On Sunday 18 January 2009 17:30, Micha Feigin wrote: > I'm trying to setup a server that export root over a read only nfs file > system. I managed to enable local settings for each machine by mounting > it's own disk and then linking some files from etc. > > The only problem I'm running into is var which should be partially from the > head node (looks like most of var/lib) and some local (var/run it seems). > How do I setup var to play nicely with a readonly root file system (it is > possible to symlink what needs to be write enabled to the local disk if > needed)
I've used unionfs for this -- it's a scheme that lets you mount a read-only file system and a read-write "overlay", with copy-on-write semantics, which is to say, when you write a file, it creates a new copy of the file on the rw filesystem, and uses that in the future. It's mainly used for overlaying RAMFS filesystems over CD-ROMs on various LiveCD distros, but it also works for rw local disk over ro NFS. It's fairly straightforward to mount, and fstab understands it. It's provided by a kernel module, but the modules are packaged for Debian "etch", and I think the functionality is included in the kernel source itself for 2.6.24 (etchnhalf) and 2.6.26 (lenny), but I'm not 100% sure of that -- the machines I do this for are still vanilla "etch", so as I say, I'm not sure of the etchnhalf or lenny status. My limited experience (I inherited this configuration from the previous sysadmin) is that you definitely need to write to parts of "var" (/var/run, /var/tmp, and of course /var/log, but possibly elsewhere), you may need to write to parts of /etc (the famous /etc/udev/rules.d/z25_persistent-net.rules), and if you run a graphical desktop, it might want to put lock-files in /media when it mounts CDs and things. And there's /tmp, of course, which however might be a separate filesystem. The configuration I'm maintaining uses two unionfs overlays, one for /var and one for /etc, a small ramfs for /media, and a separate filesystem for /tmp. <http://www.filesystems.org/project-unionfs.html> <http://packages.debian.org/search?keywords=unionfs&searchon=names&version=all&release=all> <http://en.wikipedia.org/wiki/UnionFS> -- A. -- Andrew Reid / rei...@bellatlantic.net -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
