Specifications

Many tools require some storage place in a filesystem, so we must provide at least one (small)
writable filesystem. For all data which may be lost when the system goes down, a "tmpfs"
filesystem is the optimal choice. To create such a writable tmpfs filesystem we add the following lines
to the /etc/rc.sh script:
# mount TMPFS because root-fs is readonly
/bin/mount -t tmpfs -o size=2M tmpfs /tmpfs
Some tools require write permissions on some device nodes (for example, to change ownership and
permissions), or dynamically (re-) create such files (for example, /dev/log which is usually a Unix
Domain socket). The files are placed in a writable filesystem; in the root filesystem symbolic links are
used to point to their new locations:
dev/ptyp0 → /tmpfs/dev/ptyp0 dev/ttyp0 → /tmpfs/dev/ttyp0
dev/ptyp1 → /tmpfs/dev/ptyp1 dev/ttyp1 → /tmpfs/dev/ttyp1
dev/ptyp2 → /tmpfs/dev/ptyp2 dev/ttyp2 → /tmpfs/dev/ttyp2
dev/ptyp3 → /tmpfs/dev/ptyp3 dev/ttyp3 → /tmpfs/dev/ttyp3
dev/ptyp4 → /tmpfs/dev/ptyp4 dev/ttyp4 → /tmpfs/dev/ttyp4
dev/ptyp5 → /tmpfs/dev/ptyp5 dev/ttyp5 → /tmpfs/dev/ttyp5
dev/ptyp6 → /tmpfs/dev/ptyp6 dev/ttyp6 → /tmpfs/dev/ttyp6
dev/ptyp7 → /tmpfs/dev/ptyp7 dev/ttyp7 → /tmpfs/dev/ttyp7
dev/ptyp8 → /tmpfs/dev/ptyp8 dev/ttyp8 → /tmpfs/dev/ttyp8
dev/ptyp9 → /tmpfs/dev/ptyp9 dev/ttyp9 → /tmpfs/dev/ttyp9
dev/ptypa → /tmpfs/dev/ptypa dev/ttypa → /tmpfs/dev/ttypa
dev/ptypb → /tmpfs/dev/ptypb dev/ttypb → /tmpfs/dev/ttypb
dev/ptypc → /tmpfs/dev/ptypc dev/ttypc → /tmpfs/dev/ttypc
dev/ptypd → /tmpfs/dev/ptypd dev/ttypd → /tmpfs/dev/ttypd
dev/ptype → /tmpfs/dev/ptype dev/ttype → /tmpfs/dev/ttype
dev/ptypf → /tmpfs/dev/ptypf dev/ttypf → /tmpfs/dev/ttypf
tmp → /tmpfs/tmp var → /tmpfs/var
dev/log → /var/log/log
In case you use dhclient also:
etc/dhclient.conf → /tmpfs/var/lib/dhclient.conf etc/resolv.conf → /tmpfs/var/lib/resolv.conf
To place the corresponding directories and device files in the tmpfs file system, the following code
is added to the /etc/rc.sh script:
mkdir -p /tmpfs/tmp /tmpfs/dev \
/tmpfs/var/lib/dhcp /tmpfs/var/lock /tmpfs/var/run
while read name minor
do
mknod /tmpfs/dev/ptyp$name c 2 $minor
mknod /tmpfs/dev/ttyp$name c 3 $minor
done <<__EOD__
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9.5.3. Root File System on a cramfs File System 117