[SOLVED] how to prevent Xorg from clearing boot messages in scrollback

Question

I have an updated Arch install with MATE and LightDM. LightDM autologin is enabled, so I normally boot directly to my desktop. I like seeing the messages that flash by during boot, so I deleted the word "quiet" from the linux line in my grub.cfg. Because I want all the messages to still be there after flashing by (in case I want to scroll through them later), I followed the advice here https://wiki.archlinux.org/index.php/Di … t_messages and I also increased the scrollback buffer and enabled early KMS start.
Despite all the above, I can only scroll back to the beginning of the boot messages if I boot into non-graphical mode (e.g., by adding "systemd.unit=multi-user.target" to GRUB command line). If I allow a normal boot to my destkop and THEN go to non-graphical mode with "sudo systemctl isolate multi-user.target" to look at the boot messages, I notice that I cannot scroll back very far at all--most of the messages that flashed by during boot are gone. Therefore, it seems to me that either lightDM or Xorg is resetting the scrollback buffer and erasing all but the last few boot messages.
So, how do I tell LightDM or Xorg (whichever one is the culprit) *not* to clear the scrollback buffer, so that when I get out of graphical mode and into non-graphical mode the boot messages are all still there?
Last edited by bdantas (2014-08-01 14:19:06)

Answer 1

Since the answer to my original question seems to be "it is not possible," I will make this my last post to prevent the thread from going off-topic.
I came up with a simple workaround that (almost) recreates the old /var/boot/log:
1) put "quiet" on grub2's kernel command line so that only* [FAIL] messages show up, so that I don't have to deal with the scrollback buffer
2) create a startup script with the following contents (script or at least the setterm command must run as root because the setterm command needs to be able to read from /dev/vcs1):
#!/bin/bash
# this script will dump the text of tty1 to /var/log/boot, with same formatting as on the screen
export TERM=xterm
setterm -dump 1 -file /var/log/boot
exit 0
* Unfortunately, even in quiet mode grub2 starts printing all the boot status messages to screen once it encounters a [FAIL]. Therefore, if the [FAIL] occurs early enough in the boot process, the beginning of the messages will scroll off the screen and the workaround won't work. I spun off my two questions related to this nuisance into their own threads:
a) How to make grub2 actually only print [FAIL] messages during boot? https://bbs.archlinux.org/viewtopic.php?id=184702
b) How to print the contents of console's scrollback buffer to a file? https://bbs.archlinux.org/viewtopic.php … 9#p1439359
I hope I can figure out how to do one of the above, because then the workaround would be perfect.
Thanks for the help, guys!
Last edited by bdantas (2014-08-15 02:16:38)