A.3. Build the initrd image

The next step is to build the actual ramdisk image, which is described in the following subsections. The important thing to remember is that any program that needs to run from the initrd needs to be copied to the initrd. In addition, any shared libraries that are needed by programs that run from the initrd need to be copied to the initrd as well.

A.3.1. Create a new, blank initrd

Start by creating a new initrd image with an ext2 file system. The following example creates the initrd image at /boot/initrd-evms. You can choose to use a different file name if you wish.

The size of the initrd in the following example is 16 MB. You can make the initrd larger or smaller by adjusting the "count" value. The minimum size needed for all the required EVMS tools and supporting libraries is about 11 MB. If you are installing kernel modules to your initrd (see step 3-H below) or other non-EVMS programs, the size might need to be increased.

dd if=/dev/zero of=/boot/initrd-evms bs=1M count=16
mke2fs -F -m 0 -b 1024 /boot/initrd-evms

A.3.2. Mount the initrd

In order to copy all the required files to the initrd, the initrd must be mounted through a loopback device. To mount the initrd through a loopback device requires that you have loopback support compiled in your kernel (or as a kernel module). See the "Block Devices" menu in the kernel configuration for more information about loopback.

mkdir /mnt/initrd
mount -t ext2 -o loop /boot/initrd-evms /mnt/initrd

A.3.3. Set up the basic directory structure

Use the following commands to create several basic directories that are required on the initrd:

cd /mnt/initrd
mkdir bin dev etc lib proc sbin var
cd var
mkdir lock log

A.3.4. Copy helpful utilities

The script that runs in the initrd requires a few common command-line utilities, which you can create with the following commands:

cd /bin
cp -a bash cat echo expr grep mount sh umount /mnt/initrd/bin
cd /etc
cp fstab /mnt/initrd/etc

A.3.5. Copy supporting libraries

The utilities from the previous step, along with the EVMS tools, require a few common shared libraries. You can create these shared libraries with the following commands:

cd /lib
cp -a ld-* /mnt/initrd/lib
cp -a libc-* libc.* /mnt/initrd/lib
cp -a libdl-* libdl.* /mnt/initrd/lib
cp -a libpthread* /mnt/initrd/lib
cp -a libtermcap* /mnt/initrd/lib

It is possible that some of the utilities (bash in particular) require additional libraries. Use the ldd command to determine if you need additional libraries copied to your initrd. For example, output from the ldd /bin/bash command provides a list similar to the following:

libtermcap.so.2 => /lib/libtermcap.so.2 (0x40020000)
libdl.so.2 => /lib/libdl.so.2 (0x40024000)
libc.so.6 => /lib/libc.so.6 (0x40027000)
/lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x4000000)

All libraries listed by ldd need to be copied to the /lib directory on the initrd.

A.3.6. Copy the EVMS tools

Several EVMS libraries and a couple of executables need to be copied to the initrd. First, you need to locate where the EVMS libraries were installed. By default, these libraries are installed in /lib. If you specified a different prefix or libdir when you configured EVMS, the libraries might be located in a different directory. It is important that these libraries be installed in the same location on the initrd as they are on your real system. For example, if the libraries installed in /lib, the libraries need to be copied to /lib on the initrd; If the libraries are installed in /usr/lib, they need to be copied to /usr/lib on the initrd.

The following example assumes the libraries are installed in /lib. Only the shared libraries (.so) need to be copied. The static versions (.a) are not needed on the initrd.

cd /lib
cp -a libevms*so* /mnt/initrd/lib
cp -a libdlist*so* /mnt/initrd/lib

Next, copy the plug-in libraries to the initrd. The plug-ins are always installed in the evms subdirectory of the directory where libevms is installed.

Not all of the plug-ins need to be copied to the initrd. Several plug-ins are only for interfacing with the file system utilities and are not necessary at boot time. Other plug-ins are only for interfacing with clustering packages, which cannot be started until the regular boot process.

The following is a list of the specific plug-ins that do not need to be installed:

Create and change directory to /lib/evms:

mkdir /mnt/initrd/lib/evms
cd /lib/evms

Copy the contents of the /lib/evms directory, minus the plug-ins listed earlier that do not need to be installed, to /mnt/initrd/lib/evms:

for foo in aix bbr bsd disk dos drivelink gpt lvm md os2 s390 snapshot sparse
  cp -a *$foo* /mnt/initrd/lib/evms

Next, copy the activation program to the initrd. The full user interfaces are not needed, because the only thing the initrd does is activate the volumes. Unlike the EVMS libraries, the exact location of this program in the initrd is not important, so it can simply go in sbin:

cd /sbin
cp evms_activate /mnt/initrd/sbin
cp get_dev_num /mnt/initrd/sbin

Finally, if you have an /etc/evms.conf file installed, you should copy it to the initrd so that EVMS uses the correct options during activation. (However, if you have an /etc/evms.conf file but have never modified it for your system, it should still have all the default values and does not necessarily need to be installed on the initrd.)

cd /etc
cp evms.conf /mnt/initrd/etc

A.3.7. Set up disk devices

The initrd needs to be set up to reflect the disk devices that are on your system. EVMS needs to find the disks in order to activate the volumes.

Before setting up the disk devices on the initrd, determine if you are using devfs. If you are not sure, you can quickly check for the file /dev/.devfsd. If /dev/.devfsd exists, you are running devfs. You can also check your kernel configuration in the "Filesystems" menu. If "/dev file system support" and "Automatically mount at boot" are enabled, you are running devfs.

A.3.7.1. devfs users

Because devfs runs automatically within the initrd, you do not need to manually copy the device files to the initrd. However, devfs does need to be mounted within the initrd for it to work properly. There are two ways to accomplish this:

  • In the kernel configuration, in the "Filesystems" menu, set the "Automatically mount at boot time" option. With this option set, devfs will be automatically mounted on /dev when the initrd is loaded.

  • Manually mount devfs from the linuxrc script before running evms_activate. See Section A.3.9 for more details.

A.3.7.2. devfsd users

EVMS does not require devfs users to run devfsd. However, if you do run devfsd, you also need to run it on the initrd to ensure that all disks and segments are discovered with the same names on both the initrd and the real system. Thus, if you run devfsd, you need to copy the devfsd program and config file to the initrd, as follows:

cd /sbin
cp devfsd /mnt/initrd/sbin
cd /etc
cp devfsd.conf /mnt/initrd/etc

Next, examine the devfsd.conf file (the one you just copied to the ramdisk) with a text editor. First look for a line like this:


Also in the devfsd file, look for a line that begins with RESTORE. This line specifies a directory where devfsd stores changes to the /dev file system. Create this directory in your initrd. For example, if your devfsd.conf file contains the line "RESTORE /dev-state," issue the following commands to prevent error messages from being generated when devfsd starts within the initrd:

cd /mnt/initrd
mkdir dev-state

A.3.7.3. Non-devfs users

Because devfs is not running and mounted within the initrd, you need to manually copy the necessary device node files to the initrd. If you only have IDE or SCSI disks, the following commands should be sufficient. If you specifically know which disks are on your system, you can copy only those device files.

cd /dev
cp -a hd[a-z] /mnt/initrd/dev

In addition to the disk devices, you also need a console device:

cp -a console /mnt/initrd/dev

A.3.8. Copy kernel modules

If you have any kernel modules that need to be loaded in order for EVMS to run, those modules need to be copied to the initrd. In particular, if you build your IDE or SCSI drivers, the Device Mapper or MD/Software-RAID drivers, or any required file systems as modules, they need to be present on the initrd so they can be loaded before you run EVMS and try to mount the root file system.

If you build all of the necessary drivers and file systems statically into the kernel, you can skip this step. Skipping this step is the recommended approach so that you avoid any possible problems that might be caused by required modules missing from the initrd.

When copying the kernel modules, it is probably safest to copy the entire module directory so as not to miss any modules that might be needed on the initrd:

mkdir /mnt/initrd/lib/modules
cd /lib/modules
cp -a x.y.z /mnt/initrd/lib/modules

x.y.z is the version of the kernel that will be running EVMS and the initrd.

In addition, you will need the module-loading utilities, and probably the module configuration file:

cd /sbin
cp modprobe /mnt/initrd/sbin
cd /etc
cp modules.conf /mnt/initrd/etc

A.3.9. Write the linuxrc script

At this point, all of the necessary files, programs, and libraries should be on the initrd. The only thing remaining is the linuxrc script. When the kernel mounts the initrd, it tries to run a script called linuxrc, in the root of the initrd. This script performs all the actions necessary for the initrd, and prepares the root device so that it can be mounted when the initrd exits.

A sample linuxrc script is provided in the doc directory of the EVMS source package. You can use this script as a starting point.

Copy the linuxrc sample to your initrd:

cd /usr/src/evms-2.0.0/doc
cp linuxrc /mnt/initrd

Open the linuxrc sample script in your favorite text editor. The following paragraphs provide a brief explanation of what the linuxrc does at boot time and offer suggestions for modifying the script for your system.

When the linuxrc script completes, the kernel automatically tries to mount the root file system, and the initrd is removed from memory.

A.3.10. Unmount the initrd image

The contents of the initrd should now be complete and you can unmount it.

A.3.11. Compress the initrd image

To conserve space, compress the initrd image:

gzip /boot/initrd-evms