rsync failed to set permissions for a local copy ("Function not implemented")

Question

There are lots of similar questions out there, but none seems to address my problem: every time, the culprit is a legitimate permission issue, or an incompatible filesystem, none of which makes any sense here.

I'm transferring a file locally, on an ext4 filesystem, using rsync. A minimal example is:

cd /tmp
touch blah
mkdir test
rsync -rltDvp blah test

which returns the error:

rsync: [receiver] failed to set permissions on "/tmp/test/.blah.Gyvvbw": Function not implemented (38)

and the files have different permissions:

-rw-r--r-- 1 ted ted 0 Sep 29 15:49 blah
-rw------- 1 ted ted 0 Sep 29 15:49 test/blah

I'm running rsync as user ted and the filesystem is ext4, so it should support permissions just fine. Here is the corresponding line from df -Th:

Filesystem                  Type        Size  Used Avail Use% Mounted on
/dev/mapper/c--3px--vg-root ext4        936G  395G  494G  45% /

I'm running rsync 3.2.3 protocol version 31 on Debian Sid, kernel 5.10.0-6-amd64.

Answer 1

The OP wrote,

apt-get update && apt-get upgrade, which apparently upgraded rsync (to version 3.2.3-8), fixed the problem.

The error was presumably caused by to a change to lchmod and fchmodat in the GNU C library.