I have done this process several times now without problems.
Run virtual box, install ubuntu 64bit, following the steps here:
https://openwrt.org/docs/guide-developer/quickstart-build-images
compile my own version what I need, install, configure, runs..
stable for several years and keep doing this to update once in a while.
Now I installed Ubuntu 18.04 LTS and also tried 18.10 version..
same steps as always..
but errors..
upon the ./scripts/feeds install -a
I get the messages:
WARNING: Makefile 'package/utils/busybox/Makefile' has a dependency on 'libpam', which does not exist.
WARNING: Makefile 'package/utils/busybox/Makefile' has a build dependency on 'libpam', which does not exist.
WARNING: Makefile 'package/network/utils/curl/Makefile' has a dependency on 'libgnutls', which does not exist.
WARNING: Makefile 'package/network/utils/curl/Makefile' has a dependency on 'libopenldap', which does not exist.
WARNING: Makefile 'package/network/utils/curl/Makefile' has a dependency on 'libidn2', which does not exist.
WARNING: Makefile 'package/network/utils/curl/Makefile' has a dependency on 'libssh2', which does not exist.
WARNING: Makefile 'package/boot/kexec-tools/Makefile' has a dependency on 'liblzma', which does not exist.
WARNING: Makefile 'package/network/services/lldpd/Makefile' has a dependency on 'libnetsnmp', which does not exist.
WARNING: Makefile 'package/network/utils/nftables/Makefile' has a dependency on 'jansson', which does not exist.
upon compiling it already errors just with default make menuconfig, not changing anything..
just errors and breaks out of the compilation.