On Mon, Feb 13, 2023 at 11:12 AM Giuseppe Sacco <giuseppe@xxxxxxxxx> wrote:
Hello,
I am working on hylafax, a program for sending and receiving faxes, and I
am facing a problem when it should wait for a device that is not in /dev/
but in /dev/pts/. It seems that udev events only cover device creation in
/dev/ and are not fired when the device appear in /dev/pts.
Pseudoterminals are not actually "devices" – they don't exist in /dev or /sys, only in their own separate virtual filesystem (/dev/pts is not part of /dev), so there are no kernel uevents (and therefore no udev events) for the creation of a pty.
I'm not entirely sure whether it even makes sense for a .service unit to wait for a specific pty? I mean, the entire design of ptys is that they're assigned on a first-come basis and there's no way for a process to claim a specific pty for itself, so there's no way for faxgetty@.service to be sure that pty/0 is your fax thing and not e.g. someone's xterm or an incoming SSH connection.
What is supposed to be creating /dev/pts/0 in your case? It might be simplest to have the same software directly start faxgetty@<ptyname>.service as well.
Mantas Mikulėnas
