The more packages you install on your OpenWRT, the more space you need. If your router has an USB port, here is a simple way to replace the JFFS flash partition with an external USB stick or hard drive.


Install packages

First, install needed modules and a few programs.

~$ opkg install kmod-scsi-core kmod-usb-core kmod-usb2 kmod-usb-storage
~$ opkg install cfdisk e2fsprogs swap-utils

Plug your USB key and check kernel messages. It should give you the path to your USB drive.

~$ dmesg
usb.c: USB disconnect on device 01:03.2-2 address 2
hub.c: new USB device 01:03.2-1, assigned address 3
scsi1 : SCSI emulation for USB Mass Storage devices
Vendor: VBTM Model: Store 'n' Go Rev: 1.04
Type: Direct-Access ANSI SCSI revision: 02
Attached scsi removable disk sdb at scsi1, channel 0, id 0, lun 0
SCSI device sdb: 1001472 512-byte hdwr sectors (513 MB)
sdb: Write Protect is off
/dev/scsi/host1/bus0/target0/lun0: p1 p2 p3
WARNING: USB Mass Storage data integrity not assured
USB Mass Storage device found at 3

Prepare USB device

Now partition & format your usb stick as follows.

~$ cfdisk /dev/scsi/host1/bus0/target0/lun0/disc
cfdisk (util-linux-ng

Disk Drive: /dev/scsi/host1/bus0/target0/lun0/disc
Size: 512753664 bytes, 512 MB
Heads: 16 Sectors per Track: 62 Cylinders: 1009

NameFlags Part Type FS Type [Label] Size (MB)
disc1 Primary Linux ext3 [storage] 463.21
disc2 Primary Linux swap / Solaris 49.27

Format the first linux ext3 partition.

~$ mke2fs -j /dev/scsi/host1/bus0/target0/lun0/part1
mke2fs 1.40.11 (17-June-2008)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
113344 inodes, 452320 blocks
22616 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=67633152
56 block groups
8192 blocks per group, 8192 fragments per group
2024 inodes per group
Superblock backups stored on blocks:
8193, 24577, 40961, 57345, 73729, 204801, 221185, 401409
Writing inode tables: done
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 20 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.

And mount it

~$ mkdir -p /mnt/root
~$ mount /dev/discs/disc0/part1 /mnt/root

We may also need some swap just in case the router runs out of memory

~$ mkswap /dev/discs/disc0/part2
~$ swapon /dev/discs/disc0/part2

Copy all fs into new mounted partition.

~$ tar cvO -C / bin/ etc/ root/ lib/ sbin/ usr/ www/ var/ | tar x -C /mnt/root
~$ mkdir -p /mnt/root/tmp && mkdir -p /mnt/root/dev && mkdir -p /mnt/root/proc && mkdir -p /mnt/root/jffs && mkdir -p /mnt/root/mnt/openwrt && mkdir -p /mnt/root/sys

Use the new partition as root partition

Here comes the interesting part. Create a new script in init.d to mount the usb drive at startup.

~$ cat > /etc/init.d/mountusb << EOF
#!/bin/sh /etc/rc.common


start () {
echo "loading USB and ext3 modules"

for module in usbcore usb-ohci uhci ehci-hcd scsi_mod sd_mod usb-storage jbd ext3; do
insmod $module
sleep 2s

[ "$FAILSAFE" != "true" ] && [ -b $EXTERNAL_PARTITION ] && {
mount $EXTERNAL_PARTITION /mnt/root
[ -x /mnt/root/sbin/init ] && {
mount -o move /proc /mnt/root/proc && \
pivot_root /mnt/root /mnt/root/mnt/openwrt && {
mount -o move /mnt/openwrt/dev /dev
mount -o move /mnt/openwrt/tmp /tmp
~$ chmod +x /etc/init.d/mountusb
~$ cd /etc/rc.d/ && ln -s ../init.d/mountusb S06mountusb

This script uses pivot_root to make /mnt/root the new / and will move the current root folder to /mnt/root/mnt/openwrt. The other mount commands will make sure the /proc, /dev & /tmp are updated.

Now reboot your router "et voilà"! You're ready to fill all this space with new packages & stuff.



# Which version/build/revision of openwrt you are usbarshad 2011-06-17 18:28
Your guide is nice, but i stuck at ~$ cfdisk /dev/scsi/host1/bus0/target0/lun0/disc
I cannot see scsi in /dev/

can you please help ?
# Guest 2011-06-17 18:40
Hi, I\'m running Kamikaze 8.09.2 (r18961). What\'s the output of dmesg when you plug your usb drive?
# device is probably differentCatfish 2011-07-02 05:50
i have found my device is usually something like /dev/sda and not the long scsi device names in this guide. if you are able to already mount your usb device manually, use the device name you use to mount it. mine is /dev/sda1 so i mount like:

mount /dev/sda1 /mnt/root

so i would use: cfdisk /dev/sda

note to use just the device name, not the partition number when you run cfdisk (because you are working on an entire device, not a single partition).
# Trouble having this workCatfish 2011-07-02 11:14
I am trying to make my Netgear WGT634U load openwrt from the USB stick. The USB drive is /dev/sda.

I partitioned the drive so Linux ext3 is sda1 and swap sda2.

I have all the packages installed as listed above and can manually mount the drive. I cannot make it mount the swap partition.

I have followed the instructions from \"Copy all fs into new mounted partition.\" onwards but the device will not boot from the USB drive. It actually doesn\'t auto mount the device on start up. I edited /etc/config/fstab with settings to automount the drive but it doesn\'t.

I am unsure when the mountusb script runs, i assume at runtime at some point but I can\'t see any output from it in the system logs via the web interface. The only way I can see it in the log is if I add a command to run it in /etc/rc.local

Is there a way to know when this is being started or if it is running and failing?
# Guest 2011-08-24 09:12
At startup, your linux system will execute all scripts found in /etc/rc.d/S*. The mount script is usually named S20fstab which means the S06mountusb script will be executed first (the numbers after S define the order of script execution)

Replacing your root filesystem is not a common mount operation as it require a pivot_root so you won\\\'t be able to do this with a new entry in /etc/config/fstab.

The /etc/localrc script is executed at the very end of system startup so at this point it is too late to replace the root filesystem.

Few tips to track your issue:
First make sure your /etc/init.d/mountusb script has execution permission.
Then change your script so all commands get logged. For example you can change the insmod line to:
insmod $module 2&>1 >> /tmp/usbmount_log
so you\\\'ll get all messages from module loading in a log file. Do the same for all mount commands in the script.

Hope this helps.
# mountusb script is not running or is exiting earlyCatfish 2011-08-20 09:59
Hi there,

I added the logging commands like you suggested, but /tmp/mountusb_log is not even being created.

/etc/init.d/mountusb is definitely executable. My only question is, are we talking about /etc/init.d/ in the root filesystem before the reboot or the root filesystem we create in the guide? (ie: /mnt/root/etc/init.d)

I added some lines to echo a message that we are trying to mount the filesystems but these messages do not show up in the startup messages either. therefore, either mountusb is not running or is exiting before it gets to those lines to echo the information.

The only lines before the echo are:
#!/bin/sh /etc/rc.common


start() {
echo \"loading USB and ext3 modules\"

# re: mountusb script is not running or is exiting eGuest 2011-08-24 09:36

/etc/init.d/mountusb is definitely executable. My only question is, are we talking about /etc/init.d/ in the root filesystem before the reboot or the root filesystem we create in the guide? (ie: /mnt/root/etc/init.d)

When booting your system looks for scripts in /etc/rc.d/. You should have a symlink /etc/rc.d/S06mountusb pointing to /etc/init.d/mountusb.

When running the pivot_root command the /etc/rc.d will be replaced by the one in /mnt/root/etc/rc.d/.

This implies all scripts running *after* S06mountusb will be read from /mnt/root/etc/rc.d/. If you want to change a script being executed prior to S06 you have to do it in /etc/rc.d/. If you want to change a script executed after S06 (let\'s say S20fstab) you have to edit the script in /mnt/root/etc/rc.d/.

There\'s no reason this script can\'t be executed. Please double check your permissions & symlink.
I\'m seeing a space in \"START =06\", I hope it\'s a typo in your message (would cause an error in shell script).
You may also read other script in /etc/init.d. My OpenWRT version (Kamikaze 8.09.2 r18961) uses \"START=06\" to define the order of script execution but things may be differents with other versions.
# order of scriptsMrTea 2012-01-08 22:00
neo73 & guys here thanks for this guide & infos

in my case (Backfire) had to modify the script \"START\" & rc.d file to get it to start at a later phase through the inits after the usb was ready ... then all worked very well plenty of new flash space to install new apps packages !

# Ta! 2012-03-15 20:18
Thank you!
This is one of the best written tutorials if have sseen in a while! You Realy saved my day.
# Mistake?Saurabh 2013-09-01 15:03
Will this work on the current versions of openWRT?
BTW, is this
opkg cfdisk e2fsprogs swap-utils

opkg install cfdisk e2fsprogs swap-utils
# Thanksneo73 2013-12-01 13:18
Thank you for pointing out this mistake!
This method should still work on newer versions of OpenWRT. You can also check alternative ways to mount rootfs on external storage at