I had a few issues with my ubuntu. After quite some time, I decided to investigate and found the following:
ls -la /bin/sh
lrwxrwxrwx 1 root root 4 2009-05-27 16:32 /bin/sh -> dash
To speed up boot time on ubuntu, which has never been an issue if you ask me, they replaced bash with dash as the default shell (sh). So now, /bin/sh is linked to /bin/dash.
They could have changed all their boot stuff to use dash instead of bash without breaking anybody's code, but hey, that would only be half the fun. Don't tell us that would be too much work, you had to convert all your scripts to be compatible with the new shell anyway. The dash [s]hell supports a subset of what bash does, apparently only POSIX-compliant stuff. So here we are again, I'm getting "-sh: typeset: not found", let and $RANDOM that do not work anymore among many things.
Read here for more info: https://wiki.ubuntu.com/DashAsBinSh
