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lars_the_bear
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Joined: 05 Jun 2024
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 Posted: Sat Sep 14, 2024 3:05 pm Post subject: How does an 'emerge @world' update lead to updating grub.cfg |
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H folks
I'm trying to understand the sequence of events that leads to grub.cfg being updated, when I do a regular update using `emerge ... @world`. When there is a new kernel in the update, the new bits get installed in /boot, and I note that grub.cfg is automatically updated to reflect the changes. I have a customized grub.cfg on one of my machines, because it reads the kernel from one disk and the kernel's root filesystem from another.
Are the changes to grub.cfg made just by something running 'grub-mkconfig', or is there more to it than that? If' it's just `grub-mkconfig`, I can just write a script to update the auto-generated grub.cfg -- `grub-mkconfig` already has provision for that. If it's something more complicated, perhaps I need a different approach?
BR, Lars |
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sMueggli
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Joined: 03 Sep 2022
Posts: 489
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| Posted: Sat Sep 14, 2024 3:21 pm Post subject: |
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It is probably done by installkernel.
And customising /boot/grub/grub.cfg is a bad idea as the header of the file clearly shows:
| Code: | #
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
# |
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Hu
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Joined: 06 Mar 2007
Posts: 22618
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| Posted: Sat Sep 14, 2024 3:48 pm Post subject: |
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| emerge @world does not, on its own, touch boot at all. Some packages might touch that, and your emerge might pull in such a package. Other users may be using a kernel package that does not touch boot. Therefore, it would help if you told us exactly what "a new kernel in the update" means for you. For me, it means a new sys-kernel/gentoo-sources, which I then need to build and install outside Portage, so that package does not touch my boot. I could switch to one of the more automated mechanisms, but the benefit is not worth the time I would spend making it work like I want. |
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pietinger
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Joined: 17 Oct 2006
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Location: Bavaria
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lars_the_bear
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Joined: 05 Jun 2024
Posts: 517
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| Posted: Sat Sep 14, 2024 6:26 pm Post subject: |
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| pietinger wrote: |
Yes ... "installkernel" is able to do this ... and will do start grub-mkconfig IF you have enabled the use-flag "grub" for this package. |
Thank you. Yes I do have this use-flag, because the installation instructions say to add it. I didn't know what it did until today 
| Quote: |
And customising /boot/grub/grub.cfg is a bad idea as the header of the file clearly shows:
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Maybe so. I make my changes using a script in /etc/grub.d, which I believe is the documented way to do it -- if you're running 'grub-mkconfig'. That's why I needed confirmation that this utility was invoked. Not making the changes is not an option in my set-up.
BR, Lars. |
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pjp
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Joined: 16 Apr 2002
Posts: 20484
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| Posted: Sun Sep 15, 2024 4:51 am Post subject: |
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| sMueggli wrote: | And customising /boot/grub/grub.cfg is a bad idea as the header of the file clearly shows:
| Code: | #
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
# |
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That's only true if you use grub-mkconfig. I don't and have no trouble managing it as prior to grub2.
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sMueggli
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Joined: 03 Sep 2022
Posts: 489
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| Posted: Sun Sep 15, 2024 8:40 am Post subject: |
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| lars_the_bear wrote: | | Quote: |
And customising /boot/grub/grub.cfg is a bad idea as the header of the file clearly shows:
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Maybe so. I make my changes using a script in /etc/grub.d, which I believe is the documented way to do it -- if you're running 'grub-mkconfig'. That's why I needed confirmation that this utility was invoked. Not making the changes is not an option in my set-up.
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Yes, changing the Grub configuration via /etc/default/grub and scripts in /etc/grub.d is the recommended way. Running grub-mkconfig will produce the desired output, regardless how many times it is invoked and which tool or user is executing it. |
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GDH-gentoo
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Joined: 20 Jul 2019
Posts: 1686
Location: South America
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| Posted: Sun Sep 15, 2024 10:29 pm Post subject: |
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| pjp wrote: | | sMueggli wrote: | And customising /boot/grub/grub.cfg is a bad idea as the header of the file clearly shows:
| Code: | #
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
# |
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That's only true if you use grub-mkconfig. I don't and have no trouble managing it as prior to grub2. |
And I have no trouble managing it manually before and after GRUB 2 I only use grub-mkconfig (and don't overwrite grub.cfg with its output when I do) on occasion to compare with what I have. Or as a starting point on new installations that don't have any grub.cfg yet.
The syntax and commands are very well documented in the Texinfo manual (info grub).
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| NeddySeagoon wrote: | | I'm not a witch, I'm a retired electronics engineer |
| Ionen wrote: | | As a packager I just don't want things to get messier with weird build systems and multiple toolchains requirements though |
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pjp
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Joined: 16 Apr 2002
Posts: 20484
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| Posted: Mon Sep 16, 2024 3:56 am Post subject: |
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I was simply clarifying that grub-mkconfig isn't required.
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lars_the_bear
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Joined: 05 Jun 2024
Posts: 517
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| Posted: Mon Sep 16, 2024 7:18 am Post subject: |
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| pjp wrote: | | I was simply clarifying that grub-mkconfig isn't required. |
Sure. But I'm finding that it gets run every time 'emerge ... @world' delivers a new kernel. Now I know how to stop it doing that but, of course, I have to remember to update grub.cfg myself every time the kernel updates.
BR, Lars. |
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mi_unixbird
Tux's lil' helper
Joined: 24 Jul 2015
Posts: 130
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| Posted: Mon Sep 16, 2024 6:14 pm Post subject: |
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| sMueggli wrote: | It is probably done by installkernel.
And customising /boot/grub/grub.cfg is a bad idea as the header of the file clearly shows:
| Code: | #
# DO NOT EDIT THIS FILE
#
# It is automatically generated by grub-mkconfig using templates
# from /etc/grub.d and settings from /etc/default/grub
# |
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No, the file says that if it be generated by grub-mkconfig, and grub-itself says on the matter:
| Quote: | | grub-mkconfig does have some limitations. While adding extra custom menu entries to the end of the list can be done by editing /etc/grub.d/40_custom or creating /boot/grub/custom.cfg, changing the order of menu entries or changing their titles may require making complex changes to shell scripts stored in /etc/grub.d/. This may be improved in the future. In the meantime, those who feel that it would be easier to write grub.cfg directly are encouraged to do so |
It would be an absolute disaster if grub2-mkconfig were somehow required. As Grub itself says, customizing very simple things with it is arcane science and it basically guesses based on heuristics what the menu should look like and it generally becomes overcomplicated, unreadable soup. My grub.cofg is simply:
| Code: |
timeout=2
default=0
insmod all_video
set root=(hd1,gpt2)
menuentry 'desktop login' {
linux /boot/vmlinuz root=/dev/nvme0n1p2 init=/sbin/runit-init ro quiet net.ifnames=0 acpi_enforce_resources=lax autologin=user
}
menuentry 'agetty' {
linux /boot/vmlinuz root=/dev/nvme0n1p2 init=/sbin/runit-init ro quiet text net.ifnames=0 acpi_enforce_resources=lax
}
menuentry 'single' {
linux /boot/vmlinuz root=/dev/nvme0n1p2 init=/sbin/runit-init ro quiet text single
}
menuentry 'init=/bin/bash' {
linux /boot/vmlinuz root=/dev/nvme0n1p2 ro init=/bin/bash
}
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The bottom two entries are honestly useless. If I ever need to use them for recovery I might as well use sysrescueCD or something but havng them doesn't hurt.
There is a longstanding myth that Grub2 configuration is impossibly complicated and impossible to understand for mere mortal men due to the things generated by grub2-mkconfig. I think anyone who looks at this configuation can see what it does without a lot of schooling on the matter. It's clean, simple and understandable. I just looked at the output of grub2-mkconfig on my system. It finds some kind of initial ramdisk somewhere which I don't use. But something resembling one in my /boot apparently exists. I don't even know how it got there and it loads all sorts of modules and filesystems and by the looks of it will attempt to start with /sbin/init as my init while I use /sbin/runit-init. It generates a 500 line file opposed to this simple 20 line file.
| sMueggli wrote: | | lars_the_bear wrote: | | Quote: |
And customising /boot/grub/grub.cfg is a bad idea as the header of the file clearly shows:
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Maybe so. I make my changes using a script in /etc/grub.d, which I believe is the documented way to do it -- if you're running 'grub-mkconfig'. That's why I needed confirmation that this utility was invoked. Not making the changes is not an option in my set-up.
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Yes, changing the Grub configuration via /etc/default/grub and scripts in /etc/grub.d is the recommended way. Running grub-mkconfig will produce the desired output, regardless how many times it is invoked and which tool or user is executing it. |
Recomended by whom? As I quoted the GRUB documentation. It acknowledges the limitations of this approaches and encourages whoever finds it easier to edit it directly to do so.
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pjp
Administrator
Joined: 16 Apr 2002
Posts: 20484
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| Posted: Tue Sep 17, 2024 3:14 am Post subject: |
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| lars_the_bear wrote: | | pjp wrote: | | I was simply clarifying that grub-mkconfig isn't required. |
Sure. But I'm finding that it gets run every time 'emerge ... @world' delivers a new kernel. Now I know how to stop it doing that but, of course, I have to remember to update grub.cfg myself every time the kernel updates.
BR, Lars. |
So far I've only installed sys-kernel/gentoo-kernel-bin one time, so I don't really know how all that works. I typically build and update my own explicitly and not by using @world (I'm no expert). The "new" grub-mkconfig method was excruciatingly obtuse and I never took the time to learn how it works. A long time ago a helpful forum poster commented how the old way still worked in grub2 (I think it's very slightly different), so I've continued to use that because it isn't broke, and I don't know how to fix the new "and improved" way :).
I don't recall how I installed that gentoo-kernel-bin, but the grub.cfg file very much resembles how I do it manually, so I presume that's how I did it. :).
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