13 December 2010

loop -de- loop

As I count it at the moment, I am building and using content from more than eight loop mounted ISOs on a principal NFS, TFTP and 'next', and FTP server in the internal network

Red Hat has updates for 4.9, and 5.6 in beta; CentOS is in QA on a initial '6' release; I am doing private builds for a Fortune 50 on some backports out of RawHide and from some local packaging; and I am working on a 'back of the envelope' design and test to try to get control of the huge bloat on Red Hat ISO space for installs, to see if I can get a trimmed minimal installer for i386, x86_64, ppc[64] and s390x down to a single piece of CD sized ISO media. Then there is my favorite of the minimal wire install image, again which I package up into an ISO

Going forward, we will see more of encrypted filsystems across loop devices, and that will also put load on here. It may be time for the kernel folks to consider bumping that limit to 16

As such I regularly crest over the stock eight provided loop devices. To address this without a reboot, one simply has to:

# shutdown all uses of loop devices, so we can remove the module
/sbin/rmmod loop
echo "options loop max_loop=255" > /etc/modprobe.d/loop.local.conf
/sbin/depmod -a
/sbin/modprobe loop

Note: that 'depmod' may not be strictly required, but will in any event be harmless, so I do it -- heck, I still type sync ; sync before rebooting a box, and I KNOW that is not needed any more. The force of habit ...

I add the suffix .conf on that file, because I was scolded by a Debian box a couple weeks ago on the topic; it seems that they are deprecating sourcing files in /etc/modprobe.d/ lacking such. Since when did Linux starting use file name suffixes to determine a file's content? -- at least it is not required to be in 8.3 format

Another approach is doing it with hard-coded values at boot time, with sysctl.conf or such

Tip of the hat to Paul Howarth on the SELinux rant I went off on last week; The interaction of loop mounted ISOs, and mounts in the FTP space of a filesystem can also be addressed with options to the mount command, and in the /etc/fstab with context= choices. He writes and points out:

I use context mounts to avoid it, e.g. in fstab:

   /path/to/dvd1 iso9660
   0 0

... sorry about the funky line wrapping, but there is just no good way to display really long /etc/fstab entries