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I know that 32-bit 10.04 enables PAE on installation when it detects 3+ GB RAM, but I'd like to know a way to manually check (i.e. in the terminal) that PAE is, in fact, enabled.

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up vote 4 down vote accepted

On current versions of Ubuntu on the 386 architecture, PAE is enabled on -generic-pae kernels but not on -generic or -virtual kernels, so you can check if the output uname -r ends with -pae. This isn't very robust though, since it depends on intimate knowledge of what Ubuntu uses for kernel options.

Some distributions provide the kernel configuration in /proc/config, so you can test with </proc/config fgrep -x CONFIG_X86_PAE=y. Ubuntu doesn't, but it does keep the kernel configuration in a well-known place, so you can test with </boot/config-$(uname -r) fgrep -x CONFIG_X86_PAE=y.

Note that grep -w pae /proc/cpuinfo tells you whether your processor supports PAE. The flag will be present whether the kernel supports PAE or not.

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Run cat /proc/cpuinfo | grep -i PAE from the Commandline. If it returns PAE then the Kernel is PAE enabled. - @Gilles says this returns whether the CPU supports PAE, not the Kernel.

Another way to check is run uname -r - it should contain reference to PAE if the kernel is PAE enabled

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Wrong, /proc/cpuinfo contains pae if the processor supports PAE, whether the kernel supports it or not. – Gilles Sep 20 '10 at 21:05
    
@Gilles Thanks for clarifying that. – Sathya Sep 20 '10 at 22:45

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