I think the job log isn’t saved until backup finishes, which means (unfortunately) that it’s not there to help when the backup has a problem before finishing. The email report seems to scrape some data out that’s nowhere else, but it’s still just bits and pieces. Ideally a problem that’s reproducible can get a –log-file at some tolerably wordy level, but it’s not something most people (or Duplicati by default) normally will run.
Backup failing: “Path cannot be null” and “TLS warning: SSL3 alert write: fatal: bad record mac”
was located by Google as something similar to your stack trace except it adds another one that possibly makes more sense for “Parameter name: path” and “Path cannot be null” error. A generous quote is like
2020-02-24 13:52:49 -04 - [Information-Duplicati.Library.Main.BackendManager-RenameRemoteTargetFile]: Renaming "duplicati-ia869d67054c24dd9a073856c903b2f94.dindex.zip.aes" to "duplicati-idc8b6aaaa58349af9bba024a83907605.dindex.zip.aes"
2020-02-24 13:52:59 -04 - [Retry-Duplicati.Library.Main.BackendManager-RetryPut]: Operation Put with file duplicati-idc8b6aaaa58349af9bba024a83907605.dindex.zip.aes attempt 5 of 5 failed with message: Path cannot be null.
Parameter name: path
System.ArgumentNullException: Path cannot be null.
Parameter name: path
at System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy, Boolean useLongPath, Boolean checkHost)
at System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share)
at Duplicati.Library.Encryption.EncryptionBase.Encrypt(String inputfile, String outputfile)
at Duplicati.Library.Main.BackendManager.FileEntryItem.Encrypt(IEncryption encryption, IBackendWriter stat)
at Duplicati.Library.Main.BackendManager.DoPut(FileEntryItem item)
at Duplicati.Library.Main.BackendManager.ThreadRun()
2020-02-24 13:52:59 -04 - [Information-Duplicati.Library.Main.BasicResults-BackendEvent]: Backend event: Put - Failed: duplicati-idc8b6aaaa58349af9bba024a83907605.dindex.zip.aes ()
2020-02-24 13:52:59 -04 - [Error-Duplicati.Library.Main.Operation.BackupHandler-FatalError]: Fatal error
System.ArgumentNullException: Path cannot be null.
Parameter name: path
at Duplicati.Library.Main.BackendManager.WaitForEmpty(LocalDatabase db, IDbTransaction transation)
at Duplicati.Library.Main.Operation.CompactHandler.DoDelete(LocalDeleteDatabase db, BackendManager backend, IEnumerable`1 deleteableVolumes, IDbTransaction& transaction)
at Duplicati.Library.Main.Operation.CompactHandler.DoCompact(LocalDeleteDatabase db, Boolean hasVerifiedBackend, IDbTransaction& transaction, BackendManager sharedBackend)
at Duplicati.Library.Main.Operation.DeleteHandler.DoRun(LocalDeleteDatabase db, IDbTransaction& transaction, Boolean hasVerifiedBacked, Boolean forceCompact, BackendManager sharedManager)
at Duplicati.Library.Main.Operation.BackupHandler.CompactIfRequired(BackendManager backend, Int64 lastVolumeSize)
at Duplicati.Library.Main.Operation.BackupHandler.<RunAsync>d__20.MoveNext()
and I’m not familiar enough with the code to know exactly how these two stack trace might be related.
At a high level, this looks like the compact that runs after the backup and after deletions done by your retention policy had an issue. I just filed 403 error during compact forgot a dindex file deletion, getting Missing file error next run. #4129 (whose title might change because it’s now broadened in its scope).
You could consider filing yours as an issue so that it will be in the queue for the developers to look at. Whether or not it’s the cause of “The process cannot access the file” isn’t clear, but fixing that will be much more likely if it’s reproducible, and sometimes this means finding a lead-in Thanks for the data.