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LPC: Booting and systemd
Posted Sep 15, 2011 13:20 UTC (Thu) by dan_a (subscriber, #5325)
I quite enjoy doing kernel upgrades with GRUB. If you've never seen a system with a blank screen except for "LI" then you've not been using Linux very long!
Posted Sep 15, 2011 15:02 UTC (Thu) by epa (subscriber, #39769)
A simple command interpreter built into the kernel would also be a great help, e.g. when it can't find the root filesystem or /sbin/init.
Posted Sep 15, 2011 15:12 UTC (Thu) by rfunk (subscriber, #4054)
Posted Sep 16, 2011 14:38 UTC (Fri) by Cato (subscriber, #7643)
Posted Sep 19, 2011 9:33 UTC (Mon) by epa (subscriber, #39769)
Earlier Fedora releases gave about a hundred megs to /boot but then cannot be upgraded to the latest Fedora version, since the upgrade process needs to put a disk image in there too. (There is a way to download the disk image over the network but for me it always hangs.)
Posted Sep 20, 2011 9:56 UTC (Tue) by Cato (subscriber, #7643)
Posted Sep 20, 2011 16:06 UTC (Tue) by mathstuf (subscriber, #69389)
I actually did do a yum upgrade (from F10 to F11 IIRC) on the machine. The RPMs fit, but not with the upgrade going. I ended up having to SIGSTOP yum, delete cached RPMs that had finished installing for disk space, and the SIGCONT yum again. Not something I plan on doing again. Especially during class.
Posted Sep 15, 2011 18:06 UTC (Thu) by dlang (✭ supporter ✭, #313)
yes, it's easier to trigger lilo problems, but when grub doesn't just 'do the right thing', figuring out how to fix it seems to be much harder.
Posted Sep 16, 2011 17:19 UTC (Fri) by jmorris42 (subscriber, #2203)
Well what is old is now new again. GRUB2 requires running an installer after any change, such as installing a newly built kernel. Forget that step and kaboom! Well you get the old config with no mention of the newly installed kernel if you weren't so unwise as to get rid of the current running kernel before rebooting but we still went backward with GRUB2.
Posted Sep 16, 2011 17:34 UTC (Fri) by jrn (subscriber, #64214)
Forget that step and you have to type the name of the kernel by hand, you mean, right?
Posted Sep 22, 2011 22:29 UTC (Thu) by Wol (guest, #4433)
Many mobos do not do proper USB->PS2 emulation (some don't do it at all) so if all you have is a usb keyboard, you're stuffed. You can't tell grub which option you want so you get the choice of default, default or default. Tough luck if your upgrade broke but you made that the default in order to test it ...
For example, my mobo is broken some of the time - kernel upgrades are a pain because I never know whether my keyboard is going to work with grub or not :-(
Posted Sep 17, 2011 0:20 UTC (Sat) by giraffedata (subscriber, #1954)
Maybe we should just go back to LILO. Why boot an intermediate kernel with some added complexity if you can just boot the real one, instead.
Because you'd like to have a choice at boot time of kernels and kernel parameters. Hence the intermediate program, be it LILO, GRUB, or Linux.
If you really don't want that boot-time choice, then you should step back beyond LILO to the system that simply loads the first N blocks from the disk and branches to it. That can be your Linux boot image, with built-in parameters.
Even LILO is dependent on Linux filesystem design more than is desirable. It assumes a file is simply the content of a sequence of blocks, and that that sequence is static. A modern filesystem should not be bound to that.
Posted Sep 18, 2011 17:14 UTC (Sun) by raven667 (subscriber, #5198)
I'm just kind of talking out of my rear end here so maybe it's not like that at all but that's the sense that I get sometimes.
I wonder if grub EFI is an EFI loadable module or a more traditional x86 bootloader, something like that could have just been specified in the standard such that EFI could natively boot Win*, Linux, *BSD, etc. on common filesystems without any further installs or intermediaries. That would probably require compromise on the design which is always hard to get.
Posted Sep 18, 2011 18:26 UTC (Sun) by giraffedata (subscriber, #1954)
One could squeeze the GRUB and EFI layers into one, but look what you'd lose: Today, if I want to start determining kernel parameters in a new way, I can just update GRUB on my boot disk. If I mess it up so the system won't boot, that's OK - I can just tell EFI to boot from my backup boot disk (maybe a rescue CD) and fix it. But if all that parameter stuff was in EFI, I would have to flash a new EFI onto the motherboard, which isn't as easy. And if I screw it up, I might have a brick.
We can argue forever on how many layers are optimal, and what should go in each one (I'm hearing more and more opinions that GRUB2 has features that would better reside at the Linux kernel layer), but it's clear that having lots of bootstrap layers can be useful.
Posted Sep 18, 2011 20:06 UTC (Sun) by raven667 (subscriber, #5198)
Interestingly enough, elsewhere in LWN was a report of progress in making a linux kernel image that is directly bootable from EFI.
Posted Sep 18, 2011 18:40 UTC (Sun) by mjg59 (subscriber, #23239)
Posted Sep 18, 2011 20:11 UTC (Sun) by raven667 (subscriber, #5198)
Posted Sep 18, 2011 20:15 UTC (Sun) by mjg59 (subscriber, #23239)
In any case, EFI doesn't require that the firmware be able to read arbitrary filesystems. If you want to boot a kernel off LVM or btrfs or even ext2, you need a bootloader sitting in the EFI system partition.
Posted Sep 18, 2011 20:36 UTC (Sun) by raven667 (subscriber, #5198)
While it may be do-able to load modules for common filesystem types, as GRUB already does, so you can load kernels off them it seems more productive to be able to EFI boot the kernel directly and have the current and previous kernel images live on the EFI system partition. Basically make the EFI system partition replace the /boot directory.
Posted Sep 18, 2011 21:39 UTC (Sun) by mjg59 (subscriber, #23239)
Posted Sep 19, 2011 3:44 UTC (Mon) by raven667 (subscriber, #5198)
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