I have worked with Interbase for a long time. Moved to Friebird a
couple years back and had problems getting 1.5 to work so stuck to 1.0.3.

I develop on Sun Solaris right now (hoping to see that one soon)!
However my target is Linux (Fedora) and I have been using Classic
for some historical performance reasons. Probably should move to Super
Server, but anyway - here is the problems I have encountered trying to
get 1.5.2 up with Classic implementation.

1) UDFS - used restrict UDF and put libraries under /opt/firebird/UDF
I had to rename the file (was SIS_udf to libSISudf.so to get
engine to find the file
problem 1: engine cannot find functions in library (was working
before and a unix "file" command of all udf files there says they are
all stripped shared objects
problem 2: why do the supplied firebird and interbase udf
libraries not need lib prefix (minor issue, but curious) - I must use
it even though my udfs say the name declaration was SIS_udf (changing)

2) most strange - cannot get a remote connection to work at all
Fedora uses xinetd - so I copied the supplied file to
/etc/xinetd.d/firebird
tried both HUP and USR2 (then reboot) on xinetd
all to no avail - netstat does not find a service on 3050
finally I manually start the daemon (fb_inet_server) from the
command line and it does not complain (nor do anything)