Configure ssh to behave like rsh. How?

[Rob]

Hi,

I have a cluster of PCs, on which the 'slaves' used to only allow rsh
connections, to execute commands, but no logins.

I have removed the r-commands, and want to use the ssh command family
instead. Although 'ssh slaveN command' works fine, this also allows login
to the slave PC, simply by typing 'ssh slaveN'.

How can I configure sshd, so that it will allow remote command execution,
but will refuse logins?

Thanks,
Rob.