Index ¦ Archives ¦ RSS

GRUB2 vs. RAID1, cfdisk and serial console

Estimated read time: 2 minutes

Since the Frugalware 1.7 release is near, and it uses GRUB2 by default, I created a virtual machine, that is similar to the one we use under, which hosts this blog as well.

The relevant details:

  • it has two RAID1 arrays with ext3:

$ mount|grep /md
/dev/md126 on / type ext3 (rw,relatime,errors=continue,barrier=1,data=ordered)
/dev/md127 on /home/ftp/pub type ext3 (rw,relatime,errors=continue,barrier=1,data=ordered)
  • the partition tables are created by cfdisk:

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1              63  1465144064   732572001   fd  Linux raid autodetect
  • the machine has a serial console configured:

# cat /proc/cmdline
root=/dev/disk/by-uuid/7e41c95d-cd73-4043-b0ba-4797af6ddeff ro vga=normal nomodeset console=ttyS1,115200

Now the question is how does this config deal with the GRUB2 upgrade. First, don’t miss the official upgrade howto, it covers most cases. What I want to detail here is how did I avoid starting from scratch and creating a proper partition table using fdisk.

Here are the steps I needed:

  • Backup. Yes, I did screw up for the first time, so it’s really needed.

  • Resize parts of the / RAID1 (/dev/sda1 and /dev/sdb1) with gparted livecd (resizing ext3 from cmdline parted didn’t work for me).

  • mdadm re-creation as described in the upgrade howto, from fw install cd, so you’ll have the required 1.0 metadata.

  • Reinstall GRUB1 to sda and sdb, since the physical location of GRUB1’s stage* changed.

  • Boot back to 1.6, run pacman-g2 -Syu, and grub-install — again, see the upgrade howto for details.

  • Now given that serial console needs a custom GRUB config and kernel parameters, you need to modify GRUB2’s /etc/default/grub. Here is my diff:

    /etc/default# diff -u grub.orig grub
    --- grub.orig   2012-07-19 01:57:20.000000000 +0200
    +++ grub        2012-07-29 14:45:50.000000000 +0200
    @@ -1,11 +1,12 @@
     GRUB_DISTRIBUTOR="Frugalware 1.6"
    -GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
    +GRUB_CMDLINE_LINUX_DEFAULT="vga=normal nomodeset plymouth.enable=0 console=ttyS0,115200"
    +GRUB_SERIAL_COMMAND="serial --speed=115200 --port=0x3f8"

    (Refer to this post if you don’t know the needed port number.)

  • Finally run grub-mkconfig to create the real config from the just modified default settings.

  • Reboot, and GRUB2, the boot process and the login prompt should be accessible over the serial console again.

© Miklos Vajna. Built using Pelican. Theme by Giulio Fidente on github.