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I have had ubuntu running fine from usb external hd. When i bought a new laptop (toshiba L775D-S7222) and tried to boot I found that not always but sometimes there was a problem that shutdown did not poweroff rather restarted. Also when this happens my laptop keyboard and mouse dont work at all and I need to use external. When this happens I sometimes fing in the bios that internal mouse is disabled even though I know clearly that I left it enabled.

How can I go about debugging this?

some lines from dmesg:

[    2.770728] ehci_hcd 0000:00:16.2: QUIRK: Enable exception for AMD Hudson ASPM
[    2.770741] ehci_hcd 0000:00:16.2: applying AMD SB700/SB800/Hudson-2/3 EHCI dummy qh workaround
[    3.011495] powernow-k8: Found 1 AMD A6-3400M APU with Radeon(tm) HD Graphics (4 cpu cores) (version 2.20.00)


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did you try typing into the command line: 'sudo shutdown -h now`? – Thomas Ward Jul 29 '11 at 17:38
Same as me . If i push power button and choose poweroff it sometimes restart instead – Elias Alves Jul 11 '15 at 20:54

Not sure why it would restart, but halting is not the same as powering off. However, upstart actually confused things quite a bit by powering off when one called halt. Note that this bug was fixed in Ubuntu 11.10:

However, I'd suspect that if halt issued an ACPI power off command, and instead ended up rebooting the machine, that sounds like maybe a kernel problem or BIOS incompatibility.

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