# PAE Broken?



## criley (Jul 3, 2009)

Hi all I have 4 brand new servers for a upcoming project. They are all Dell 2950's with dual core dual processors. The issue I am running into is that they keep freaking out with issues on memory with Cannot fork: Cannot allocate memory errors when I try to compile them with a PAE kernel. If I run AMD64 they seem to play nicely however I am curious as to why PAE is freaking out. I am running some Dell 2850's with 16 Gig of Ram and PAE mode with no problems so I started playing with the dual core setting and noticed that if I change the dual core setting to single core then I can get the boxes a bit more stable but eventually they too will freak out. 

Suggestions?

Thanks in advance.


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## aragon (Jul 3, 2009)

More details would be helpful, but keep in mind that although PAE gives the operating system access to more than 4 GB of RAM in 32 bit mode, single processes are still limited to not more than 4 GB of RAM usage each.  This limitation might be what you're hitting.

Unless you have a specific reason, you really should be running AMD64.  PAE is an ugly hack with overheads that you pay in CPU time, and restrictions (like the above one) that keep you from really enjoying a modern system.


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## SeanC (Jul 4, 2009)

aragon said:
			
		

> PAE is an ugly hack with overheads that you pay in CPU time, and restrictions (like the above one) that keep you from really enjoying a modern system.



PAE is theoretically nice, but what it can do to your 32 bit system is ugly. Avoid at all costs.


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## maheshkasbe (Mar 3, 2010)

How to compile PAE kernel; please follows the following steps as root login

```
cd /usr/src/sys/i386/conf 
config PAE 
cd ../compile/PAE 
make cleandepend && make depend 
make  
make install 
reboot
```


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## DutchDaemon (Mar 3, 2010)

This is the old-fashioned way of building a kernel. See /usr/src/Makefile for the modern way of doing this ([cmd=]make buildkernel KERNCONF=PAE[/cmd], etc.).

And like other said: avoid PAE if you possibly can. Use a 64-bit OS.


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