The root filesystem should generally be small, since
it contains very critical files and a small, infrequently
modified filesystem has a better chance of not getting corrupted.
A corrupted root filesystem will generally mean that the system
becomes unbootable except with special measures (e.g., from a
floppy), so you don't want to risk it.
The root directory generally doesn't contain any files, except
perhaps on older systems where the standard boot image for the system,
usually called /vmlinuz
was kept there. (Most
distributions have moved those files the the
/boot directory. Otherwise, all files are kept
in subdirectories under the root filesystem:
/bin
Commands needed during bootup
that might be used by normal users (probably after
bootup).
/sbin
Like /bin, but the
commands are not intended for normal users, although they
may use them if necessary and allowed.
/sbin is not usually in the default
path of normal users, but will be in root's default
path.
/etc
Configuration files specific to the
machine.
/root
The home directory for user root. This is
usually not accessible to other users on the
system
/lib
Shared libraries needed by the programs on
the root filesystem.
/lib/modules
Loadable kernel modules, especially those
that are needed to boot the system when recovering from
disasters (e.g., network and filesystem
drivers).
/dev
Device files. These are special files that
help the user interface with the various devices on the system.
/tmp
Temporary files. As the name suggests,
programs running often store temporary files in here.
/boot
Files used by the bootstrap loader,
e.g., LILO or GRUB. Kernel images are often kept here instead
of in the root directory. If there are many kernel
images, the directory can easily grow rather big, and it
might be better to keep it in a separate filesystem.
Another reason would be to make sure the kernel
images are within the first 1024 cylinders of an IDE
disk. This 1024 cylinder limit is no longer true in
most cases. With modern BIOSes and later versions of LILO
(the LInux LOader) the 1024 cylinder limit can be passed
with logical block addressing (LBA). See the
lilo manual page for more details.
/mnt
Mount point for temporary mounts by
the system administrator. Programs aren't supposed to mount
on /mnt automatically.
/mnt might be divided into
subdirectories (e.g., /mnt/dosa might
be the floppy drive using an MS-DOS filesystem, and
/mnt/exta might be the same
with an ext2 filesystem).
/proc,
/usr,
/var,
/home
Mount points for the other filesystems. Although
/proc does not reside on any disk in reality
it is still mentioned here. See the section about
/proc later in the chapter.
