Why can't I run "adb shell"?

[AC Question]

Hi. I purchased an Android Tablet (4.0: Ice Cream Sandwich) on eBay. I'm trying to install my own custom apps, but failing. If I connect the Tablet to my Linux PC, and run a simple command, I get this result:

# adb shell
- exec '/system/bin/sh' failed: Permission denied (13) -

Without any shell, what can I do? The tablet otherwise works normally and a non-programmer probably wouldn't know anything is wrong. But I need to program apps and install them. Is my device bricked?

 

[LeoRex]

There are a few things to check... first, is USB Debugging enabled on the tablet? You will not be able to connect ADB without that enabled. Second, where is the command being executed and what are the details of that environment (have you used adb to connect to any other Android devices, etc).