doesn't find libruby-1.9.1 on ubuntu

System:

# uname -a
Linux ************* 2.6.18-128.2.1.el5.028stab064.8 #1 SMP Fri Nov 6 12:26:59 MSK 2009 i686 GNU/Linux

# webroar install
Checking for the dependencies ...
Checking for ruby........found   at /usr/local/bin/ruby.
Checking for libruby.so.1.9.1........not found.
Checking for openssl-ruby........found.
Checking for zlib-ruby........found.
Checking for ruby_headers........found   at /usr/local/include/ruby-1.9.1/ruby.h.
Checking for rubygems........found.
Checking for gcc........found   at /usr/bin/gcc.
Checking for make........found   at /usr/bin/make.
Checking for libsqlite3.so........found   at /usr/lib/libsqlite3.so.
Checking for sqlite3.h........found   at /usr/include/sqlite3.h.
Checking for starling........found   at /usr/local/bin/starling.
The following dependencies required for installation could not be found:
libruby.so.1.9.1
Please refer the user guide for the list of prerequisites.
Sorry, WebROaR could not be installed on this machine.

but

# aptitude search libruby1.9.1
i A libruby1.9.1                                                     - Libraries necessary to run Ruby 1.9.1

and

# ls -lash libruby-1.9.1.so*
   0 lrwxrwxrwx 1 root root   20 2009-12-08 22:17 libruby-1.9.1.so -> libruby-1.9.1.so.1.9
   0 lrwxrwxrwx 1 root root   22 2009-11-15 07:07 libruby-1.9.1.so.1.9 -> libruby-1.9.1.so.1.9.1
1.7M -rw-r--r-- 1 root root 1.6M 2009-10-04 19:39 libruby-1.9.1.so.1.9.1