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Old 09-25-2012, 03:59 AM   #1
kedarp
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PAE kernel headache


New distros have the PAE kernel. I have Ubuntu 12.04 but I cannot install it on my computer.
I have Core2Duo 7500 processor which is far more powerful than
the requirement. But I have to use the old distros becase it does not
support PAE. I don't expect any solution but I think that PAE kernels
should also support non-PAE processors like Windows.
non-PAE processors are not that old.
 
Old 09-25-2012, 04:29 AM   #2
414N
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Doesn't your processor support 64 bit instruction set (x86_64 or AMD64 or Intel64)?
If it doesn't, you can always recompile a kernel with no PAE support on the newer distro...
 
Old 09-25-2012, 04:34 AM   #3
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I understand your frustration. As a matter of fact, a lot of distributions are now shipping kernels with PAE.

This is an unavoidable consequence of selecting "64 GB" among the High Memory Support options.

So the only way would be to re-configure your kernel with the "4 GB" choice instead.
 
Old 09-25-2012, 06:22 AM   #4
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I would be very surprised if a Core 2 Duo CPU wouldn't support PAE. If you can start one of the older distros, what is the output of
Code:
cat /proc/cpuinfo
 
Old 09-25-2012, 07:00 AM   #5
Didier Spaier
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I think TobiSGD is right. Here uname -p says:

Intel(R) Core(TM)2 Duo CPU T7500 @ 2.20GHz

and pae is listed among the flags in cat /cpu/info's output.
 
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Old 09-25-2012, 07:32 AM   #6
TobiSGD
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The Core 2 Duo 7500 and the Core 2 Duo T7500 may possibly not have the same core, since one is the desktop and one the mobile version.
Nonetheless have I never seen a Core 2 Duo version without PAE.
 
Old 09-25-2012, 08:10 AM   #7
kedarp
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Code:
processor	: 0
vendor_id	: GenuineIntel
cpu family	: 6
model		: 23
model name	: Intel(R) Core(TM)2 Duo CPU     E7500  @ 2.93GHz
stepping	: 10
cpu MHz		: 1603.000
cache size	: 3072 KB
physical id	: 0
siblings	: 2
core id		: 0
cpu cores	: 2
apicid		: 0
initial apicid	: 0
fdiv_bug	: no
hlt_bug		: no
f00f_bug	: no
coma_bug	: no
fpu		: yes
fpu_exception	: yes
cpuid level	: 13
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx lm constant_tsc arch_perfmon pebs bts aperfmperf pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm sse4_1 xsave lahf_lm tpr_shadow vnmi flexpriority
bogomips	: 5866.73
clflush size	: 64
cache_alignment	: 64
address sizes	: 36 bits physical, 48 bits virtual
power management:

processor	: 1
vendor_id	: GenuineIntel
cpu family	: 6
model		: 23
model name	: Intel(R) Core(TM)2 Duo CPU     E7500  @ 2.93GHz
stepping	: 10
cpu MHz		: 1603.000
cache size	: 3072 KB
physical id	: 0
siblings	: 2
core id		: 1
cpu cores	: 2
apicid		: 1
initial apicid	: 1
fdiv_bug	: no
hlt_bug		: no
f00f_bug	: no
coma_bug	: no
fpu		: yes
fpu_exception	: yes
cpuid level	: 13
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx lm constant_tsc arch_perfmon pebs bts aperfmperf pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm sse4_1 xsave lahf_lm tpr_shadow vnmi flexpriority
bogomips	: 5866.56
clflush size	: 64
cache_alignment	: 64
address sizes	: 36 bits physical, 48 bits virtual
power management:
Here is /proc/cpuinfo. Yes pae is listed in flags.
Well I tried it in VirtualBox. I will try it as Live Distro and reply. Thanks.
 
Old 09-25-2012, 08:13 AM   #8
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In Virtualbox you have to explicitly enable PAE support in the settings for the VM.
 
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Old 09-25-2012, 08:25 AM   #9
zhjim
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What actually is the error you get when booting the kernel?
As I read on wikipedia: Most distributions come with PAE cause it's needed for the NX-Bit. Might that be the cause?
Does the mobo need that feature too? Does it has to be enabled in BIOS?
 
Old 09-25-2012, 10:26 AM   #10
Didier Spaier
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TobiSGD has the point here. I have even been hurt by that myself sometimes. We have to remember the the VirtualBox' CPUs are virtual, not real ones.
 
Old 09-25-2012, 10:35 AM   #11
414N
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Well, the fact that the OP was running on a virtual machine would have been the first thing to say...
 
Old 09-25-2012, 11:42 AM   #12
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Quote:
Originally Posted by 414N View Post
Well, the fact that the OP was running on a virtual machine would have been the first thing to say...
Maybe the first thing for experts to ask next time.

I don't expect the person asking the original question would guess that running on a VM is relevant to PAE not working (or if he did guess, would not have needed to ask).

This is not the first time at LQ that someone asked about PAE not working and gave a CPU model on which PAE should work and only later revealed that it was all tested under a VM.

I'm not faulting the experts who didn't make that guess earlier in this thread, just making a suggestion for next time, because I expect there will be a next time.

Last edited by johnsfine; 09-25-2012 at 11:44 AM.
 
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Old 09-25-2012, 03:47 PM   #13
sundialsvcs
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Virtualization is always somewhat of a deceiver. It tries so hard to give the illusion that "this is a real machine!!" ... that sometimes you forget that it is not. But the Linux operating-system kernel is one of those "edge cases" that can surprise you ... simply because it is so configurable to the needs of, ummmm, real hardware. Every virtualization scheme has to "overlook something," in order to "come acceptably close." But Linux kernels can nevertheless catch them out.
 
Old 09-26-2012, 01:10 AM   #14
kedarp
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I was able to run 12.04 in VM as well as live CD. Thanks to all especially TobiSGD and Didier for pointing it out that Core2Duo has PAE feature.
Otherwise I would never have installed PAE kernel.
And also I had not asked any question but got a solution.
 
  


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