I updated to Windows 10 Pro 1903 build 18362.207 and enabled WSL. I then installed Debian GNU/Linux 1.1.6.0 from the Microsoft Store. My urbackup client is 2.3.4
I now get 62 errors the first of which is below, the other 61 are similar:
Error getting complete file “aQy7jUQJkBFS8tUEHNkB|Users/phil/AppData/Local/Packages/TheDebianProject.DebianGNULinux_76v4gfsz19hv4/LocalState/rootfs/usr/lib/x86_64-linux-gnu/perl/5.24.1/sys/Hostname.pm” from beryl. Errorcode: CANNOT_OPEN_FILE (3)
Looking at the directory \wsl$\Debian\usr\lib\x86_64-linux-gnu\perl\5.24.1\ I see both a Sys and a sys directory.
The Hostname.pm file is in Sys rather than sys so urbackup would find it as aQy7jUQJkBFS8tUEHNkB|Users/phil/AppData/Local/Packages/TheDebianProject.DebianGNULinux_76v4gfsz19hv4/LocalState/rootfs/usr/lib/x86_64-linux-gnu/perl/5.24.1/Sys/Hostname.pm I assume.
In researching this I found Do not change Linux files using Windows apps and tools which recommends WSL File System Support for more details.
The case handling on the two filesystem types differ and I think it is confusing the urbackup client. In general my NTFS system is case insensitive but WSL changes it to case sensitive for any file actions it uses.
The warning about accessing the files causes me to wonder if it could be restored from backup anyway, it would depend on exactly what urbackup copies for each file.
While excluding the two directories with differing case would stop the errors I don’t think it is the correct solution.
If urbackup was case sensitive and copied all file streams I think the backup/restore might work. If it does not copy all streams it will not restore successfully and I cannot use urbackup for the WSL areas of my system.