change default shell from zsh to bash

Make sure /usr/bin/chsh has execute permissions by running sudo chmod a+x /usr/bin/chsh.

You should be able to run chsh using your own account. Otherwise you'd be setting root's shell. Try the following:

chsh -s $( which bash )

Maybe your default shell is already bash.

To know your default shell on Red Hat:

finger youruser

output:

Login: XXXXXXXX                         Name: XXXXXX XXXXXX
Directory: /Home/XXXXXX                 Shell: /bin/zsh
Office: XXXXXX
Office Phone: XXXXXXXXXX                Home Phone: XXXXXXXXXX
...

If the Shell information is not /bin/bash then use ypchfn:

$ ypchsh
Changing NIS account information for XXXX on XXXXXXXXX.
Please enter password:

Changing login shell for XXXX on XXXXXXXXX.
To accept the default, simply press return. To use the
system's default shell, type the word "none".
Login shell [/bin/zsh]: /bin/bash

The login shell has been changed on XXXXXXXXX.

Check again your default shell:

finger youruser

output:

Login: XXXXXXXX                         Name: XXXXXX XXXXXX
Directory: /Home/XXXXXX                 Shell: /bin/bash
Office: XXXXXX
Office Phone: XXXXXXXXXX                Home Phone: XXXXXXXXXX
...

Let me know if it is OK for you... Cheers