On Sunday, August 4, 2024 5:45:07 PM EDT nerdopolis wrote: > Hi > > I have been doing some testing on VT-less desktops. I brought up an issue with > how systemd was not logging to /dev/console because isatty() was failing (in a > thread last month which I kind of bungled by accidentally sending the first > message with rich text enabled by accident) I solved that issue though. As > disabling the VT console causes the default console to /dev/ttyS0 and the > isatty() calls on it were returning false. > > I have found out that this issue actually already has an existing solution in > the ttynull driver. After enabling it, and then adding console=ttynull to the > kernel command line, this allows isatty() to succeed on VT-less systems, and > now systemd is able to correctly log its status messages to the kernel console > on VT-less systems, without needing anything connected to /dev/ttyS0 > > However I have two questions: > > 1. Is there a build option to make it prioritize /dev/ttynull over /dev/ttyS0 ? > > It would probably be neeed so that distributions don't have to worry about > the logistics of adding that to everyone's GRUB_CMDLINE_LINUX_DEFAULT come > the eventual day the decide to go VT-less during its upgrade process. > > 2. Is there a good way for the userspace to know that /dev/ttynull is primary? > Hi So I think I figured this part out, while ttynull doesn't make its way into the /sys/devices/virtual/tty/console/active file, it is reported in /proc/consoles so I will read from there, seems like the primary console is always the first line, so this part is solved Thanks > "ttynull" doesn't seem to appear in /sys/devices/virtual/tty/console/active > when it is active. Which seems like it could make sense, (as in a check if > it is empty) however if I boot with "console=ttyS0 console=ttynull", "ttyS0" > appears in the file, but if I boot with say "console=tty0 console=ttyS0", > they both appear in the file. It would be nice if in the first case it would > report "ttyS0 ttynull". > > With Plymouth, when the primary console is /dev/ttyS0 instead of /dev/tty0 > it defaults to serial logging instead of showing a graphical splash, so now > if you want a graphical splash on a VT-less system, you have to also specify > "plymouth.graphical" on the kernel command line. If it could see "ttynull" > in the end of the file, distributions that go VT-less can also just enable > "ttynull" as the default console, and Plymouth could use that to > differentiate between VT-less desktop systems, or systems that actually want > serial logging, so they don't have to change GRUB_CMDLINE_LINUX_DEFAULT. > > Thanks > > > > >
