rsync takes long time to start

Question

I'm running on Ubuntu 18.04 and the rsync command takes a long time to start. Given a file to transfer of 0 byte, it still takes more than 5 seconds to transfer.

Version of rsync: 3.1.2

time rsync rsync://192.168.0.105/small_file test
real    0m5.145s
user    0m0.000s
sys 0m0.003s

I've checked:

testing different options of rsync
using another Ubuntu 18.04 with same version of rsync: the transfer takes less than 100ms
using ssh, ping or scp to test if the network is slow: nothing wrong
the DNS resolution delay is ok
ram & cpu are ok

I'm running out of ideas to check and the verbose mode (-v) is not helpfull

Any idea of what the problem could be ? Or how I could debug it ?

Thanks !

Have you tried running with -vvv to see if more debug information shows you where the slowdown happens? Can you try using ssh as the medium for the sync rather than the rsync protocol itself? — Shadur-don't-feed-the-AI, Sep 27 '23 at 09:26
The '5 seconds' delay sounds to me like there's a DNS lookup timing out somewhere. — Shadur-don't-feed-the-AI, Sep 27 '23 at 09:26
-vvv has the exact same output on the server where it's slow and on the server where it's fast :( — Julien Greard, Sep 27 '23 at 09:57
Regarding the DNS, yes, I thought the same but I'm using the IP address directly and when I ping it, it works directly with no delay — Julien Greard, Sep 27 '23 at 09:57
I know you're using the IP address, but it may be that the receiving rsync host is attempting a DNS lookup either for logging purposes or to verify a whitelist. — Shadur-don't-feed-the-AI, Sep 27 '23 at 09:59
Check logs on the other end. If rsync or rhost is running as a daemon it should be logging something. — Shadur-don't-feed-the-AI, Sep 27 '23 at 10:39
Alternately, you can just use ssh as the transfer mode and not have to worry about it at all -- more secure anyway. — Shadur-don't-feed-the-AI, Sep 27 '23 at 10:40
@JulienGreard the -vvv may provide the same output, but you can probably see between which lines the lag appears, and that might give you some hint. Start by prepending timestamp to your rsync commands, see between each lines there's the largest gap, it might direct you to some lead. — aviro, Sep 27 '23 at 11:45
That was it thx @Shadur !! https://superuser.com/questions/198516/rsync-hangs-with-message-name-lookup-failed-for-xxx-xxx-xxx-xxx-no-address-ass. I had a "name lookup failed for" line in syslog, I changed the options in the config of rsync daemon and i worked — Julien Greard, Sep 27 '23 at 12:58

score 0 · Accepted Answer · edited Sep 27 '23 at 13:27

0

The problem was solved by setting the reverse lookup settings to no in the rsync daemon.

edited Sep 27 '23 at 13:27

Jeff Schaller

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answered Sep 27 '23 at 13:00

Julien Greard

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This indicates that the problem has to do with DNS configuration. What you did was to work around the problem, without actually solving it, IMHO. – Kusalananda Sep 27 '23 at 16:07
True, but we're fine with the workaround – Julien Greard Oct 03 '23 at 16:11

rsync takes long time to start

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