Socat Terminates After Connection Close

Socat terminates after connection close

You can limit the number of children with the max-children option:

LISTEN option group, options specific to listening sockets

max-children=
Limits the number of concurrent child processes [int].
Default is no limit.

With this you can limit the number of clients that can interact with the PTY to one, but won't prevent others from connecting. Others will simply queue until the first connection is closed. If you want to prevent that, I'd suggest to just wrap the socat call in a while true; do ..; done loop:

while true; do
  socat PTY,link=/dev/ttyV1,echo=0,raw,unlink-close=0 TCP-LISTEN:11313,forever,reuseaddr
done

Socat not closing tcp connection

If there is no data to send or receive on a socket and you cut the underlying connection neither side is aware until it attempts to send data. Normally, that would be application level data, but at the protocol level you can enable TCP keep alives to emulate flowing data whenever there is no real data.

According to the socat manpage you could try something like:

socat -d -d -d PTY,link=/dev/ttyFOOBAR,echo=0,raw,unlink-close=0 TCP-LISTEN:7000,forever,reuseaddr,keepalive,keepidle=10,keepintvl=10,keepcnt=2

(keepalive actually looks like the essential option but it is unclear what the defaults will be for the tuning options if unset.)

socat device files not removed when interface is closed

From socat's OPTIONS documentation:

-t < timeout >:

When one channel has reached EOF, the write part of the other channel
is shut down. Then, socat waits seconds before
terminating. Default is 0.5 seconds. This timeout only applies to
addresses where write and read part can be closed independently. When
during the timeout interval the read part gives EOF, socat terminates
without awaiting the timeout.

You need to set the timeout as 0.

Socat hangs when piping stdin to tcp server

Turns out it was a combination of things.

1. The version of socat I was using (1.7.3.3) has a bug when using certain options. See https://bugs.launchpad.net/ubuntu/+source/socat/+bug/1883957 for more info.
2. The tty options in my terminal were atypical somehow. By using "stty sane", and then adding -brkint, I got the entire thing working with stdin.

My final solution uses socat version 1.7.4.3, and looks like this:

stty sane

stty -brkint -icanon && socat -,echo=0 tcp:localhost:8088

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