Instead of rm -f /bin/sh ln -s /bin/bash /bin/sh which leaves no /bin/sh for a few moments. Anything that needs /bin/sh to exist that tries to run before it's recreated will have big trouble. This is a bad habit to get into, especially when you're working with symlinks to libraries. Instead, do ln -sf /bin/bash /bin/sh and it's all done in a single command which guarantees that there isn't even a nanosecond during which there is no /bin/sh.