LVMCREATE_INITRD(8)

NAME
lvmcreate_initrd - create an initial ramdisk to boot with root on a logical volume

SYNOPSIS
lvcmreate_initrd [-i|--iop IOP] [-D|--devfs] [-v|--verbose] [-V|--version] [KernelVersion]

DESCRIPTION
lvmcreate_initrd creates a new compressed initial ramdisk /boot/initrd-lvm-KernelVersion.gz. The initial ramdisk contains all necessary binaries, shared libraries and a linuxrc file to switch to a logical volume based root filesystem. To build an initial ramdisk for a kernel other than the one currently running add the KernelVersion parameter (e.g. lvmcreate_initrd 2.3.25) on the command line.

  OPTIONS

-h, --help
    Print a usage message on standard output and exit.

-i, --iop IOP
    Specify the LVM kernel IOP version if you are using wrapper scripts in /sbin. This is only necessary if you are building an initrd for a kernel other than the current one, and you have tools for multiple IOP versions installed.

-D, --devfs
    Force the use of devfs when building the initrd. lvmcreate_initrd by default probes for devfs by checking for /dev/.devfsd, which is created by devfsd when it is running. This option will force lvmcreate_initrd to do this, when devfsd is not currently running.

-v, --verbose
    Gives verbose runtime information about the creation of the ram disk image.

-V, --version
    Print version number and exit successfully.

The necessary actions to change your system into a "root on logical volume" one are:

Create a small (~20MB) partition which is BIOS reachable to hold the /boot filesystem (if you already have a small partition based root filesystem this can be used instead). If you want to boot standalone from this partition in an emergency, copy all the necessary binaries and libraries to that filesystem as well and create a corresponding /etc/lilo.conf entry. In order to be able to edit lilo.conf when booted standalone, you should move /etc/lilo.conf to /boot/lilo.conf and create a symbolic link to it in /etc. This is not needed if you have a boot/root floppy which contains the LVM binaries and the library.

Create all logical volumes you need (for root, usr, opt etc.), create filesystems in them, mount them and transfer all files from the partition based filesystems into the logical volume based ones.

Set up your /etc/lilo.conf with a boot configuration like:
image = /boot/vmlinuz
initrd = /boot/initrd-lvm-KernelVersion.gz
root = /dev/YourVG/YourRootLV
label = rootonlv
append = 'ramdisk_size=8192'
Replace YourVG and YourRootLV by your actual volume group and root logical volume names. You also need to change the ramdisk size to be at least as large as that reported while lvmcreate_initrd is run. If you have enough memory, it is OK if the ramdisk size in /etc/lilo.conf is larger than what lvmcreate_initrd reports (the memory is freed after booting). Also, your /etc/fstab in the root logical volume should contain entries for the root LV, and the boot partition, along with any other LVs you have configured:
/dev/YourVG/YourRootLV      /     ext2   defaults   0   1
/dev/YourBootPartition      /boot ext2   defaults   0   2
/dev/YourVG/YourUsrLV       /usr  ext2   defaults   0   3
/dev/YourVG/YourOptLV       /opt  ext2   defaults   0   4
etc.
You can use other supported filesystem types as well (e.g. reiserfs) if you have support for those in your kernel. Run lilo, reboot and try...

The partitions containing the former /usr, /opt etc. filesystems can now be used as physical volumes. Use pvcreate(8) to turn them into PVs and then use vgextend(8) to add them to e.g. YourVG.

DIAGNOSTICS
lvcmcreate_initrd returns 0 for success. 1 is returned in all other cases.

SEE ALSO
lilo(8), lilo.conf(5), fstab(5), lvm(8), pvcreate(8), vgextend(8), lvcreate(8), vgcreate(8)

AUTHOR
Heinz Mauelshagen <Linux-LVM@Sistina.com>