A prerequisite of installing the MRG Realtime kernel is that the user or administrator first perform a fresh installation of Red Hat Enterprise Linux 5.1. It is important to note, however:
Red Hat Enterprise Linux 4 or 5.0 update installations are not tested or supported. A full system installation of Red Hat Enterprise Linux 5.1 is required
A mix of Red Hat Enterprise Linux 4 and 5 components is not supported. You will not be able to drop the MRG Realtime kernel and glibc into Red Hat Enterprise Linux 4 because of dependencies.
Red Hat Enterprise Linux 5.0 is not supported for use with MRG Realtime.
When doing the initial operating system installation, you should select the set of packages that meet the needs of your application environment. Nothing MRG Realtime specific is required on the initial install.
Once you have installed Red Hat Enterprise Linux 5.1 follow the instructions given at Section 2.2, “Installing MRG Realtime using Yum” to add the MRG Realtime specific packages from a separate yum repository.
MRG Realtime differs substantially from the standard Red Hat Enterprise Linux 5.1 kernel. The following list itemizes several differences:
Physical Address Extension (PAE) is configured in the x86 MRG Realtime kernel
Red Hat Enterprise Linux 5.1 for x86 (32 bit) includes the following kernel variants (using example version numbers which will vary)
kernel-2.6.18-8.el5 - this kernel does not have PAE enabled.
kernel-PAE-2.6.18-8.el5 - this kernel does have PAE enabled - allowing it to access more than 4GB of memory
In the MRG Realtime x86 kernel PAE is configured as we anticipate that most systems requiring RT capability will have at least 4GB of memory.
Note: the maximum memory supported on x86 systems is 16GB (which is the same limit as standard Red Hat Enterprise Linux 5.1). Larger memory configurations are supported on the x86-64 kernel.
Third-party kernel modules are incompatible with standard Red Hat Enterprise Linux 5.1
Kernel modules are inherently specific to the kernel they are built for. Since the MRG Realtime kernel is substantially different from the standard Red Hat Enterprise Linux 5.1 kernel, kernel modules are incompatible. In other words, you can't take third-party driver modules from Red Hat Enterprise Linux 5.1 and use them as-is on MRG Realtime.
The following are some example third-party drivers which ship for standard Red Hat Enterprise Linux 5.1 which do not currently have a MRG Realtime build:
EMC Powerpath
NVidia graphics
Advanced storage adapter configuration utilities from Qlogic
Emulex.
The user space syscall interface is compatible with standard Red Hat Enterprise Linux 5.1. These compatibility restrictions pertain only to kernel modules not supplied by Red Hat.