capacity  Mounted on
        /dev/md0      478M    478M      0B   100%    /a
        beastie [0] /bin/ls /a
        .catalog                dev                     root
        .cdrom                  devices                 save
        .image_info             jack                    solaris.zlib
        .livecd-cdrom-content   mnt                     solarismisc.zlib
        .volsetid               platform                system
        bin                     proc                    tmp
        boot                    reconfigure
        beastie [0] /sbin/umount /a
        beastie [0] /sbin/mdconfig -d -u 0
In the final command above, '-u 0' informs 'mdconfig' which 'md' device
to work on (md0).  Finally, in Solaris the process is much like that
in FreeBSD.  In this case, 'lofiadm' is used to create the loop device:
        snorkle [0] [ ! -d /a ] && /usr/bin/mkdir /a
        snorkle [0] /usr/sbin/lofiadm -a /tmp/sol-11-exp-201011-text-x86.iso
        /dev/lofi/1
        snorkle [0] /usr/sbin/mount -F hsfs -o ro /dev/lofi/1 /a
        snorkle [0] /usr/sbin/df -h /a
        Filesystem             size   used  avail capacity  Mounted on
        /dev/lofi/1            478M   478M     0K   100%    /a
        snorkle [0] /usr/bin/ls /a
        bin               jack              reconfigure       solarismisc.zlib
        boot              mnt               root              system
        dev               platform          save              tmp
        devices           proc              solaris.zlib
        snorkle [0] /usr/sbin/umount /a
        snorkle [0] /usr/sbin/lofiadm -d /dev/lofi/1 
 
NOTES

1. In the above a CD image is mounted, though any FS type known to the OS
    could have been used (see mount man page).
2. While not explicitly set except in the Solaris example, the mount is
    read only since this is an ISO image (see mount man page).
3. In all three examples, we allow the OS to decide what loop device
    to use. We could control this by specifically identifying the intended
    loop device:
    - Linux, as an option to 'mount':
        mount -o loop=/dev/loop2 -t FS_TYPE /path/to/image /mount/point
    - FreeBSD, as an option to 'mdconfig':
        mdconfig -a -t MD_TYPE -f /path/to/image -u 2
    - Solaris, as an option to 'lofiadm':
        lofiadm -a /path/to/image /dev/lofi/2
4. If you should want or need to manually manage the loop device handling
    in Linux:
        tux [0] /sbin/losetup -f /tmp/sol-11-exp-201011-text-x86.iso
        tux [0] /sbin/losetup -a
        /dev/loop0: [0808]:56918026 (/tmp/sol-11-exp-201011-text-x86.iso)
        tux [0] /bin/mount -t iso9660 /dev/loop0 /a
        tux [0] /bin/umount /a
        tux [0] /sbin/losetup -d /dev/loop0
    - to specify the intended loop device to create via losetup:
        losetup /dev/loop2 /path/to/image

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