Hey, this router runs Linux!

(September 2020)

I was poking around the admin web pages on my Verizon router, and noticed an option to allow local telnet access on port 23. So I tried it, and it let me login with the same user/pass as the admin pages.

Connected to
Escape character is '^]'.
Username: admin
Password: ************

Wireless Broadband Router> 

Cool! First thing to do is type help, and after browsing command options I found one to start a shell,

Wireless Broadband Router> help system shell
shell   Spawn busybox shell in foreground

Returned 0
Wireless Broadband Router> system shell
Temporary setting log_level off

BusyBox v1.01 (2005.09.07-07:38+0000) Built-in shell (lash)
Enter 'help' for a list of built-in commands.

/ #

Oh, I'm right at home there. I spend most of my working days at a Linux shell prompt.

What kind of CPU is this thing running? 99% sure its going to be a 32-bit ARM of some kind. Yup,

/ # cat /proc/cpuinfo 
Processor       : ARM926EJ-Sid(wt) rev 1 (v5l)
BogoMIPS        : 1196.03
Features        : swp half thumb fastmult edsp 
CPU implementer : 0x56
CPU architecture: 5TE
CPU variant     : 0x2
CPU part        : 0x131
CPU revision    : 1
Cache type      : write-back
Cache clean     : cp15 c7 ops
Cache lockdown  : format C
Cache format    : Harvard
I size          : 16384
I assoc         : 4
I line length   : 32
I sets          : 128
D size          : 16384
D assoc         : 4
D line length   : 32
D sets          : 128

Hardware        : Feroceon-KW2
Revision        : 0000
Serial          : 0000000000000000

How much memory is available?

/ # free
              total         used         free       shared      buffers
  Mem:       122528        93436        29092            0            0
 Swap:            0            0            0
Total:       122528        93436        29092

How much flash "disk" space is available?

/ # df
Filesystem           1k-blocks      Used Available Use% Mounted on
cramfs                    2200      2200         0 100% /mnt/cramfs
modfs                      208       208         0 100% /mnt/modfs
/dev/mtdblock0           32768      7636     25132  23% /mnt/jffs2

This is very similar to the Zink hAppy printer that I spent several years working on.

Can I write files?

/ # ps > ps.txt
/ # ls -l ps.txt
-rw-r--r--    1 0        0            1497 Sep  3 00:19 ps.txt

I wonder if Go can cross-build for this architecture? It would be cool to have a graph of network traffic in a web view, updated once every few seconds. I can see the basic info I would need in ifconfig, or more directly in /sys/class/net/*/statistics/{rx_bytes,tx_bytes).

Many (perhaps most) consumer routers have been built on Linux since the late 2000s, so this tech note isn't unique or revelatory, but I still get a thrill out of poking at devices (that I didn't make) and finding a familiar environment.

"I liked it before it was cool."

From 1999 to 2008 I used a Corel NetWinder as my home router behind my cable modem. It was a neat little machine running ARM Linux, and I had fun playing with the routing and firewall rules. At one point I had it configured play a "plink" sound through the internal speaker when a packet trying to find an unsecured service would hit and get dropped.