Linux: Why does Single User mode work on Serial Console but not on the attached Keyboard/Video/Monitor

ipmikeyboard-video-mouselinux

I have a Scientific Linux 6.1 system, which on a Supermicro server which supports IPMI. It's also running with Upstart, which affects how serial consoles work.

My system has a serious problem which requires that I log in to Single User mode to perform some maintenance. I am standing in front of the KVM attached to the server (the VGA console), and I can see all the BIOS and boot messages. The boot sequence goes through the motions, then tells me there is a corrupt filesystem and that's it. I am never presented with a prompt to log into the box, and the screen doesn't say anything about maintenance mode.

I finally connect to the host using the serial console, and I see the following prompt:

* An error occurred during the file system check.
*** Dropping you to a shell; the system will reboot
*** when you leave the shell.
Give root password for maintenance
(or type Control-D to continue):
  1. Why does this prompt for Single User mode appear on the Serial Console only?
  2. More importantly, can I get this to appear on both the Serial Console and on the attached Keyboard/Video/Monitor?

My Kernel commandline is this:

kernel /boot/vmlinuz-2.6.32-131.17.1.el6.x86_64 ro root=UUID=blah-blah-blah  KEYBOARDTYPE=pc KEYTABLE=us console=tty0 crashkernel=auto console=ttyS2,115200n8r

Best Answer

Because init hasnt spawned off multiple TTYs yet (getty, mgetty, etc), so you only have the primary TTY. The primary TTY is the last console= parameter on the kernel command line. All the console parameters get the output, but only the last one will be able to act as input.

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