When Borg Backup runs each file will show a status character, these are detailed below:

A uppercase character represents the status of a regular file relative to the “files” cache (not relative to the repo – this is an issue if the files cache is not used). Metadata is stored in any case and for A and M also new data chunks are stored. For U all data chunks refer to already existing chunks.

• A = regular file, added (see also I am seeing A (added) status for an unchanged file!? in the FAQ)
• M = regular file, modified
• U = regular file, unchanged
• C = regular file, it changed while we backed it up
• E = regular file, an error happened while accessing/reading this file

A lowercase character means a file type other than a regular file, borg usually just stores their metadata:

• d = directory
• b = block device
• c = char device
• h = regular file, hardlink (to already seen inodes)
• s = symlink
• f = fifo

Other flags used include:

• i = backup data was read from standard input (stdin)
• - = dry run, item was not backed up
• x = excluded, item was not backed up
• ? = missing status code (if you see this, please file a bug report!)

– borg create — Borg - Deduplicating Archiver 1.2.3 documentation