If you are getting an error "The Runtime User ID does not exist. Specify a valid UNIX user." while installing Sun Java System Web Server on Mandriva, all you have to do is create a softlink as shown below. Its simple !
#ln -s /bin/id /usr/bin/id
You can also check if /usr/bin/cat exists or not. If it doesn't, then you have to create a softlink as given below
#ln -s /bin/cat /usr/bin/cat
\*Note that Sun Java System Web Server is not officially certified or supported on Mandriva