Comment 5 for bug 1903838

Method from Alan Orth (aorth) worked for me. To clarify, you need to get a copy of libcrypt.so.1.1.0 BEFORE attempting upgrade, as by the time it borks, you might have trouble getting the file onto the system, as many utils won't run.

For me, I got the file from here and extracted it:

http://mirrors.edge.kernel.org/ubuntu/pool/main/libx/libxcrypt/libcrypt1_4.4.10-10ubuntu4_amd64.deb

When the upgrade failed, cancelled out (x), and then copy, symlink and resume upgrade as detailed above.