-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 05/18/2014 01:46 PM, Vladimir '?-coder/phcoder' Serbinenko wrote: > On 18.05.2014 19:16, SevenBits wrote: >> On 05/18/2014 01:33 AM, Z C wrote: >>> If I boot into a linux kernel using a grub command like "linux >>> /vmlinuz; inirtd /initrd; boot", how do I shutdown linux >>> itself (but do not power off or reboot the computer hardware) >>> and return back to the grub directly? >> >> You can't. >> >> >>> What I meant is something equivalent to the "exit" command in >>> most shells: If you are within one shell and you enter another >>> shell, then if you want to quit the second shell and return >>> back to the first shell, just simply type exit. All env >>> variables and commands you previous typed in the first shell >>> are completely intact. >> >>> Suppose I am now in the grub shell, and then I boot into a >>> tiny linux kernel, say, a busybox shell, then what can I do to >>> exit the second shell (i.e. busybox shell) and return to the >>> first shell (i.e. grub shell)? Of course I can enter the grub >>> shell again by simply rebooting the hardware, but this is not >>> what I want. >> >> When Linux boots, the kernel takes over the management of the >> computer completely. The boot loader is not preserved in memory. >> Why would it be? The function of the boot loader really is to >> just boot up the computer and then get the heck out. >> >> There are many, many obstacles to implementing something like >> this. Not to mention the fact that in order to return to GRUB, >> you would need to set the processor to return from protected mode >> into real mode. All modern processors can do from real mode to >> protected mode (which you must do to enabled 32 bit processing). >> > Please update your sources. Last CPU that behaved like this is 286. > 386 and later can switch between modes in any direction.
Hi, yes, I actually realized this and posted an addendum to this message shortly afterwards. I don't know if you received it, but here is what I wrote: > Actually, a correction to what I just said. A processor can return > from protected mode to real mode. Read more here: > > https://en.wikipedia.org/wiki/Protected_mode#Entering_and_exiting_protected_mode > > I don't know if GRUB supports this (I would assume so) but > generally speaking it is still not possible to do what you want > because the Linux kernel as far as I know does not have the > functionality that would be required. If you want to try and do > this, go ahead and attempt it, but the roadblocks will be so large > that it probably is not worth trying, and just simply rebooting the > machine is the best way to get to GRUB. > > If you tell us what are _trying_ to do, i.e what you need this > functionality for, perhaps we can suggest an alternative way to > achieve what you need. So, yes, I realized after I posted my message that what I said was wrong. My apologies. > GRUB itself run in protected (but not paged mode) and switches to > real mode to call BIOS functions. "Returning" to GRUB would be > technically feasible but very cumbersome. Original requester didn't > even tell what his end goal is and it probably can be achieved in > much less cumbersome way. My thoughts exactly. >> So, no. It isn't possible. >> >> >> >> >>> _______________________________________________ Grub-devel >>> mailing list Grub-devel@gnu.org >>> https://lists.gnu.org/mailman/listinfo/grub-devel >> >> >> _______________________________________________ Grub-devel >> mailing list Grub-devel@gnu.org >> https://lists.gnu.org/mailman/listinfo/grub-devel . >> > > > > > _______________________________________________ Grub-devel mailing > list Grub-devel@gnu.org > https://lists.gnu.org/mailman/listinfo/grub-devel > -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.14 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQEcBAEBAgAGBQJTePN6AAoJEFbRvtGxmFPE7coH/12UTfimb2bONnDsJY3dFbTu Ti/xJ85n60fk3DFdCZ03ksqXfzGLjCeMHK8CzyhSCsUr7yFSAgB/9wEnxyc1XDDM 4msE6864xWHlzGSwzGkDyzdbbe0GiPIEGeVbgsnACsSF9JzsC3H08Y6bBF6DOF75 hGkgSJff8Su6oGTZPJpRV99MaKdThjgQkU6B7olOpGSbIzhf6/mrlCfTkJh14bdu PqsnVcdTSR8xkiZjn5aUGRkXapwl2IE+2jE+lmrFZRWDSRsCggykESa7gMUArCvg aTd66lj1gex6LmmujT9tsxwewYQnBYZC6JcXQB3KamISaJghPhB8eVvA5Ps3V2I= =G998 -----END PGP SIGNATURE----- _______________________________________________ Grub-devel mailing list Grub-devel@gnu.org https://lists.gnu.org/mailman/listinfo/grub-devel