Sometimes I am required to restart my Ubuntu machine and don't want to go through the BIOS then Grub. I remember that in windows we just need to hold down the Shift Key while clicking restart and trying the same procedure in Ubuntu without any success.

  • This is a duplicate! See here: askubuntu.com/questions/152661/warm-reboot-directly-to-grub – Frantique Oct 3 '12 at 7:47
  • @Frantique No, I don't think my question is duplicate as the above link speaks about directly booting to Grub bypassing the BIOS and I am talking about bypassing all those thing BIOS and the GRUB too. I also want to restart from within my Ubuntu system might be with some modification and not making any changes to Firmware(Motherboard). – Namshum Oct 3 '12 at 8:04
  • 1
    Could you please edit your question to include why you would want to restart the way you describe as opposed to doing a proper restart? – user25656 Oct 3 '12 at 8:17
  • Ok, what about sudo kill -9 -1? – Frantique Oct 3 '12 at 8:42
  • @Frantique I used your code and it instantly makes the Screen dark just like expanded terminal (CUI) with a frozen cursor and had to restart my PC pressing the reset button. – Namshum Oct 4 '12 at 6:48

You can try out the kexec-tools (http://en.wikipedia.org/wiki/Kexec) by installing them using

sudo apt-get install kexec-tools

and allowing them to handling reboots on installation. Try out a reboot, if your machine comes up without troubles, you're good to go.

  • This actually does not make reboots faster for me ( it takes longer to shut down and then kernel takes 7 seconds to boot as compared to less than 2 when using normal reboot), is that expected? – sup May 3 '15 at 22:29
  • Absolutely not, for me it's just the same as a reboot minus the BIOS Time. I have only one idea, why that could be: A device has to be waited for (old hard disk, e.g. SCSI, ...) Anything special with the hardware? – Informatom May 5 '15 at 3:54
  • 1
    No, a standard laptop, Thinkpad W530 by Lenovo. First it flickers during shutdown (very weird graphical effects) and then it takes much longer to boot:-/. I am using an EFI install, if that might make a difference. – sup May 5 '15 at 8:29
  • @sup I also had devices, that made problems, one was an old laptop, that didn't lighten the display again after reboot. Another one failed reactivating a modem/sim card slot. Sorry, no I'm out of ideas. – Informatom May 6 '15 at 8:51
  • 1
    Ha, I messed with systemd a bit (mainly to disable unneeded services to make it boot faster) and now it is quick enough (about two seconds, so reboot takes altogether like 7 seconds). However, it still flickers: youtube.com/watch?v=2jDkEEjb0qA&feature=youtu.be- I disabled plymouth (removed quit-splash from grub config) an the flicker is gone. – sup May 6 '15 at 12:12

On standard x86 PCs address 0x472 controls whether or not one does a cold or warm reboot. By writing 0x1234 to this address, the BIOS should do a warm reboot, and if zero is written to this address a cold reboot will occur.

This can be controlled with the kernel parameter reboot=w (warm) or reboot=c (cold). So using sudo and your favourite editor, edit /etc/default/grub and change



GRUB_CMDLINE_LINUX_DEFAULT="quiet splash reboot=w"

and save. Then run:

sudo update-grub

and reboot. Hopefully, you should be doing warm reboots from now on. I've not tested this, but the code is there in the kernel to support this, see arch/x86/kernel/reboot.c in the kernel source and how reboot_type controls the reboot.

  • lan king I have edit grub and then update but when I click restart it still goes through all the procedure bios, grub etc. and also ubuntu now restart immediately without waiting to close for any open application. – Namshum Oct 7 '12 at 12:22

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.