[systemd-devel] Output boot status, etc to LCD display

John Obaterspok john.obaterspok at gmail.com
Wed Aug 13 12:50:54 PDT 2014

2014-08-13 21:26 GMT+02:00 Lennart Poettering <lennart at poettering.net>:
> You could probably script something using socat's "PTY"
> transport. i.e. a script that uses socat to allocate a pty, then reads
> strings from it, and translates this to the format you need it in...

Wouldn't that make it pretty hard to get the first messages that are
spit out? (from the first "Welcome to Fedora 20 (Heisenbug)!"
Or perhaps you ment that I could read from journal afterwards?

> If I were you I'd hack that up in C though rather than in shell...

Currently I just use the script to show the IP after boot is done and
later just turn the display off :)

> Note that you need to think about buffer with this. Because 1200 baud is
> really slow, and you cannot really slow down journald to that, because
> journald will actually write synchronously to the TTYPath= you tell
> it. So you'd probably have to add something that is smart enough to read
> from the pty as quickly as possible and only updates the most recent to
> lines into your serial display...
> Otherwise your boot would be slowed down to a crawl...

I bet, my goal was just to show the green/red messages during boot
(stripped to 20 chars wide)

[  OK  ] Reached target Remote File Systems.
[  OK  ] Listening on Delayed Shutdown Socket.
[  OK  ] Listening on /dev/initctl Compatibility Named Pipe.
[  OK  ] Reached target Paths.
[  OK  ] Reached target Encrypted Volumes.

information that is printed during boot, and after boot is done I
wanted to have current IP on row 1 and perhaps something like name of
latest failed service on row 2.

-- john

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