MortenCB's blog

I am using CentOS 5 for one of my servers, and use raid1 and md for
the mirroring between two drives.

Then one of the drives fail (which they eventually will), here is how
you fix it:

I have taken info from these pages for this blog post:
http://www.howtoforge.com/replacing_hard_disks_in_a_raid1_array
http://blog.mydream.com.hk/howto/linux/howto-reinstall-grub-in-rescue-mode-wh…

In this example I have two hard drives, /dev/sda and /dev/sdb, with
the partitions /dev/sda1 and /dev/sda2 as well as /dev/sdb1 and
/dev/sdb2.
/dev/sda1 and /dev/sdb1 make up the RAID1 array /dev/md0.
/dev/sda2 and /dev/sdb2 make up the RAID1 array /dev/md1.
/dev/sda1 + /dev/sdb1 = /dev/md0
/dev/sda2 + /dev/sdb2 = /dev/md1
/dev/sdb has failed, and we want to replace it.

First of all: ‘cat /proc/mdstat’ is your friend – it will show you the
status of your raid during the whole process.

In the output from ‘cat /proc/mdstat’ you will see an (F) behind a
failed device, or it will be missing alltogether.

First, fail and remove the failed device(s):
mdadm –manage /dev/md0 –fail /dev/sdb1
mdadm –manage /dev/md0 –remove /dev/sdb1
Repeat for other MD-devices containing sdb-parts.
Now the output from ‘cat /proc/mdstat’ should only contain parts from sda.

Power down, change the drive, and turn it back on.

To make the same partitions on sdb as you have on sda, do this:
sfdisk -d /dev/sda | sfdisk /dev/sdb

‘fdisk -l’ should now show the same partitions on sda and sdb.

Next, add the proper parts from sdb to the relevant md-device. So if
md0 contains sda1, do this:
mdadm –manage /dev/md0 –add /dev/sdb1
Repeat for all md-devices so you have the same parts from sda and sdb
in all of them.
Check with ‘cat /proc/mdstat’.

Let is sync back up (check with ‘watch -n 10 cat /proc/mdstat’ until
it finishes).

Now, fix grub:
grub
grub>root (hd0,0)
grub>setup (hd0)

If you’re unlucky and can’t’ boot because the wrong device is first
(trying to boot from the clean/new hard drive), follow these steps:

First boot into a live cd with your os.
Then activate the RAID:
1) mkdir /etc/mdadm
2) mdadm –examine –scan > /etc/mdadm/mdadm.conf
3) mdadm -A –scan

Then reinstall grub. In this example, you have /boot on md0 and / on md1:
1) mkdir /mnt/sysimage
2) mount /dev/md1 /mnt/sysimage
3) mount -o bind /dev /mnt/sysimage/dev
4) mount -o bind /proc /mnt/sysimage/proc
5) chroot /mnt/sysimage /bin/bash
6) mount /dev/md0 /boot
Then fix grub (same as above):
grub
grub>root (hd0,0)
grub>setup (hd0)

Voila, you have a working raid again with grub managing to boot your system 🙂

If you want to change the volume in Ubuntu 11.10 it seems that amixer
is kind of bugged when it comes to toggle (mute/unmute). When
toggling Master, it also mutes all the separate groups (Front,
headphone, PCM and so on), but when toggled again it only unmutes
Master, which leaves the rest muted…

I came across a nice workaround that i wanted to share. The solution
was written by Jim Hunziker on this page:
http://askubuntu.com/a/71551/42842

1) Make a volumetoggle.sh with the following content:

#!/bin/bash CURRENT_STATE=`amixer get Master | egrep 'Playback.*?[o' | egrep -o '[o.+]'|head -n 1`if [[ $CURRENT_STATE == '[on]' ]]; then    amixer set Master muteelse   amixer set Master unmute   amixer set Front unmute   amixer set Headphone unmute   amixer set PCM unmutefi

2) chmod u+x volumetoggle.sh

3) Bind it to some key (f.ex. XF86AudioMute) to run volumetoggle.sh

Voila.

I wanted to cut out two bits from an avi-file and then join them to
get one small file from a large file. I thought using ffmpeg would be
easy for this, but it turns out it might have a but with avi/wmv so I
ended up using mencoder instead.

The original try I did with ffmpeg was:
ffmpeg –ss 00:05:52 -t 00:00:11 -i bigfile.avi small_clip.avi
It looks like it wants to do what I want, since it makes a file where
the first 11 seconds are the ones I want, but then the sound
disappears and all of the rest of bigfile.avi is there (the video at
least).

I could not find any solution for this on the interwebs, so I ended up
trying mencoder which worked:
mencoder -oac copy -ovc copy -ss 00:05:52 -endPos 00:00:11 bigfile.avi
-o small_clip.avi
¨
I repeated the above for all the clips from bigfile.avi and then put
them together:
mencoder -oac copy -ovs copy -idx -o joined_clip.avi small_clip1.avi
small_clip2.avi and so on