Gentoo LVM2 installation
This guide is based on an example with two SATA hard disks. It means that you
will more than likely need to change the drive, partition names and partition
sizes to match your own setup and needs.
This document is not intended to be an LVM2 tutorial. It serves as a
supplement to the Gentoo installation procedure as described in the Handbook, Part 1. Make
sure you read the Gentoo Installation Manual before you start
your installation process.
For a complete LVM HOWTO point your browser to
If you do a fresh install of Gentoo, you will need to use a bootable CD with
LVM2 support such as a Gentoo Installation CD. You can find the Installation CDs
for an x86 architecture on our mirrors
under /releases/x86/current/installcd. Other architectures might be
supported as well.
If you install LVM2 on a currently running system with some spare hard disk
space, you will need to enable the LVM2 module (dm-mod) in the
kernel. This module is available in gentoo-sources. Compiling
your kernel and getting LVM2 to work is covered later in this guide.
Our example system has two SATA hard disks and will be partitioned as follows:
- /dev/sda1 -- /boot
- /dev/sda2 -- (swap)
- /dev/sda3 -- /
- /dev/sda4 -- Will be used by LVM2
- /dev/sdb1 -- Will be used by LVM2
Pay attention to the partition names as it is easy to confuse the a's and b's,
and the partition numbers. One false move could wipe out the wrong partition.
You have been warned!
OK, time to start...
Follow the handbook, but with the following amendments to chapter 4.
Preparing the Disks:
Use fdisk as described in the handbook, but use the partition scheme
mentioned above as an example. It is only an example, adapt it to your
Create a small physical /boot partition (sda1). In this example,
/boot will be not managed by LVM2. This partition will contain
your bootloader and your kernel(s). A 64MB partition should be well enough for
quite a few kernel generations.
Create a swap partition (sda2).
Create a / (root) partition (sda3). If you are interested in trying to put your
root partition under LVM management (which we do not recommend), see the
resources section at the end of this guide for a link to a mini-howto on how to
do this. The size of the root partition need not be large if you will keep
/opt /usr /home /var and /tmp in an LVM2 Volume Group
(vg). In this case, 1GB should be sufficient. Note however that, if you have
/usr or /var in an LVM2 volume group, you will need to
boot the system with an initramfs.
It is not recommended to put the following directories in an
LVM2 partition: /etc, /lib, /mnt,
/proc, /sbin, /dev, and
/root. This way, you would still be able to log into your system
(crippled, but still somewhat usable, as root) if something goes terribly wrong.
Also exclude /usr and /var from LVM2 if you do not
want to boot with an initramfs.
Assuming the /boot, swap and root partitions do not use the whole
physical disk, create a fourth partition on this disk and set it to type 8e
(Linux LVM). If you have more physical drives you would like to use with LVM,
create one partition on each and give them the same type (8e).
Considering the huge size of current disks, you might consider splitting your
hard disks into smaller partitions instead of creating a big partition that
will be added to an LVM2 volume group in one block. LVM2 makes it easy to
extend your volumes after all. This leaves you some unallocated partitions you
might need to use outside of an LVM2 group. In short, don't use your disk space
until you know you need it. As an example, one contributor had split his
160 Gb hard disk into 8 partitions of 20 Gb each.
Create the filesystems on /dev/sda1 and /dev/sda3,
and create and activate the swap on /dev/sda2 as described in the
Start the lvm service.
Code Listing 2.1: Starting the lvm service
# rc-config start lvm
It is recommended to add the lvm service to the boot runlevel. This way LVM2
will be activated each time the system boots.
Code Listing 2.2: Adding lvm to the boot runlevel
# rc-config add lvm boot
Before scanning and activating LVM, you might want to edit
/etc/lvm/lvm.conf to exclude some devices. By default, LVM2 will
scan all devices, even your CDROM which can generate error messages. In the
following example, the line that allows scanning of all devices is replaced by
one that rejects every device but our two SATA disks.
Code Listing 2.3: Activating LVM
# nano -w /etc/lvm/lvm.conf
filter = [ "a/.*/" ]
filter = [ "a|/dev/sd[ab]|", "r/.*/" ]
Reading all physical volumes. This may take a while...
No volume groups found
# vgchange -a y
Prepare the partitions.
Code Listing 2.4: Preparing the partitions
# pvcreate /dev/sda4 /dev/sdb1
No physical volume label read from /dev/sda4
Physical volume "/dev/sda4" successfully created
No physical volume label read from /dev/sdb1
Physical volume "/dev/sdb1" successfully created
Setup a volume group. A volume group is the result of combining several
physical units into a single logical device.
In our example, /dev/sda1, /dev/sda2 and
/dev/sda3 are the /boot, swap and root partitions so
we need to combine /dev/sda4 and /dev/sdb1. It can be
done with a single command, but, as an example, we will create our volume group
and extend it.
Code Listing 2.5: Creating and extending a volume group
# vgcreate vg /dev/sda4
/etc/lvm/backup: fsync failed: Invalid argument
Volume group "vg" successfully created
# vgextend vg /dev/sdb1
/etc/lvm/backup: fsync failed: Invalid argument
Volume group "vg" successfully extended
Create the logical volumes. Logical volumes are the equivalent of partitions
you would create using fdisk in a non LVM2 environment. In our example, we
create the following partitions:
Since we are going to use LVM2, we should not worry too much about partition
sizes because they can always be expanded as needed.
As Terje Kvernes commented, it is easier to increase the size of a partition
then to shrink it. You might therefore want to start with smaller partitions
and increase their size as needed.
Code Listing 2.6: Creating and extending logical volumes
# lvcreate -L10G -nusr vg
Logical volume "usr" created
# lvcreate -L5G -nhome vg
# lvcreate -L5G -nopt vg
# lvcreate -L10G -nvar vg
# lvcreate -L2G -ntmp vg
# lvextend -L+5G /dev/vg/home
Create filesystems on the logical volumes the same way you would on a regular
partition. We use ext3 on the logical volumes but any filesystem of your
choice will work:
Code Listing 2.7: Creating the filesystems
# mke2fs -j /dev/vg/usr
# mke2fs -j /dev/vg/home
# mke2fs -j /dev/vg/opt
# mke2fs -j /dev/vg/var
# mke2fs -j /dev/vg/tmp
Mount your partitions as described in the handbook and mount your LVM2 logical
volumes as if they were partitions. Replace the usual /dev/sdxx
Code Listing 2.8: Mounting your logical volumes
# mkdir /mnt/gentoo/usr
# mount /dev/vg/usr /mnt/gentoo/usr
# mkdir /mnt/gentoo/home
# mount /dev/vg/home /mnt/gentoo/home
# mkdir /mnt/gentoo/opt
# mount /dev/vg/opt /mnt/gentoo/opt
# mkdir /mnt/gentoo/var
# mount /dev/vg/var /mnt/gentoo/var
# mkdir /mnt/gentoo/tmp
# mount /dev/vg/tmp /mnt/gentoo/tmp
The rest of the installation handbook is mostly unchanged so we shall not
walk you through it again except to point out differences.
When configuring your kernel, make sure to configure your kernel to
support LVM2. Select the LVM2 module as follows:
Code Listing 2.9: Selecting the LVM2 module in the Linux kernel
Device Drivers --->
Multiple devices driver support (RAID and LVM) --->
[*] Multiple devices driver support (RAID and LVM)
< > RAID support
<M> Device mapper support
The compiled module is called dm-mod.ko
Also build an initramfs if you have /usr or /var on an
LVM-based partition. Don't forget to edit your boot loader to boot the system
with the initramfs and add in dolvm as a boot parameter.
Code Listing 2.10: Building an initramfs
# emerge genkernel
# genkernel --lvm --install initramfs
# nano -w /boot/grub/grub.conf
title Gentoo Linux
kernel /kernel-3.2.2-gentoo-r5 root=/dev/sda1 dolvm
Now, install the lvm2 package.
Make sure your /usr/src/linux link points to the kernel sources you
are using because the lvm2 ebuild depends on the device-mapper ebuild which
will check the presence of a required source file under
Code Listing 2.11: Emerging the LVM2 package
# emerge lvm2
Edit /etc/lvm/lvm.conf as described earlier. The file you previously edited is part of
your installation environment and will disappear after the next reboot. This
time, you edit the real one inside your new Gentoo install.
When editing your /etc/fstab file, follow the handbook and add
your LVM2 logical volumes as needed. Again, here are a few lines needed for
Code Listing 2.12: Extract of /etc/fstab
/dev/sda1 /boot ext3 noauto,noatime 1 2
/dev/sda2 none swap sw 0 0
/dev/sda3 / ext3 noatime 0 1
# Logical volumes
/dev/vg/usr /usr ext3 noatime 0 2
/dev/vg/home /home ext3 noatime 0 2
/dev/vg/opt /opt ext3 noatime 0 2
/dev/vg/var /var ext3 noatime 0 2
/dev/vg/tmp /tmp ext3 noatime 0 2
When you reach the end of the installation part of the handbook, don't forget
to umount all your LVM2 logical volumes as well and for a good measure run the
following command before you reboot:
Code Listing 2.13: Shutting down LVM2
# vgchange -a n
Restart your machine and all partitions should be visible and mounted.
Continuing After a Reboot
If you have interrupted the Gentoo installation at one point and want to
continue, you need to create the volume device nodes first:
Code Listing 3.1: Reactivating the volumes
# vgscan --mknodes
Installation CDs with less recent tools might need to reactivate the volumes
Code Listing 3.2: Reactivating the volumes
# vgchange -a n
# vgexport -a
# vgimport -a
# vgchange -a y
Thanks Thilo Bangert and Terje Kvernes for their help and comments on
The contents of this document, unless otherwise expressly stated, are licensed under the CC-BY-SA-2.5 license. The Gentoo Name and Logo Usage Guidelines apply.