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I'm using Ubuntu 14.04.2 LTS with kernel 3.16.0-38-generic #52~14.04.1-Ubuntu SMP Fri May 8 09:43:57 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux.

Computer model: iMac Late 2009 ( https://support.apple.com/kb/SP696?locale=en_US )

My computer is EFI based (not BIOS). And I don't see "noapic, nolapic" set in the grub config file.

I have an Intel(R) Core(TM)2 Duo CPU, but some times when I boot my system only 1 CPU core is detected.

Here's dmesg output when only core is detected:

[    0.000000] smpboot: Allowing 2 CPUs, 0 hotplug CPUs
[    0.073437] smpboot: CPU0: Intel(R) Core(TM)2 Duo CPU     E7600  @ 3.06GHz (fam: 06, model: 17, stepping: 0a)
[    5.088430] smpboot: CPU1: Not responding
[    5.088440] smpboot: do_boot_cpu failed(1) to wakeup CPU#1
[    5.088448] smpboot: Total of 1 processors activated (6102.83 BogoMIPS)
[    0.076000] Kernel panic - not syncing: smp_callin: CPU1 started up but did not get a callout!
[    0.076000] ---[ end Kernel panic - not syncing: smp_callin: CPU1 started up but did not get a callout!

Here's dmesg output when all of the cores are detected:

[    0.000000] smpboot: Allowing 2 CPUs, 0 hotplug CPUs
[    0.073319] smpboot: CPU0: Intel(R) Core(TM)2 Duo CPU     E7600  @ 3.06GHz (fam: 06, model: 17, stepping: 0a)
[    0.086922] smpboot: Total of 2 processors activated (12206.00 BogoMIPS)

USB devices:

$ lsusb 
Bus 002 Device 004: ID 05ac:8403 Apple, Inc. Internal Memory Card Reader
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 003: ID 045e:078c Microsoft Corp. 
Bus 004 Device 004: ID 05ac:8215 Apple, Inc. Built-in Bluetooth 2.0+EDR HCI
Bus 004 Device 002: ID 0a5c:4500 Broadcom Corp. BCM2046B1 USB 2.0 Hub (part of BCM2046 Bluetooth)
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 003: ID 05ac:8502 Apple, Inc. Built-in iSight
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 003 Device 003: ID 05ac:8242 Apple, Inc. Built-in IR Receiver
Bus 003 Device 002: ID 045e:0040 Microsoft Corp. Wheel Mouse Optical
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub

I only have a Microsoft old keyboard and mouse plugged (2 of 4 usb ports used).

What can I do to sort this out?

Thanks.

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  • do you have any external devices connected? somtimes this may cause issues: bbs.archlinux.org/viewtopic.php?id=159268
    – mchid
    May 25, 2015 at 17:28
  • What is the output of nproc in that system? If 2 then it is all fine, I guess.
    – n0noob
    May 25, 2015 at 17:47
  • I have old Microsoft keyboard and mouse connected via USB (I will check later if the problem persists with them unplugged at boot time). Now, the output of nproc is 2, but when I boot my system again it can be 1.
    – SKp
    May 25, 2015 at 18:07
  • A very interesting phenomenon, Keyboards shutting down CPU cores! Does any of your USB devices have a internal hub? Or do you use a hub? May 25, 2015 at 18:24
  • No, there are no hubs.
    – SKp
    May 25, 2015 at 18:29

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