Monthly Archives: December 2016

CLI, OS

Rename LVM group in CentOS7

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I recently made the discovery that all my VMs have the same volume group name – the default that is given when CentOS is installed. My OCD got the best of me and I set out to change these names to reflect the hostname. The problem is if you rename the volume group containing the root partition, the system will not boot.

The solution is to run a series of commands to get things updated. Thanks to the centOS forums for the information. In my case I had already made the mistake of renaming the group and ending up with an unbootable system. This is what you have to do to get it working again:

Boot into a Linux rescue shell (from the installer DVD, for example) and activate the volume groups (if not activated by default)

vgchange -ay

Mount the root and boot volumes (replace VG_NAME with name of your volume group and BOOT_PARTITION with the device name of your boot partition, typically sda1)

mount /dev/VG_NAME/root /mnt
mount /dev/BOOT_PARTITION /mnt/boot

Mount necessary system devices into our chroot:

mount --bind /proc /mnt/proc
mount --bind /dev /mnt/dev
mount --bind /sys /mnt/sys

Chroot into our broken system:

chroot /mnt/ /bin/bash

Modify fstab and grub files to reflect new volume group name:

sed -i /etc/fstab -e 's/OLD_VG_NAME/NEW_VG_NAME/g'
sed -i /etc/default/grub -e 's/OLD_VG_NAME/NEW_VG_NAME/g'
sed -i /boot/grub2/grub.cfg -e 's/OLD_VG_NAME/NEW_VG_NAME/g'

Run dracut to modify boot images:

dracut -f

Remove your recovery boot CD and reboot into your newly fixed VM

exit
reboot

If you want to avoid having to boot into a recovery environment, do the following steps on the machine whose VG you want to rename:

Rename the volume group:

vgrename OLD_VG_NAME NEW_VG_VAME

Modify necessary boot files to reflect the new name:

sed -i /etc/fstab -e 's/OLD_VG_NAME/NEW_VG_NAME/g'
sed -i /etc/default/grub -e 's/OLD_VG_NAME/NEW_VG_NAME/g'
sed -i /boot/grub2/grub.cfg -e 
's/OLD_VG_NAME/NEW_VG_NAME/g'

Rebuild boot images:

dracut -f
CLI, OS

Create a RaidZ array with missing drive in FreeNAS

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I came across a need to create a ZFS Raid-Z array with a missing drive. This is easy to do with mdadm but not as easy with ZFS. It is possible, though. The trick is to create an image file with dd, then map that image file as a loopback device. Once that’s done you can treat it as if it were a regular hard drive and add it to the array. Once added to the array you can take the loopback device offline and remove it from the array, then add an actual HDD later.

Create loopback device

Thanks to this site for the information.

First, use dd to create an image file. Change the seek parameter to whatever size disk you wish to emulate.

dd if=/dev/zero of=temp.img bs=1 count=1 seek=1024G

Next, initialize the loopback driver and create the loopback device (md0 in my case)

sudo losetup -a
sudo mdconfig -a -t vnode -f temp.img -u 0

List your loopback devices with the following command to verify your new loopback device:

sudo mdconfig -l

Create array using loopback device

You can now partition and add your loopback device as if it were a regular hard drive. Change volume name, array name, and device names as necessary for your environment.

sudo gpart add -t freebsd-zfs -l <volume name> md0
sudo zpool create <array name> raidz ada7p1 ada8p1 ada9p1 md0p1

Fail & Remove loopback device

Now that our new array is up and running properly we can fail out the loopback device. Make sure to modify the command to use your array name and loopback device/partition number.

sudo zpool offline <array_name> md0p1

Import new array into FreeNAS GUI

To get our new array in freenas we must export the array from the command line, then import it from the GUI.

sudo zpool export <array name>

Once the array has been exported, navigate to the FreeNAS GUI and go to Storage / Volumes / Import Volume.

You should now have your new array minus one drive ready to go in FreeNAS. You can now add a physical HDD when it becomes available (in my case, when it returns from RMA.)

CLI, OS

Install notepadqq on Debian 8 (jessie)

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Notepadqq is a version of notepad++ adapted for Linux. I love notepad++ for its powerful features and also because it’s free. Notepadqq has a ppa configured for easy installation for Ubuntu users, but for everyone else they must resort to compiling it. Fortunately it’s not too complicated. Thanks to linuxbabe for the guidance.

For Debian 8 users this is what you have to do:

sudo apt-get install qt5-qmake libqt5webkit5 libqt5svg5 coreutils libqt5webkit5-dev libqt5svg5-dev qttools5-dev-tools git
git clone https://github.com/notepadqq/notepadqq.git
cd notepadqq
./configure
make
sudo make install

After a bit of time notepadqq will be compiled and installed. That’s it!

If you are running gnome-shell or a derivative (such as cinnamon) then you can get your newly installed program to show up in the menu by pressing alt+f2, hitting r, and then hitting enter. This causes the shell to reload so it will pick up your newly installed program.