ORA-00445: background process "W001" did not start after 120 seconds

Cause

* Recent linux kernels have a feature called Address Space Layout Randomization (ASLR).

* ASLR  is a feature that is activated by default on some of the newer linux distributions.

* It is designed to load shared memory objects in random addresses.

* In Oracle, multiple processes map a shared memory object at the same address across the processes.

* With ASLR turned on Oracle cannot guarantee the availability of this shared memory address.

This conflict in the address space means that a process trying to attach a shared memory object to a specific address may not be able to do so, resulting in a failure in shmat subroutine.

However, on subsequent retry (using a new process) the shared memory attachment may work. The result is a “random” set of failures in the alert log.

Solution

* It should be noted that this problem has only been positively diagnosed in Redhat 5 and Oracle 11.2.0.2.

* It is also likely, as per unpublished BUG:8527473,  that this issue will reproduce running on Generic Linux platforms  

   running any Oracle 11.2.0.x. or 12.1.0.x  on Redhat/OEL kernels which have ASLR. 

* This issue has been seen in both Single Instance and RAC environments.

You can verify whether ASLR is being used as follows:

 # /sbin/sysctl -a | grep randomize

kernel.randomize_va_space = 1

If the parameter is set to any value other than 0 then ASLR is in use. On Redhat 5 to permanently disable ASLR. Add/modify this parameter in /etc/sysctl.conf

-       kernel.randomize_va_space=0

-       kernel.exec-shield=0

You need to reboot for kernel.exec-shield parameter to take effect. Note that both kernel parameters are required for ASLR to be switched off.

There may be other reasons for a process failing to start, however, by switching ASLR off, you can quickly discount ASLR being the problem. More and more issues are being identified when ASLR is in operation.

References:

http://terryebase.com/?p=144