OpenWRT install to RAM – run iftop on a router with very limited flash

November 23rd, 2018 by

OpenWRT is awesome, as it allows you to run proper Linux tools on your home router. I’m currently using a very old, underspecced TP Link box, with 32MB of RAM, but just 4MB of flash storage. This is just enough to get what I need installed, but one thing I’ve always wanted to do is use iftop to quickly see what’s using all the bandwidth. Unfortunately iftop, with its dependencies on libpcap and libncurses, just won’t fit into a 4MB image.

I recently stumbled across opkg’s install-to-RAM option, allowing me to use the 32MB of RAM to install the package, with the minor and obvious downside that it gets uninstalled when the router gets rebooted. For something like iftop, which is used for ad-hoc diagnostics, this isn’t a big issue.

Installing to RAM puts the packages under /tmp, so a little effort is required to make sure that libraries and other resources can be found. I now have the following shell script which installs iftop if it isn’t already, sets some environment variables and invokes iftop:

#!/bin/sh

if [ ! -f /tmp/usr/bin/iftop ] ; then
  opkg update
  opkg install -d ram iftop
fi

export LD_LIBRARY_PATH=/tmp/usr/lib
export TERM=xterm
export TERMINFO=/tmp/usr/share/terminfo/

/tmp/usr/bin/iftop $@

Fortunately I do have enough free space on flash storage to store the above script.
Obviously a similar approach could be used with other packages that are only needed “on demand”.

Posted in Misc, Staff Projects