Release version 3.4.0

-a implies -D, so a generation was written with --devices --specials and rsync recreated every unix socket and fifo it found in a volume. On the swarm manager that generation lives on an nfs-ganesha export, and ganesha accepts the socket on write but cannot serve it back: the remote pull's sender then fails with readdir/readlink_stat 'Invalid argument (22)' and exits 23, deterministically, for all twelve retries - 58 minutes per run.

Postfix's queue directory is the case that surfaced it, where public/ and private/ hold roughly fifty AF_UNIX sockets and nothing else. The class is wider: a discourse /shared with its in-container postgres socket, a checkmk OMD site with tmp/run/nagios.cmd, a container whose /tmp is a persisted volume. --no-D is type-based and closes all of them without anyone having to know which image binds a socket where.

Nothing restorable is lost. A socket inode is meaningless after a restore; postfix's master, checkmk's omd start and discourse's supervisor recreate theirs. The whole postfix queue survives - incoming, active, deferred, hold, maildrop - so accepted-but-undelivered mail stays in the backup, which excluding the volume outright would have dropped. Device nodes go too, and the only volume that could hold them is a nested docker data root, already carrying backup: false.

This is the writer side, whose source is a local docker volume. On the reader the same flag provably does nothing: rsync still stats the entry before -D decides, and getdents64 on the containing directory is outside its reach entirely.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -1,5 +1,20 @@
 # Changelog
 
+## [3.4.0] - 2026-08-02
+
+- Backup: *-a* implies *-D*, so a generation was written with
+  *--devices --specials* and rsync recreated every unix socket and fifo found in
+  a volume. Where the backup root is an nfs-ganesha export, ganesha accepts the
+  socket on write but cannot serve it back, and the remote pull's sender then
+  fails with *readdir* / *readlink_stat* "Invalid argument (22)" and exits 23 —
+  deterministically, for every retry. *--no-D* keeps them out of the generation.
+- Backup: nothing restorable is lost. Sockets and fifos are recreated by the
+  daemons that own them, and the postfix queue itself — *incoming*, *active*,
+  *deferred*, *hold*, *maildrop* — is unaffected, so accepted-but-undelivered
+  mail stays in the backup. Device nodes go too; the only volume that could hold
+  them is a nested docker data root, which does not belong in a backup anyway.
+- Tests: the flag is asserted on the rsync invocation.
+
 ## [3.3.0] - 2026-08-02
 
 - Backup: *--volumes-no-backup-required* excludes a volume by name.

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "backup-docker-to-local"
-version = "3.3.0"
+version = "3.4.0"
 description = "Backup Docker volumes to local with rsync and optional DB dumps."
 readme = "README.md"
 requires-python = ">=3.9"

src/baudolo/backup/volume.py

@@ -49,7 +49,10 @@ def backup_volume(
     link_dest = f"--link-dest='{last}'" if last else ""
     verify = "--checksum " if authoritative else ""
 
-    cmd = f"rsync -abP --delete --delete-excluded {verify}{link_dest} {source} {dest}"
+    cmd = (
+        f"rsync -abP --no-D --delete --delete-excluded "
+        f"{verify}{link_dest} {source} {dest}"
+    )
 
     try:
         execute_shell_command(cmd)

tests/unit/backup/test_volume.py

@@ -43,6 +43,9 @@ class TestBackupVolume(unittest.TestCase):
     def test_it_always_deletes_what_the_source_no_longer_has(self) -> None:
         self.assertIn("--delete", self.copy())
 
+    def test_it_carries_no_kernel_objects_into_a_generation(self) -> None:
+        self.assertIn("--no-D", self.copy())
+
     def test_it_creates_the_destination(self) -> None:
         with tempfile.TemporaryDirectory() as tmp:
             dest = Path(tmp) / "gen" / "demo"