rsync 3.5.1 wrongly listens on IP adress rather than socket

@steadytao

We just updated our fleet in Arch Linux to the latest rsync release and following that, saw all of our mirrors fail to synchronize due to the following error:

[2026-10-07T12:59:06+0000] [ALPM] upgraded rsync (3.5.0-1 -> 3.5.1-1)

Oct 07 17:40:34 repos.archlinux.org rsyncd[283295]: rsyncd version 3.5.1-g04355d27 starting, listening on port 873
Oct 07 17:40:34 repos.archlinux.org rsyncd[283295]: bind() failed: Address already in use (address-family 2)
Oct 07 17:40:34 repos.archlinux.org rsyncd[283295]: bind() failed: Address already in use (address-family 10)
Oct 07 17:40:34 repos.archlinux.org rsyncd[283295]: unable to bind any inbound sockets on port 873
Oct 07 17:40:34 repos.archlinux.org rsyncd[283295]: rsync error: error in socket IO (code 10) at socket.c(707) [Receiver=3.5.1-g04355d27]

https://gitlab.archlinux.org/archlinux/infrastructure/-/work_items/876

Upon investigating the issue it turns out that downgrading rsync to 3.5.0 fixes the issue (archlinux/infrastructure!1244), looking through the 3.5.0..3.5.1 changelog it seems like #1075 could be a potential culprit for the issue. (cc @steadytao & @schuelermine)

A few words about our setup (all infrastructure as code can be found in https://gitlab.archlinux.org/archlinux/infrastructure/ in the dbscripts role):

We set an override via /etc/systemd/system/rsyncd.socket.d/override.conf to make the socket listen on a local socket:

[Socket]
ListenStream=
ListenStream=/run/rsyncd.sock

And then proxy to that both SSL and non-SSL traffic so that our mirrors can use it via rsync-ssl:

server {
    listen 873;
    listen [::]:873;

    access_log /var/log/nginx/rsync.archlinux.org/stream.log stream;
    access_log /var/log/nginx/rsync.archlinux.org/stream.log.json json_stream;
    error_log  /var/log/nginx/rsync.archlinux.org/stream.error.log;

    proxy_pass unix:/run/rsyncd.sock;
    proxy_protocol on;
}

server {
    listen      874 ssl;
    listen      [::]:874 ssl;
    server_name rsync.archlinux.org;

    access_log  /var/log/nginx/rsync.archlinux.org/stream.log stream;
    access_log  /var/log/nginx/rsync.archlinux.org/stream.log.json json_stream;
    error_log   /var/log/nginx/rsync.archlinux.org/stream.error.log;

    ssl_certificate     /etc/letsencrypt/live/repos.archlinux.org/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/repos.archlinux.org/privkey.pem;

    proxy_pass unix:/run/rsyncd.sock;
    proxy_protocol on;
}

cc @Antiz96 @jelly

Here is an explanation of the underlying bug (🤖 -assisted):

daemon_main() in clientserver.c decides whether it was started by inetd (or by a systemd socket unit with Accept=yes) by calling is_inetd_socket(STDIN_FILENO). This replaced the old is_a_socket() check, which returned true for any socket on stdin.

The new function only returns true if stdin is:

a SOCK_STREAM socket, and
connected, with a peer address family of AF_INET or AF_INET6.

With ListenStream=/run/rsyncd.sock, stdin is a connected AF_UNIX stream socket, so is_inetd_socket() returns 0. The daemon then doesn't take the inetd path and goes on to start_accept_loop() -> open_socket_in(), which tries to bind port 873. That fails with:

bind() failed: Address already in use (address-family 2)
unable to bind any inbound sockets on port 873

In 3.5.0 is_a_socket() accepted the AF_UNIX socket, so this setup worked.

Skip rsync upgrade to 3.5.1 on mirrors and repos servers

@christian-heusel

@christian-heusel Thank you for reporting. We have had some other reports submitted to us we are working through but a release should hopefully be rolled out somewhat soon. If desired, you may replay #1121 onto a patch for 3.5.1 on Arch.

@steadytao

Thanks a lot, @steadytao !

As a quick fix we reverted 7ee931c yesterday... @christian-heusel do we want to cherry-pick 6eb05b3 instead and push just another package?

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rsync 3.5.1 wrongly listens on IP adress rather than socket #1119

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rsync 3.5.1 wrongly listens on IP adress rather than socket #1119

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christian-heusel commented on Oct 7, 2026

steadytao commented on Oct 8, 2026

eworm-de commented on Oct 8, 2026

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