With ubuntu 12.04 apache 2.2  lxr 1.3 

both

After step by step from the doc . and make a litte change in  in apache-lxrserver.conf 
------------------------------
Alias /lxr /usr/local/share/lxr/  # i add it , default  is none

<Directory "/usr/local/share/lxr">
        Options FollowSymLinks
        AllowOverride AuthConfig FileInfo Limit Options
                # Apache 2.2 access control
        Order allow,deny
                # up to Apache 2.2
        Allow from all
                # from Apache 2.4
#       Require all granted
</Directory>
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vist  localhost/source  ,  the webrowser show NULL 
/var/log/apache2/error.log show

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[Sat Aug  3 01:51:38 2013] fatal: Carp, line 79: mkdir swish: Permission denied at /usr/local/share/lxr/lib/LXR/Config.pm line 1102
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and with apt-get install libapache2-mod-perl2-dev 
and virtroot = lxr

Not Familiar with perl ,Does some one meet this ?