Replacing sh with zsh

Question

I have replaced sh with zsh with the following commands:

$ sudo mv /bin/sh /bin/sh1
$ sudo ln -s /usr/bin/zsh /bin/sh
$ ls -l /bin/sh
lrwxrwxrwx 1 root root 12 Jul  6 20:48 /bin/sh -> /usr/bin/zsh
$ which sh
/bin/sh
$ sh
$ exit
$ zsh
mpc% exit

As you can see, the sh command doesn't open a zsh shell although it has been linked. The question is why? How can I fix that?

Answer 1

It's supposed to do that. If you start it as sh, it assumes you want something that's mostly compatible with other shells called sh, and runs in a compatibility mode.

See http://zsh.sourceforge.net/Doc/Release/Invocation.html#Compatibility:

Zsh tries to emulate sh or ksh when it is invoked as sh or ksh respectively; [...]

In sh and ksh compatibility modes the following parameters are not special and not initialized by the shell: ... prompt, PROMPT, ...

The usual zsh startup/shutdown scripts are not executed.

I'm not sure if it's possible to have not work in compatibility mode when called as sh, but that might break a number of scripts on your system that assume /bin/sh is just sh, not Zsh.

Probably best to run it as zsh instead.

Answer 2

Why not change your user's default shell using chsh instead.

$ chsh -s /usr/bin/zsh

References

• Installing ZSH