On Thu, Feb 18, 2016 at 12:02:48PM -0800, Simon Ruderich wrote: > # New Ticket Created by Simon Ruderich > # Please include the string: [perl #127566] > # in the subject line of all future correspondence about this issue. > # <URL: https://rt.perl.org/Ticket/Display.html?id=127566 > > > > Hello, > > I'm having a weird problem with run. In the following sample, > Perl6 waits after "slurping err" when the ssh mux process gets > spawned in the background on the initial connection. It waits > until the ssh mux process terminates on its own and then prints > the output (stdout/stderr) correctly. If the ssh mux process is > already running, everthing works fine. > > my @cmd = « > ssh > -o Protocol=2 > -o ControlMaster=auto > -o ControlPath=master-%l-%h-%r > -o ControlPersist=30 > »; > @cmd.append('root@steep', 'ls');
I don't think this is a Perl problem; I believe it may be a real OpenSSH bug (or, at least, unexpected behavior). The problem is that when your SSH client decides to start the mux process, the latter *does not close* its standard error stream; it keeps file descriptor 2 open to whatever the original SSH client had it open to - usually this is the user's terminal, but in your case, it's the pipe back to your program. Even though the original SSH client process exited, the pipe is still open (to another process, yet still open anyway), and Perl is absolutely correct to wait for everything that has the pipe open to close it. This does not even come from Perl, it's your OS's kernel doing it - but, since there is a process still using the pipe, it's correct to do it that way :( As far as I can see, this behavior - leaving fd 2 open to the original client's standard error stream - is not explicitly documented in either the ssh(1) manual page or the ssh_config(5) one. I've even tried passing the -E option to send the debug logs to someplace else, but it does indeed only affect the debug logs, not the actual standard error stream :( I wonder if it might be worthwhile to raise this with the OpenSSH developers; I could do that if you'd like me to. G'luck, Peter -- Peter Pentchev r...@ringlet.net r...@freebsd.org p...@storpool.com PGP key: http://people.FreeBSD.org/~roam/roam.key.asc Key fingerprint 2EE7 A7A5 17FC 124C F115 C354 651E EFB0 2527 DF13
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