GRUB2 vs. RAID1, cfdisk and serial console

Posted on: Sun 29 July 2012

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 genesis.frugalware.org, 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_DEFAULT=0
 GRUB_TIMEOUT=5
 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_CMDLINE_LINUX=""
 GRUB_PRELOAD_MODULES=""
-GRUB_TERMINAL_INPUT=console
-GRUB_TERMINAL_OUTPUT=gfxterm
+GRUB_TERMINAL_INPUT=serial
+GRUB_SERIAL_COMMAND="serial --speed=115200 --port=0x3f8"
+GRUB_TERMINAL_OUTPUT=serial
 #GRUB_GFXPAYLOAD_LINUX=keep
 GRUB_GFXMODE=auto
 #GRUB_DISABLE_LINUX_UUID=true

(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.

Category: frugalware – Tags: en