This howto describes the process of installing and using packages on external media as well as the internal media. I used this information to install packages on my SD card. There is another howto that makes everything run from the external media: http://wiki.openwrt.org/OpenWrtDocs/KamikazeConfiguration/PackagesOnExternalMediaHowTo

I used this technique for my SD card mod. However, I assume that the same (or similar) can be used for just about any external media, but I have not tried.

For USB-capable routers, a wide array of flash and hard-disc options are available. Each has advantages and disadvantages; a hard disc holds more and can be used to provide a swap partition, while a flash device (or a flash card and reader) is small, silent and has no moving parts. Flash is quick to read but slow to write, not subject to mechanical failure but subject to wear and failure if the same pages are written more than 10000-1000000 times. If working with modified hardware, a flash tag (capacities currently of up to 16Gb) could easily be concealed within the router enclosure with nothing visible externally; for instance, there is a second USB port on the WRTSL54GS which is missing only the 4-pin connector and could serve this purpose well.

While this step may not be needed, I preferred to have an ext2 file system to better support various links and other *nix specific features.

To format the media I installed the e2fsprogs package from the White Russian's backports repository. How to use the backports repository see Packages.

ipkg install e2fsprogs

Once installed you can format the target partition like this

mkfs.ext2 /dev/mmc/disc0/part1

Replace '/dev/mmc/disc0/part1' with the device that you want to format.

Once the drive is formatted the kernel module needs to be installed and loaded for the partition to be used. Install and load the kmod-ext2 package with the following commands

ipkg install kmod-ext2
insmod ext2

To load the Ext2 module automatically on every boot

echo 'ext2' > /etc/modules.d/30-ext2

When mounting a mount-point is needed. A mount-point is the folder where the device will be attached. Once mounted the device will appear to e inside this folder. A typical place to put these points is in the /mnt folder. Since I am using this for my SD card my mount point is /mnt/sd. Create the mount point for your installation like this:

mkdir -p /mnt/sd

To make mounting in the future easier it is best to create an entry in the /etc/fstab file. Since the file is not in the default install of OpenWrt you will probably have to create it. Add the following line to /etc/fstab.

/dev/mmc/disc0/part1 /mnt/sd ext2 defaults 0 0

Replace '/dev/mmc/disc0/part1' with the device that you want to mount and '/mnt/sd' with the mount-point you made above.

Mount the drive using the following command:

mount /dev/mmc/disc0/part1 /mnt/sd

To mount the drive automatically on boot, we create a start script (in /etc/init.d) and a link that executes this script. You can use the following commands:

echo 'mount /dev/mmc/disc0/part1 /mnt/sd' > /etc/init.d/externalmount
chmod +x /etc/init.d/externalmount
ln -s /etc/init.d/externalmount /etc/rc.d/S60externalmount

To install packages to the external drive, add the following line in /etc/ipkg.conf

dest sd /mnt/sd

Where the syntax of the above line is "dest [name of destination] [destination]". The "name of destination" can be anything you want, I chose "sd" as I am using the SD card.

If using the Optware packages, the device should be mounted as /opt as the supplied ipkg-opt script already is coded to look in /opt/etc/ipkg.conf for configuration and download packages to /opt by default.

In the file /etc/profile, modify the line that reads

export PATH=/bin:/sbin:/usr/bin:/usr/sbin

to read

export PATH=/bin:/sbin:/usr/bin:/usr/sbin:/mnt/sd/bin:/mnt/sd/sbin:/mnt/sd/usr/bin:/mnt/sd/usr/sbin

Note: as with everything else in this howto you must replace /mnt/sd with YOUR mount-point.

Also in /etc/profile, add the following line:

export LD_LIBRARY_PATH=/lib:/usr/lib:/mnt/sd/lib:/mnt/sd/usr/lib

To install packages to the external drive use the -d option and specify the destination name that you created earlier. An example of the command for my setup is

ipkg -d sd install tcpdump

To use the packages just execute them as if they were installed on the local drive. In the "Modifying Your Environment" section of this guide you set the needed variables to allow the system to recognize programs installed on the external drive.