If the system uses the ext3 file system, a SCSI controller, or labels to reference partitions in /etc/fstab, an initial RAM disk is needed. The initial RAM disk allows a modular kernel to have access to modules that it might need to boot from before the kernel has access to the device where the modules normally reside.

On architectures other than IBM eServer iSeries, the initial RAM disk can be created with the mkinitrd command. However, this step is performed automatically if the kernel and its associated packages are installed or upgraded from the RPM packages distributed by Red Hat; in such cases, you do not need to create the initial RAM disk manually. To verify that an initial RAM disk already exists, use the command ls -l /boot to make sure the initrd-<version>.img file was created (the version should match the version of the kernel just installed).

On iSeries systems, the initial RAM disk file and vmlinux file are combined into one file, which is created with the addRamDisk command. This step is performed automatically if the kernel and its associated packages are installed or upgraded from the RPM packages distributed by Red Hat, Inc.; thus, it does not need to be executed manually. To verify that it was created, use the command ls -l /boot to make sure the /boot/vmlinitrd-<kernel-version> file already exists (the <kernel-version> should match the version of the kernel just installed).

The next step is to verify that the boot loader has been configured to boot the new kernel. Refer to Section 39.6, “Verifying the Boot Loader” for details.