When upgrading Vertica, it will check if bash is the default shell for the dbadmin user, and complain loudly if this is not the case:
Error: Default shell on the following nodes are not bash. Default shell must be set to bash. 10.0.0.1 for dbadmin: 10.0.0.2 for dbadmin: Exiting... Installation FAILED with errors.
Of course, if the shell is indeed not bash, you can fix it by running
chsh -s /bin/bash
on the relevant nodes as the dbadmin user.
In some cases, bash is indeed the shell, but due to ssh or sudo configuration, the installer does not see it. In that case, using visudo to edit the /etc/sudoers file just add the following lines:
Defaults:dbadmin !requiretty dbadmin ALL=(ALL) NOPASSWD:ALL
Those lines are needed only at install, and can be reverted afterwards.