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You’re trying to set up MySQL database replication and despite having correctly set your server-id on the master and slave you keep seeing the following message in the slave server error log: Misconfigured master - server id was not set.

Solution

Bug #3829 states that you can not set the server-id using the SET GLOBAL command.

But I didn’t do that, I set it in my my.cnf and then reloaded MySQL. Whatevs, nerdz.

After much mucking around this morning I realised that reloading MySQL is roughly equivalent to using the SET GLOBAL command. If I think long and hard enough I suppose that makes sense. So…
service mysqld stop
service mysqld start

A few seconds outage on the production server, but now we’re in business.

Problem:

My computer only has 20GB of disk space. I just have 1 partition. I want to add another disk (40GB). I don’t want to add another partition (and I really don’t want to reinstall the whole system), I want to increase the size of the root partition to 60GB. i.e. I want the root partition to span across two physical disks.

Solution:

1. Add new physical disk. Boot.
2. # pvscan

   This will show you the current physical volumes.

3. # fdisk /dev/sdb

   Add the disk to your machine as a primary partition. Partition type: “8e (LVM)”. Obviously /dev/sdb may be different on your system.

4. # pvcreate /dev/sdb1

   This creates a new physical LVM volume on our new disk.

5. # vgextend VolGroup00 /dev/sdb1

   Add our new physical volume to the volume group: VolGroup00. Again, this group name may by different for you, but this is what Redhat & CentOS assigns by default when you install your system.

6. # pvscan

   You should see the new physical volume assigned to VolGroup00.

7. # lvextend -L+40G /dev/VolGroup00/LogVol00

   This increases the size of the logical volume our root partition resides in. Change the -L flag as appropriate.

We’ve just added 40GB to the logical volume used by the root partition. Sweet as. Now we need to resize the file system to utilize the additional space.

8. Reboot into rescue mode using your CentOS CDROM.

   From memory this involves typing linux rescue as your boot option.

9. When prompted, skip the mounting of system partitions.
10. # lvm vgchange -a y

    This command makes your LVM volumes accessible.

11. # e2fsck -f /dev/VolGroup00/LogVol00

    Run a file system check, the -f flag seems necessary. No idea what we do if the returns an error?

12. # resize2fs /dev/VolGroup00/LogVol00

    Without any parameters resize2fs will just increase the file system to the max space available.

Reboot and your root partition is now 40GB lager, spanning multiple disks. Yay.