[systemd-devel] Is a socket with Accept=yes and ListenFIFO impossible?

[Steve Traylen]

On 05/09/2024 15:52, Mantas Mikulėnas wrote:
>
> FIFOs aren't sockets – they do not have an equivalent to accept() and 
> there is no multiplexing of inputs; all writes to the FIFO immediately 
> go to the "listening" file descriptor. So it's almost more like a 
> datagram socket than a stream one, in a sense.
>
> If you want a true socket that's filesystem-based, create a Unix 
> socket by specifying the path via ListenStream, then connect to it 
> using nc -U.
>
>

Yes writing the socket at:

# emailoutput.socket
[Unit]
Description=Send email

[Socket]
ListenStream=%t/emailoutput.socket
Accept=yes

Then things like

echo "Hi There"  | nc -U /run/emailout.socket

work great and an instance of emailoutput at .service is created.

Then the final thing I was trying to do was use that created 
ListenStream that from another unit. e.g.

[Unit]
Description=Simple command

[Service]
ExecStart=/usr/bin/ls /etc/passwd /etc/notexisting
StandardOutput=file:/run/emailoutput.socket
StandardError=file:/run/emailoutput.socket

A single email of Output and Error is generated - that's great - thanks.

No more questions.

Steve.


> On Thu, Sep 5, 2024, 13:38 Steve Traylen <steve.traylen at cern.ch> wrote:
>
>     Was trying to set up a trivial socket and service to process multiple
>     inputs:
>
>     # Socket emailoutput.socket
>     [Unit]
>     Description=Send email via a socket.
>
>     [Socket]
>     Accept=yes
>     ListenFIFO=/run/emailoutput.socket
>
>     # Service emailoutput at .service
>     [Unit]
>     Description=email
>
>     [Service]
>     ExecStart=/usr/bin/mailx -s 'Testing from socket' steve at example.ch
>     StandardInput=socket
>
>
>     Starting the socket always produces: "Unit configured for accepting
>     sockets, but sockets are non-accepting. Refusing"
>
>     Switching the socket to  "ListenStream=127.0.0.1:9999
>     <http://127.0.0.1:9999>" then everything
>     works I can netcat files into the network socket.
>     Is it impossible to to Accept=yes with ListenFIFO?
>
>
>     Motivation for was this i wanted to do perform a systemd-run of a
>     command outputting to that socket to pipe it into mailx.
>
>
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