On Friday, July 12, 2024 8:59:58 AM EDT Greg KH wrote: > On Fri, Jul 12, 2024 at 08:52:15AM -0400, nerdopolis wrote: > > Hi > > > > Background:-------------------------------------------------------------------- > > This issue becomes evident on VT-less kernels. As when there is no /dev/tty0 > > device, the console defaults to being /dev/ttyS0 instead. Although this can > > also be replicated if booting a standard kernel with 'console=ttyS0' and ensure > > nothing is plugged into /dev/ttyS0. > > > > This issue prevents systemd from logging to the console. > > systemd when logging to /dev/console, long story short it calls isatty() on > > /dev/console, and when /dev/console is actually /dev/ttyS0, and nothing is > > connected to /dev/ttyS0, isatty() fails on /dev/console due to an input/output > > error, causing systemd to not log the console output, because it rejects > > /dev/console as not being a terminal. > > > > > > This is noticed on a VT-less system with Plymouth. Plymouth calls the TIOCCONS > > ioctl on a pty device it requests, to redirect console output, and in newer > > versions, it displays the console logs on its own without the assistance of a > > VT. > > > > This part of it works, Plymouth is able to 'see' what gets written to > > /dev/console, log output from processes that write to /dev/console directly > > (for example 'echo hi > /dev/console") do appear in plymouth's > > /var/log/boot.log, it is just that systemd is not writing to /dev/console > > because isatty() fails to report /dev/console as a tty device. > > > > The alternate fix in for systemds https://github.com/systemd/systemd/pull/33690[1] > > is believed to be that when TIOCCONS is called on a PTY, or another terminal > > device, that trying to call TCGETS on /dev/console should no longer result > > in an error. > > > > > > Replicating the issue:--------------------------------------------------------- > > > > This program replicates it: > > ------------------------------------------------------------------------------- > > #include <stdio.h> > > #include <fcntl.h> > > #include <unistd.h> > > #include <errno.h> > > #include <string.h> > > > > int main(void) > > { > > int fd; > > > > if (getuid() != 0) { > > printf("Must be root\n"); > > return 1; > > } > > > > fd = open ("/dev/console", O_RDONLY); > > if (!isatty(fd)) { > > printf("err on /dev/console: %s\n", strerror(errno)); > > } > > return 0; > > } > > ------------------------------------------------------------------------------- > > > > When the kernel console is /dev/ttyS0 and /dev/ttySO has no device connected, > > it prints "err on /dev/console: Input/output error" > > > > When I strace it, the relevant line is: > > ioctl(3</dev/console<char 5:1>>, TCGETS, 0x7f...) = -1 EIO (Input/output error) > > Do you have a proposed kernel change for this that solves this for your > tests here? > > thanks, > > greg k-h > Hi Sorry if this is a duplicate, I accidentally had rich text sending turned on, and did not realize until too late. Anyway, to answer the question, unfortunately I have been unable to come up with a fix on my own Thanks
