SAP Kernel upgrade

First question ----Why we do kernel upgrade??

My way of answer ---There are many reasons to upgrade kernel.In a basic way we need a new device driver for our old or new hardware.overall concept is we are reducing the bugs by using this new kernel.

Now lets jump in SAP.SAP system consists of kernel & applications.Kernel is the Central program for the SAP applications.We can always upgrade the kernel to higher release while leaving the applications in the original release.that is the reason Kernel is said to be "downward compatible" but it is limited to the same SAP release sequence.after kernel upgrade we gain using updated program patches & many other improvements which  I don't see from administrator side.

I always check the relevant SAP notes before i upgrade the kernel to make sure I am doing in a safe & quicker way.

Now lets start with my steps in  unix environment.

Firstly get the Kernel patchlevel info .steps to do that 

In sap level---SM51--> click on release notes.

                    ---System -->status-->click on the arrow mark with shows other kernel info 

In unix level --- disp+work -v | more

As per the Kernel info (For example SAP R3 ENTERPRISE)

go to service.sap.com/patches

Support Packages and Patches à SAP Application Componentsà SAP R/3 ENTERPRISEà SAP R/3 ENTERPRISE 47X110à Entry by Componentà SAP R/3 Enterprise Server

Download both sapexe & sapexedb files as per your OS & database for the latest patch level.

Please move these files to the unix box to one path ex: /user/newkernel

Now uncar the files using the command

SAPCAR -xvf  SAPEXEDB_247-10002837.SAR

SAPCAR -xvf SAPEXE_247-10002836.SAR

Now the main steps

1.Create a system message using sm02 transaction.(System will be down for kernel upgrade & will be back after 30 mins)

2.Log in as sidadm .Put the sap down

stopsap R3

stop saposcol

saposcol -k

3.Backup the old kernel 

cd /sapmnt/SID/exe

cp -pr *  /user/oldkernel

Check if backup is done properly 

du -sk /sapmnt/SID/exe -->930148

du -sk /usr/oldkernel -->930148

4.copy the new kernel directory 

cd /usr/newkernel

cp -pr * /sapmnt/SID/exe

Now login as root

./saproot.sh SID

(Reason-->Script will change the owner and the permission of related kernel file.ex:disp+work.exe owner will be sidadm brtools.exe will have oraadm)

Now again check if the new kernel is replaced by oldkernel

disp+work -v | more

5.start saposcol & sap .

Login as sidadm

saposcol -l

startsap R3

& Remove the system message which was posted before.

After the kernel upgrade bringing back the system is always not easy.You could be facing many issues.First place i would ask you to start troubleshooting by checking the worklogs.