Activating extroot on OpenWrt 12.09-rc1

Enabling extroot on OpenWrt 12.09-rc1 is bit tricky. Likely reason you're trying to enable extroot is lack of free space i.e. router with 4MB flash. Problem is that unless you're interested in creating custom firmware images there's no space left for tools to enable extroot using old procedure. Following has been tested with TP-Link MR3220 v1. It's ar71xx with 32MB RAM and 4MB flash being lowest end of currently supported OpenWrt compatible devices.

# Install packages to support extroot

# Since OpenWrt 12.09-rc1 included Luci it's tight fit on 4MB flash devices

# and we're forced to install required tools on-demand instead of all at once

opkg update

opkg install kmod-usb-storage fdisk

# Wipe old partition table from /dev/sda

# to wipe entire device which can take for a while drop "count=1" from end

dd if=/dev/zero of=/dev/sda bs=64k count=1

# Create new partitions, 64MB swap, 256MB root and rest as separate partition

cat <<'__EOF__' | fdisk /dev/sda

n

p

1

+64M

t

82

n

p

2

+256M

n

p

3

w

q

__EOF__

# Verify partitions, should look something like this

root@OpenWrt:/# fdisk -l /dev/sda

Disk /dev/sda: 1050 MB, 1050935296 bytes

33 heads, 61 sectors/track, 1019 cylinders, total 2052608 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk identifier: 0x2785a891

   Device Boot      Start         End      Blocks   Id  System

/dev/sda1            2048      133119       65536   82  Linux swap / Solaris

/dev/sda2          133120      657407      262144   83  Linux

/dev/sda3          657408     2052607      697600   83  Linux

# Remove fdisk to make some space for e2fsprogs

opkg remove fdisk

opkg install e2fsprogs

# Create root and data filesystems

mkfs.ext3 /dev/sda2 -L openwrt-extroot

mkfs.ext3 /dev/sda3 -L openwrt-data

# Remove e2fsprogs and install mkswap

opkg --force-removal-of-essential-packages remove e2fsprogs libext2fs libcom_err libpthread

opkg install swap-utils

# Create swap

mkswap /dev/sda1 -L openwrt-swap

# Install blkid, block-mount and ext2/ext3/ext4 driver required for extroot support

opkg install blkid block-mount kmod-fs-ext4

# Check status with blkid

root@OpenWrt:/# blkid

/dev/mtdblock2: TYPE="squashfs"

/dev/sda1: LABEL="openwrt-swap" UUID="ef9f9054-7d12-4aa3-a3ee-9a56baae91b1" TYPE="swap"

/dev/sda2: LABEL="openwrt-extroot" UUID="c1ad543d-f24b-4363-b6a8-77639010a560" SEC_TYPE="ext2" TYPE="ext3"

/dev/sda3: LABEL="openwrt-data" UUID="c6472265-be07-49db-862f-bd75cff3956e" SEC_TYPE="ext2" TYPE="ext3"

# Cleanup default fstab configs as they don't work for us

/etc/init.d/fstab stop

uci delete fstab.@swap[0]

uci delete fstab.@mount[0]

uci commit fstab

# Enable swap on next boot

uci add fstab swap

uci set fstab.@swap[-1].uuid=`blkid -s UUID /dev/sda1 | cut -d\" -f2`

uci set fstab.@swap[-1].enabled=1

uci commit fstab

# Enable extroot on next boot

uci add fstab mount

uci set fstab.@mount[-1].uuid=`blkid -s UUID /dev/sda2 | cut -d\" -f2`

uci set fstab.@mount[-1].options=rw,sync,noatime

uci set fstab.@mount[-1].fstype=ext3

uci set fstab.@mount[-1].enabled_fsck=1

uci set fstab.@mount[-1].enabled=1

uci set fstab.@mount[-1].target=/

# Enable data partition on next boot

mkdir -p /mnt/data

uci add fstab mount

uci set fstab.@mount[-1].uuid=`blkid -s UUID /dev/sda3 | cut -d\" -f2`

uci set fstab.@mount[-1].options=rw,sync,noatime

uci set fstab.@mount[-1].fstype=ext3

uci set fstab.@mount[-1].enabled_fsck=1

uci set fstab.@mount[-1].enabled=1

uci set fstab.@mount[-1].target=/mnt/data

uci commit fstab 

# Disable anon mount feature

uci set fstab.automount.anon_mount=0

uci commit fstab

# Resulting /etc/config/fstab

root@OpenWrt:~# cat /etc/config/fstab

config global 'automount'

        option from_fstab '1'

        option anon_mount '0'

config global 'autoswap'

        option from_fstab '1'

        option anon_swap '0'

config swap

        option uuid 'ef9f9054-7d12-4aa3-a3ee-9a56baae91b1'

        option enabled '1'

config mount

        option uuid 'c1ad543d-f24b-4363-b6a8-77639010a560'

        option options 'rw,sync,noatime'

        option fstype 'ext3'

        option enabled_fsck '1'

        option enabled '1'

        option target '/'

config mount

        option uuid 'c6472265-be07-49db-862f-bd75cff3956e'

        option options 'rw,sync,noatime'

        option fstype 'ext3'

        option enabled_fsck '1'

        option enabled '1'

        option target '/mnt/data'

# Populate new root with copy of current root

mkdir -p /mnt/sda2 /tmp/cproot

mount --bind / /tmp/cproot

mount /dev/sda2 /mnt/sda2

tar -C /tmp/cproot -cvf - . | tar -C /mnt/sda2 -xf -

sync

umount /mnt/sda2

umount /tmp/cproot

# Activate extroot on next boot

/etc/init.d/fstab enable

/etc/init.d/fstab start

/etc/init.d/fstab whole_root_enable

# Reboot router

reboot

# Check mounts and swap after reboot

root@OpenWrt:/# df -h

Filesystem                Size      Used Available Use% Mounted on

rootfs                  246.0M     15.3M    217.9M   7% /

/dev/root                 2.0M      2.0M         0 100% /rom

tmpfs                    14.3M     76.0K     14.2M   1% /tmp

tmpfs                   512.0K         0    512.0K   0% /dev

/dev/sda2               246.0M     15.3M    217.9M   7% /

/dev/sda3               671.3M     17.5M    619.7M   3% /mnt/data

root@OpenWrt:/# free

             total         used         free       shared      buffers

Mem:         29220        20408         8812            0         2380

-/+ buffers:              18028        11192

Swap:        65532            0        65532

# We can now install bunch of useful tools since we have plenty of space

opkg update

opkg install fdisk e2fsprogs tcpdump screen mtr wget luci-app-samba

# Have fun!