Here I’m going to share my experience with OpenWrt extroot on a TP-Link MR-3220 v2.4 router.
Though I did this on a MR-3220, this guide also applies to other routers like TP-Link WR703N, MR3020, D-Link DIR-505 etc etc. Just make sure you have downloaded the correct firmware for your router.
Probably you know all about it’s hardware specifications, here is a short recap again
- AR9331-AL3A 400MHz SoC
- 32 MB DDR RAM chip
- 4 MB SPI NOR flash memory
- One 10/100M ethernet WAN port
- Four 10/100M ethernet switches
- 150Mbps b/g/n Wi-Fi
- One USB 2.0 port
Little about MR 3220 v2.4 hardware quality, I teared it apart within 1 hour of receiving, the hardware quality is average with average quality components.
Enough hardware introduction, lets start the main topic, installing OpneWrt and configuring extroot on a USB pendrive. OpwnWrt firmware installation is very easy through the web interface and openwrt extroot part is same for almost any other router too.
Which OpenWrt firmware version should I choose ?
This is one of the most important question, choosing the correct OpenWrt version is absolutely crucial. This router works perfectly with the latest OpenWrt trunk (Designated Driver), stable 15.05, 14.07 or 12.09 .
But OpenWrt is bloating day by day while limited NOR flash storage is not, the stable firmware is also bloated with LUCI web interface. The free JFFS2 space after installing OpenWrt is decreasing too. So you can’t install more than a few package with this limited space, that’s when putting extra files on a external drive is necessary.
After about 12-14 hour experiment with various OpenWrt versions, I figured out that only OpenWrt 14.07 (Barrier Breaker) or earlier versions have the right amount of free JFFS2 space to install required bare minimal minimal packages to setup an extroot.
Note: There’s another little difficult way to run latest OpenWrt on your router, then you’ve to build OpenWrt custom firmware.
Which filesystem should I use for extroot ?
Another very important question, the official OpenWrt extroot guide says that you could any UNIX-like filesystem of your choice, forget about FAT32 or NTFS. But the reality is extroot is only and only possible with ext4/ext3 or ext2 filesystem. I tested with almost every slim (I mean which equips less NOR flash space) filesystem
- minix, not supported
- HFS, not supported
- HFS+, not supported
- JFS, not supported
- XFS, not sopported
- reiserfs, not supported
There are other UNIX-like filesystems like BTRFS, LVM2 PV , UFS etc. but none of them will fit in the 288 KB free JFFS2 space, so I didn’t tested them.
So the final choice is for a router with 4MB flash, choose only OpenWrt 14.07 or earlier and ext4 as extroot filesystem.
Request to OpenWrt pro users, if you had ever setup chroot with any other filesystem except ext4/ext3/ext2, please mention.
Installing OpenWrt on TP-Link MR3220
Assuming you have a PC running a Linux distribution, this is required for flashing the firmware and
Download the OpenWrt 14.07 firmware from here .
wget -c https://downloads.openwrt.org/barrier_breaker/14.07/ar71xx/generic/openwrt-ar71xx-generic-tl-mr3220-v2-squashfs-factory.bin
WARNING: Do it at your own risk, event with great precautions there is a chance of bricking the router. If possible connect the router to an UPS before flashing it.
- Power on the router and connect a PC through a ethernet straight cable (patch cord) to one of four the LAN ports(the yellow ones).
- Open up a browser and go to this address; 192.168.0.1 to access the web interface and login. Username: admin Password: admin .
- Go to the System Tools > Firmware Upgrade choose the previously downloaded OpenWrt firmware with the Browse button and Hit the Upgrade button.
- Wait for few minutes to let the flashing complete and automatic reboot.
Installation is complete now your PC will automatically receive a different IP via DHCP.
Initial OpenWrt setup
For first time we have to use telnet to login into OpenWrt,
or if you don’t have telnet try this
busybox telnet 192.168.1.1
after login, change the password to enable ssh
now exit from the telnet session with exit command and re-login with SSH,
Installing necessary packages
At this step the router must be connected to the internet, you could use your existing DSL/cable internet for this purpose or share an existing connection from your PC. I personally did it by sharing my 3G connection with Network-Manager from my laptop.
Make sure that the router could connect to the internet
ping -c 4 184.108.40.206
opkg package repository
Install necessary packages to support USB storage device
opkg install kmod-usb-storage kmod-scsi-core block-mount
Install ext4 filesystem kernel module
opkg install kmod-fs-ext4
That’s all, check free flash space with
df -h , do not install anything more ! if you try to do so, any packages larger than 10KB will return no space left on device error.
Now load all necessary kernel modules with modprobe command
modprobe sd_mod modprobe usb-storage modprobe ext4
Or simply reboot the device with
Partitioning the USB drive
Lets partition the USB drive, another question, how much space should I use for extroot partition ? Just 100-200 MB is more than enough, I allocated a 200 MB ext4 partition for extroot, you could use more if you wish. I used Gparted for partitioning a 4 GB USB drive.
Configuring the OpenWrt extroot
After plugging the USB drive, it should show up as a storage device under the /dev directory as /dev/sda1 , /dev/sda2 etc. Simply go through the commands bellow
Mount the USB drive, change /dev/sda2 according to yours
mount /dev/sda2 /mnt
Copy data from /overlay partition to the USB drive
tar -C /overlay/ -c . -f - | tar -C /mnt/ -xf -
Un-mount the USB drive
sync && umount /dev/sda2
/etc/config/fstab to mount the USB drive as
block detect > /etc/config/fstab
Now edit the
/etc/config/fstab with vi to mount the etxt4 partition,
/overlay partition at startup,
have a look on a sample fstab configuration,
config 'global' option anon_swap '0' option anon_mount '0' option auto_swap '1' option auto_mount '1' option delay_root '5' option check_fs '0' config 'mount' option target '/overlay' option uuid '7669178c-3f77-4fb1-b421-6ec6f61be672' option enabled '1'
Set the target to /overlay, and change the option enabled line from 0 to 1 . Now enable the fstab service at startup
and check it
readlink -f /etc/rc.d/*fstab
reboot the router with the reboot command
Check if the extroot is working or not
After the reboot is complete login to the router with ssh again and check the free disk space with
df -h mount
df commnd should return a lot of free space available at rootfs, that means extroot is working fine.
opkg install e2fsprogs
I hope this simple beginner friendly tutorial will help you to start your experiment with OpenWrt. If you have any question or suggestion, just leave a comment and also don’t forget to share this with your friends 🙂 .