Missing loopback interface and modules, and isofs mounting [SOLVED!]

Question

In my new archlinux istallation, isofs and loopback facilities are not present and when installed by hand do not seem to work. [See FINAL SOLUTION below. Thanks for the suggestions I got].
Now, I was under the impression that such facilities should be automatically available at the end of a normal installation.
For instance, in an installation I made last fall, I can mount .iso filesystem through the loopback interface with no problems (and that even without using -t, with just 'mount image.iso /mnt/iso').  In that installation, lsmod shows the modules
  loop                  18526  2
  isofs                  32946  1
(also, a module isofs is present in /lib/modules, though I cannot find a loop module there)
and eight loopback devices are available as /dev/loop0 ... /dev/loop7
On the other hand, in the new installation no /dev/loop devices are present, and no loop and isofs modules show up either
as installed (as reported by lsmod) or at least in the libraries. Has something changed recently? Do I need to install a package that will set up my installation for loopack mounting and mounting of .iso filesystems?
INTERIM SOLUTION
I mentioned above that in my older Linux box, on an Arch Linux installed months ago but not upgraded for many weeks, I had loopback devices running and isofs and loop modules installed, and all working well by itself. Today I did an upgrade, and noticed that it came with a new kernel (3.3?), probably the same I had on the new machine. So I rebooted after that---and found the exact problem as on the new machine: /dev/loop* missing, no modules isofs or loop appearing in lsmod. So I installed by hand a loopback interface, with 'mknod /dev/loop0 b 7 0'. Then I made sure I had the isofs package installed, and installed the isofs module with modprob; this time isofs showed on lsmod, but loop didn't yet. Finally I mounted a data DVD (note that the incantation -t iso9660 is no longer necessary), and as a last thing I mounted an .iso file; both worked. Only after this did a module loop show up in lsmod.
So probably something subtle changed in the dependencies between installed packages, installed modules, and installed loopback devices, so that something is out of sync and has to be nursed manually. Better experts than I may throw
some light on this problem and hopefully fix it.
FINAL AND SATISFACTORY SOLUTION
Whatever may have happened before, the following works like a charm:
I upgrade Arch; it installs 3.3.1-1-ARCH as a kernel in /boot.
I reboot to let the new kernel "take".
No loop0,...,loop7 devices show up in /dev; no isofs or loop show up with lsmod; isofs (but no loop) present in /lib/modules
I do 'mount /dev/sr0 /iso' (NOTE: no -t iso9660' option) with a CD in the sr0 drive; the CD filesystem shows up in /iso.
   After this, isofs shows up in 'lsmod|grep isofs', but no loop device yet.
I unmount /iso and do 'mount ~tt/ markov.iso /iso' (NOTE: no -t iso9660' option); the markov filesystem shows up in /iso.
  After this, loop0,...,loop7 devices show up in /dev, and a loop module (wherever that camefrom) appears in lsmod.
In other words, everything required for isofs automounts as necessary and remains mounted until new reboot.
The '-t iso9660' option is not necessary. As noted by an other Arch post, this option may be detrimental and might have been the culprit; this is an issue I will explore on the next reboot.
Last edited by rugantino (2012-04-11 20:11:55)

Answer 1

When /etc/rc.sysinit is invoked during the bootprocess; it should automatically start a loopback interface (unless you've specifically disabled it in /etc/rc.d/network or so).
Check your logs to see if your find any related errors.