• https://wiki.debian.org/CrossGrading

1. Add the new architecture

   dpkg --print-architecture
   # i386
    
   dpkg --add-architecture amd64
    
   dpkg --print-foreign-architectures
   # amd64
    
   apt-get update

2. Install a kernel that supports both architectures in userland

   apt-get install linux-image-amd64:amd64
    
   reboot

3. Crossgrade dpkg tar and apt

   apt-get clean
    
   apt-get upgrade
    
   apt-get --download-only install dpkg:amd64 tar:amd64 apt:amd64
    
   dpkg --install /var/cache/apt/archives/*_amd64.deb
    
   dpkg --print-architecture
   # amd64
    
   dpkg --print-foreign-architectures
   #i386

4. Swap arch of libs

   dpkg --get-selections \
       | grep ':i386' \
           | sed -e 's/:i386/:amd64/' \
               | dpkg --set-selections
    
   apt-get -f install

1. Architektúra beállítása (/etc/apt/apt.conf.d/00arch):

   00arch

   APT::Architectures "amd64,i386";

2. apt takarítása

   apt-get clean
    
   rm -rf '/var/lib/apt/lists'
    
   apt-get update

3. dpkg available újragenerálása

   dpkg --clear-avail
    
   du '/var/lib/dpkg/available'
   # 0       /var/lib/dpkg/available
    
   find '/var/lib/apt/lists' -name '*_Packages' -exec dpkg --merge-avail {} \;
    
   du '/var/lib/dpkg/available'
   # 67872   /var/lib/dpkg/available