> gcc -g -O2 -Wall -o vchkpw vchkpw.o libvpopmail.a -L/root/mysql/lib/mysql
>-lmysqlclient -lz -lnsl -lcrypt -lm
> /usr/bin/ld: cannot find -lz
That means that zlib ist missing.
> What is the -lz all about (I am a long way from being any kind of programmer...)
"-l" specifies a library which gcc should link against. After "-l"
follows the name of that library, in your case "z". It means the file
/usr/lib/libz.so, which doesn't seem to be installed on your system.
On Debian, you should install the zlib1g[-dev] package.