On Thu, Dec 2, 2010 at 3:53 PM, Harry Putnam <rea...@newsguy.com> wrote: > Can anyone tell me how determine what these kind of useless names > really mean? > > From df -h > Filesystem Size Used Avail Use% Mounted on > rootfs 1.9G 283M 1.6G 15% / > /dev/root 1.9G 283M 1.6G 15% / > > How are you supposed to tell what actual device these things are on. > > I know I can look in fstab... but that is something of a crap shoot > since it is user configured.
And I think in this case it is related to the linux boot process, where fstab doesn't even come into play yet anyway. In fact that's probably the reason for the "makebelieve baloney" names, I would guess (more on that later). :) > So what commands will show real devices not makebelieve baloney, and > allow me to see the usage devices are put to? In addition to what others suggested (ls or readlink), you can use stat, or you can look early-on in dmesg, for example mine shows this: [ 7.139281] EXT4-fs (sda2): mounted filesystem with ordered data mode. Opts: (null) [ 7.153529] VFS: Mounted root (ext4 filesystem) readonly on device 8:2. which seems pretty conclusive. In the case of rootfs and /dev/root you can also probably just look at your kernel commandline: $ cat /proc/cmdline root=/dev/sda2 doscsi raid=noautodetect rootfstype=ext4 video=uvesafb:1280x720p-59,mtrr:2,ywrap Which shows my root device as /dev/sda2 which matches what dmesg and ls and readlink and stat tell me. If your root is a device-mapper array or you're booting on a diskless machine over the network or other more "exotic" configurations maybe this info might not be so straightforward. In my case I have a normal PC with a non-raid boot/root drive so it's easy. > Why do we use these kind of names anyway? Kernel documentation sheds some light on it. Check out /usr/src/linux/Documentation/filesystems/ramfs-rootfs-initramfs.txt in particular. The most relevant snippet from my brief perusal: [snip] What is rootfs? --------------- Rootfs is a special instance of ramfs (or tmpfs, if that's enabled), which is always present in 2.6 systems. You can't unmount rootfs for approximately the same reason you can't kill the init process; rather than having special code to check for and handle an empty list, it's smaller and simpler for the kernel to just make sure certain lists can't become empty. Most systems just mount another filesystem over rootfs and ignore it. The amount of space an empty instance of ramfs takes up is tiny. [/snip]
