/usr/bin/perl: symbol lookup error: lib/x86_64-linux-gnu-thread-multi/
+auto/DBD/SQLite/SQLite.so: undefined symbol: Perl_Istack_sp_ptr
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Looks like your Bugzilla installation has its own DBD::SQLite module¹, and this module had been built with the previous perl (meaning it's binary incompatible with the newer perl).

I don't know why your Bugzilla came with its own version of DBD::SQLite instead of using the existing Debian/Ubuntu package, but you might want to try installing the latter package (sudo apt-get install libdbd-sqlite3-perl) and see how things go.

You probably then also want to ditch/rename the bugzilla-private version to ensure the regular Ubuntu package is in fact being pulled in (for testing purposes, at a minimum, rename both the SQLite.so and the SQLite.pm files below ./lib/).

it surprizes me that when i run ./checksetup.pl the identified mysql version is 4..020 when i have installed v 5.5.22

The reported 4.020 is the version of the DBD-mysql Perl binding, not of mysql itself.  This has nothing to do with the actual, above mentioned, problem.

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¹ the installation path of the regular Ubuntu package would be

/usr/lib/perl5/auto/DBD/SQLite/SQLite.so
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not

./lib/x86_64-linux-gnu-thread-multi/auto/DBD/SQLite/SQLite.so
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