ID #1308

Analyze boot problems

Produktlogo UCS UCS 4 
Problem:

A system does not boot and seems to freeze at bootsplash.

Solution:

It is possbile to edit the boot options for the UCS system within GRUB. You can disable the splashscreen and raise the loglevel - by that you can see what happens when the system freezes:

1. Press button "e" in GRUB bootloader
2. Find the follwing line:
linux ... /vmlinuz-... ... ro quiet loglevel=0 rootdelay=5 splash3. Edit the line: Remove "quiet" and change "slpash" to "nosplash" - also set "loglevel" to 5
the line should now look like this:
linux ... /vmlinuz-... ... ro loglevel=5 nosplash4. Boot by pressing F10

These changes are temporaliy and are re-set at next boot. You can make that change permanent by booting into the working UCS system, logging in as root, and setting the following UCR variables:

ucr set grub/bootsplash=nosplash grub/quiet=no grub/loglevel=5

Advanced options:

The default text console only has 80 columns and 25 rows, so some important output might scroll of. You can configure a serial console to capture that output.

  • Many USB serial converters don't work reliably.
  • Many high-end servers support serial console re-direction over network, for example over IPMI. See How to do remote server administration over IPMI
  • Many virtual machines provide virtual serial interfaces, which can also be used:
    For Qemu/KVM/Xen-HVM
    adding a <console/> or <serial/> element to the VM definition and use ttyS0
    Xen-PV
    Use hvc0 as the serial device name .
    The console can be accessed by running virsh console "$VM". As an alternative the output can be logged into a file on the host by using something like <serial type='file'><source path='/tmp/$VM.log' append='on'/></serial> in the VM definition. The virsh conole-command must be kept running as otherwise all output is lost.
  1. Configuring the boot-loader GRUB to use a serial console is described in SDB 1367.
  2. The Linux kernel can also be instructed to redirect its output to a serial console:
    ucr set grub/append='console=tty0 console=ttyS0,115200,8,N,1' This makes the serial console the default console (/dev/console), as ttyS0 is given last. By moving console=tty0 to the end, the VGA console will remain the main console.
  3. Start a login getty on the serial console:
    sed -i -re '/^#?T0:/s/#//' /etc/inittab

Tags: console, grub, Linux, serial, UCS 4

Related entries:

Last update: 2017-02-10 14:29
Author: Tim Petersen
Revision: 1.3

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