Hi Rainer, On Feb 17 20:37, Rainer Emrich via Cygwin wrote: > Am 17.02.2025 um 18:00 schrieb Corinna Vinschen via Cygwin: > > On Feb 17 12:51, Rainer Emrich via Cygwin wrote: > > > I'm facing a strange major issue with scp. The issue exists in all cygwin > > > version later than 3.5.3, > > > including cygwin-3.6.0-0.374.g4dd859d01c22. > > > > > > If I'm copying a large file with scp I get a "connection lost" after a > > > random couple of seconds: > > > > > > scp -v large_file foobar: > > > . > > > . > > > debug1: Sending subsystem: sftp > > > debug1: pledge: fork > > > large_file 10% 71MB > > > 4.3MB/s 02:21 ETA > > > debug1: client_input_channel_req: channel 0 rtype exit-status reply 0 > > > debug1: client_input_channel_req: channel 0 rtype e...@openssh.com reply 0 > > > debug1: channel 0: free: client-session, nchannels 1 > > > Transferred: sent 92266460, received 35436 bytes, in 15.3 seconds > > > Bytes per second: sent 6035219.0, received 2317.9 > > > debug1: Exit status 11 > > > lost connection > > > > In fact, I can reproduce this occassionally back to 3.5.0 and back to > > OpenSSH 9.7p1. We can't easily try this with older Cygwin versions. > > It's getting increasingly hard to build older Cygwin versions due to > > compiler dependencies and missing symbols. > at least for my file size, around 700MB, I can't reproduce this with cygwin > 3.5.3. I noticed this issue for the first time in the autumn last year. > > > What that means in the first place, is that this is neither a regression > > from 3.5.7, nor even from 3.5.1. Obviously I can't prove if this has > > been introduced into 3.5.0, but I'd like to point out that we didn't > > have any noticable change in the socket code for almost 4 years, back > > during 3.3 development. > > > > Fun fact: I can NOT reproduce the problem when using the -O option, > > i. e., when using the old scp protocol. The old protocol isn't > > slower either. > > > > Maybe that's a workaround for you? > > I try this, thanks.
I'm debugging this problem on and off for the last couple of days, and even discussing it with one of the upstream OpenSSH maintainers. But it's still a mystery to me. The "lost connection" message does not really point to the cause of the problem, it's just a followup effect: The server receives an EPIPE on the read socket, which in turn results in the clientside ssh to receive an "end-of-write" packet from the server, which in turn results in ssh closing the pipe to scp, which in turn prints the "lost connection" message. The only thing I can say so far is that it appears to be signal related. Fact is, that scp usually runs a SIGALRM triggered progressmeter. If you disable the progressmeter by running scp with the -q option, you can avoid the "lost connection" as well, you don't have to ron scp -O. > > > The strange thing, if I use strace to debug this, the cpoy succeeds: > > > strace -efno strace.log scp -v large_file foobar: > > > > This often points to a timing issue, but beats me where that could be. > > > > > I would try to debug this further, if I had an idea how to do that. > > > > Same here ATM, sorry. > > That's really strange. Yeah, I know. But it's really tricky. All my debugging so far only turned up followup effects, not the actual cause. Sigh. Corinna -- Problem reports: https://cygwin.com/problems.html FAQ: https://cygwin.com/faq/ Documentation: https://cygwin.com/docs.html Unsubscribe info: https://cygwin.com/ml/#unsubscribe-simple
