[F16] Why PAE kernel with 1 GB RAM?

[James Wilkinson]

Andreas M. Kirchwitz wrote:
> Freshly installed Fedora 16 for 32 bit (i686) from DVD on a Pentium 4
> with 1 GB RAM. Why does Fedora 16 installs a PAE kernel by default?
> Previous versions of Fedora (on that machine) did not install the
> PAE kernel but the regular one.

Does your Pentium 4 have NX/XD support? If the command
grep nx /proc/cpuinfo
returns anything, then you do.

NX is a security feature that requires PAE to work. It creates an extra
security barrier that malware has to get around.

> According to Red Hat, PAE comes with a performance hit from 0 to 10%.
Much closer to 0%: the 10% would be a worse case scenario.

If you’re going to throw security to the winds in the name of
performance, you might want to disable SELinux, too. I’d also recommend
keeping the machine away from the Internet and considering that a new
computer will be considerably faster than a Pentium 4.

> Unfortunately, the installation of the regular kernel & kernel-devel
> packages with "rpm -Uvh" from the DVD didn't update /boot/grub2/grub.cfg.
> Is there are clean way to make the non-PAE kernel the default kernel?

Well, you could try creating a new stanza in /boot/grub2/grub.cfg
yourself (yes, I know it says not to edit it), try rerunning
grub2-mkconfig to see if it puts the non-PAE kernel in there, or put a
suitable stanza in /etc/grub.d/40_custom (or 01_local, which you have to
create: see the README in /etc/grub.d), and then run grub2-mkconfig.

Note that you’ll have to redirect the output of grub2-mkconfig with
something like
grub2-mkconfig > /boot/grub2/grub.cfg

For a “suitable stanza”, look at grub2.cfg, find a “menuentry” command,
take all the text between there and the next } (including both the
menuentry and the }), and modify wherever it says /boot/whatever to
point to the equivalent file from the non-PAE kernel RPM.

Hope this helps,

James.

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