Recently I was lucky to come across one of Transcends WiFi enabled SD memory cards. Why lucky? Because they recently turned out to be somewhat hackable. There are some recipes on the net on how to get onto the embedded system; I expect some free and alternative firmware to become available soon (but I do not know anything, just estimating!).

What is it about

Transcend produces SD memory cards with a special feature: Wireless network connections. Meaning: Within the size of an average SD card, there is not only 32 GB of flash memory but also an embeded system (which is running some linux) and a wireless network module. All within a normal-sized SD card. Original purpose is equipping a camera with this card to access taken pictures even faster. There exist some applications for iOS or Android devices to use them as a quick preview. For lame PC users (such as myself), there is a somewhat (sorry, there is no friendly synonym) crappy web interface. I would really like to use the thing from my computer without any crappy "app" or http interface. I would prefer a classic network protocol originally designed for file tansfer (yeah, I know, HTTP ... but no). Say, NFS, SMB/CIFS, or (if nothing else is available) FTP. Please don't get me wrong, I am curious and all that stuff, but I do not need to have shell access. Though it would be cool.
Some googling later, I found a very elegant way of invoking a telnet server on that embedded system in the mikrocontroller.net forums (link on the bottom). Three minutes later, I telnetted into my SD card (a somewhat interesting feeling to have a shell on something small enough to swallow it). And some tests later, there was my FTP server.
The way was so easy, I just had to write this article. Here is the howto: Take the SD. Put it into a SD card reader and mount the file system. Then, create a file named autorun.sh in the root directory of the card and drop the following lines into it:
telnetd -l  /bin/sh &
tcpsvd -E 0.0.0.0 21 ftpd -w /mnt/sd/ &
The file is processed on startup and there should be a telnet and a ftp server running.
Caution: There is no login procedure to both, meaning the WPA key of the card (when in AP mode) is the only thing preventing other people from accessing both the system using telnet and the files using ftp.

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