One can ssh into his iphone/ipad by ssh once jailbroked and installed openssh in cydia. But the shell is /bin/sh by default.
Today I tried to change the shell to /bin/bash by modifying /etc/passwd, but then I found this didn’t help.
I got nothing useful after a bit of googling.
Finally by analysis strings in pam_unix.so I found /etc/master.passwd in it. So this is the answer: modifying /etc/master.passwd changes the shell.
Enjoy bash on ios!