Re: Systemd socket inheritance fails with “not a socket file descriptor”

[Eric Wong <e@80x24.org>]

Amir Yalon <amiryal@yxejamir.net> wrote:
> Starting the systemd service with a configuration based on
> http://bogomips.org/unicorn-public/20150708130821.GA1361@luke.ws.skroutz.gr/
> (also found under examples/ in the source code), it fails, and the
> following is seen in the systemd journal:
>  
> > app/vendor/bundle/ruby/2.0.0/gems/unicorn-5.0.1/lib/unicorn/http_server.rb:780:in `for_fd': not a socket file descriptor (ArgumentError)

<snip>
 
> The error, in `for_fd': not a socket file descriptor (ArgumentError),
> occurs when attempting `io = Socket.for_fd(fd.to_i)`.

Curious, that means it's failing at the S_ISSOCK at line 53:

http://bogomips.org/mirrors/ruby.git/tree/ext/socket/init.c?h=v2_0_0_645#n53

fstat() says it's a valid FD, but not a socket.  Maybe IO.for_fd
can enlighten us as to what you're getting if it's not a socket.

Can you try the following change to http_server.rb to dump out
the stat info of the FD that's failing?

It'll still fail at Socket.for_fd, but IO.for_fd should not fail
since fstat() already succeeded.

--- a/lib/unicorn/http_server.rb
+++ b/lib/unicorn/http_server.rb
@@ -777,6 +777,9 @@ def inherit_listeners!
     # to ease debugging, we will not unset LISTEN_PID and LISTEN_FDS
 
     inherited.map! do |fd|
+      io = IO.for_fd(fd.to_i)
+      io.autoclose = false
+      $stderr.write("fd=#{fd.inspect} #{io.stat.inspect}\n")
       io = Socket.for_fd(fd.to_i)
       io.autoclose = false
       io = server_cast(io)

Also, can you verify the UNICORN_FD env is NOT set by systemd?
(It should not be)

Thanks.

> Using Ruby version 2.0.0p645.  Should I try using 2.2 or later?

If it's easy, sure; but I just tried with 2.0.0-p645 without
problems; so I would try making the change above and verifying
UNICORN_FD is not set when systemd is being used, first.

Ruby itself could not emulate systemd behavior for testing until
2.3.0, but the actual functionality of unicorn w/ systemd should
not be diminished with a real systemd with older Rubies.


Also, for reference, which version of systemd is this?

I checked the latest systemd.git but didn't notice any changes
which would break the expectations of our sd_listen_fds(3)
function emulation:

	git clone https://github.com/systemd/systemd.git
	cd systemd && git log -p src/libsystemd/sd-daemon/

But maybe I missed something...
Fwiw, I tested on Debian jessie w/ systemd 215-17+deb8u3