plymouth always has a theme and is always used in the boot of Ubuntu, its just not obvious because servers use the
details theme which is in the
plymouth package itself.
Before running down the theme rabbit hole though, make sure you have added
quiet back into your
grub prompt. By default, servers do not have
quiet because administrators want to see the text that commands output as they start up (this was a change made in 11.04). You'll need the tool
debconf-utils to check it, then do:
debconf-get-selections | grep grub | grep quiet
If you see
noquiet in there, then that may be what is stopping your logo from appearing. Also if you see
nomodeset that will stop graphical boot. You can fix this with
sudo dpkg-reconfigure grub-pc
BE CAREFUL as those settings are vital to your system being bootable, so possibly consider doing a backup before changing them.
Now, if you do have
quiet mode on, and you want to have another theme chosen, you need only install it, and it should be set as the default. If you'd like to manually check what the default is, you can use the tool
$ update-alternatives --list default.plymouth
$ update-alternatives --display default.plymouth
default.plymouth - auto mode
link currently points to /lib/plymouth/themes/ubuntu-logo/ubuntu-logo.plymouth
/lib/plymouth/themes/ubuntu-logo/ubuntu-logo.plymouth - priority 100
slave default.plymouth.grub: /lib/plymouth/themes/ubuntu-logo/ubuntu-logo.grub
Current 'best' version is '/lib/plymouth/themes/ubuntu-logo/ubuntu-logo.plymouth'.
If you'd like to make the graphical logo appear on your server boot, it should be as easy as doing
sudo apt-get install plymouth-theme-ubuntu-logo
If that doesn't cause the default alternative to change to the output above, then you can always force the issue with:
sudo update-alternatives --config default.plymouth
Though that may just tell you there is only one choice. If you have
plymouth-theme-ubuntu-logo installed, and you've removed
nomodeset, and you have
quiet as a boot option, and you still get no plymouth theme then your graphics hardware may just be incapable of providing a graphical boot for your server.
plymouth-theme-ubuntu-text should at least give you the version and loading dots.