Showed Internal server
Opened the following file to view the error log
sudo gedit /var/log/koha/library/plack-error.log
It is showing something like
Error while loading /etc/koha/plack.psgi: Can't load application from file "/usr/share/koha/api/v1/app.pl": Can't open /var/log/koha/library/z3950-error.log (Permission denied) at /usr/share/perl5/Log/Log4perl/Appender/File.pm line 151.
Applied following commands to fix it
sudo chown library-koha:library-koha /var/log/koha/library/z3950-error.log
sudo chown -R library-koha:library-koha /var/log/koha/library/
sudo chmod -R 750 /var/log/koha/library/
sudo koha-plack --restart library
Now it is OK
