# Issue Description
Between two systems (different OSs) both with rsync 3.1.3, copies fail with an unhelpful error when they use different ACL formats:
rsync: [sender] write error: Broken pipe (32)
rsync: connection unexpectedly closed (56591 bytes received so far) [generator]
rsync error: error in rsync protocol data stream (code 12) at io.c(820) [sender=3.1.3]
This is a nondescript error that sends the user down a rabbit hole debugging the wrong issue (are my rsync versions mismatched? why is there a protocol-level error? is my ssh connection failing? is my disk full?).
It doesn't help that by default logs or increasing sender-side verbose produces no further hints; it's only by increasing receiver-side verbosity with -M-vvv that I got to the bottom of it -- incompatible ACL systems:
recv_acl_access: "value out of range": 129a000
Once it became clear that it was an ACL issue, per the man page '-M--fake-super' fixes the issue.
# Repro steps
rsync -aAX macos-timemachine-backups-folder user@linuxhost:/path/to/dst
# Actual Results
rsync produces a bogus error about protocol failure, when in reality the protocol communication itself is just fine (receiver just has an unsupported ACL error)
# Expected Results
rsync produces a more appropriate error message, along the lines of "ACL unsupported by receiver"