Mono 6.12.0 Release Notes says that’s a November 2020 version. Maybe try a newer download?
Although I couldn’t find a relevant mono project issue, one never knows. Technically it died in libc.
getpwuid_r might be trying to fetch names (reverse-lookup from number) for the owner and group.
Looking at a sample block of metadata from a Linux dblock file, its format does store such names.
Aug 9 20:59:31 fedora duplicati-server[259594]: #011 at Mono.Unix.Native.Syscall:sys_getpwuid_r <0x000a8>
Aug 9 20:59:31 fedora duplicati-server[259594]: #011 at Mono.Unix.Native.Syscall:getpwuid_r <0x00077>
Aug 9 20:59:31 fedora duplicati-server[259594]: #011 at Mono.Unix.UnixUserInfo:.ctor <0x00087>
Aug 9 20:59:31 fedora duplicati-server[259594]: #011 at Mono.Unix.UnixFileSystemInfo:get_OwnerUser <0x0006b>
Aug 9 20:59:31 fedora duplicati-server[259594]: #011 at FileInfo:.ctor <0x000b3>
Aug 9 20:59:31 fedora duplicati-server[259594]: #011 at UnixSupport.File:GetUserGroupAndPermissions <0x00057>
Aug 9 20:59:31 fedora duplicati-server[259594]: #011 at Duplicati.Library.Common.IO.SystemIOLinux:GetMetadata <0x001eb>
Aug 9 20:59:31 fedora duplicati-server[259594]: #011 at Duplicati.Library.Snapshots.NoSnapshotLinux:GetMetadata <0x0005a>
Aug 9 20:59:31 fedora duplicati-server[259594]: #011 at Duplicati.Library.Main.Operation.Backup.MetadataGenerator:GenerateMetadata <0x00121>
I don’t know why a lookup would fail though. Perhaps ltrace could confirm the call where it aborts.
That’s too bad, otherwise I’d wonder if it found a file that killed it, and ask for narrowing area down.
There’s still a chance it’s file-specific. You could run a verbose log-file to see how random death is.
Channel Pipeline tries to explain internals. Source code has GenerateMetadata uses in these files
https://github.com/duplicati/duplicati/blob/master/Duplicati/Library/Main/Operation/Backup/FilePreFilterProcess.cs
https://github.com/duplicati/duplicati/blob/master/Duplicati/Library/Main/Operation/Backup/MetadataPreProcess.cs
So there are some debug ideas to try to find why mono is dying. Of course it’s not supposed to die…
Aug 9 20:59:33 fedora systemd[1]: duplicati.service: Main process exited, code=exited, status=134/n/a
From Google search, 134 may be what mono does when it dies this way. That’s not a Duplicati code.