Is there a way to load the GRUB command line from within Linux?
This is primarily for educational purposes, so I don't have to keep turning my computer on and off again.
linux grub2
edited Feb 9 at 0:40
Rui F Ribeiro
40.4k1479137
asked Sep 29 '18 at 4:12
extremeaxe5extremeaxe5
23916
add a comment |
This is primarily for educational purposes, so I don't have to keep turning my computer on and off again.
linux grub2
edited Feb 9 at 0:40
Rui F Ribeiro
40.4k1479137
asked Sep 29 '18 at 4:12
extremeaxe5extremeaxe5
23916
Take a look at grub-emu, perhaps it's what you look for.
– ctac_
Sep 29 '18 at 10:24
add a comment |
This is primarily for educational purposes, so I don't have to keep turning my computer on and off again.
linux grub2
edited Feb 9 at 0:40
Rui F Ribeiro
40.4k1479137
asked Sep 29 '18 at 4:12
extremeaxe5extremeaxe5
23916
This is primarily for educational purposes, so I don't have to keep turning my computer on and off again.
linux grub2
linux grub2
edited Feb 9 at 0:40
Rui F Ribeiro
40.4k1479137
asked Sep 29 '18 at 4:12
extremeaxe5extremeaxe5
23916
edited Feb 9 at 0:40
Rui F Ribeiro
40.4k1479137
asked Sep 29 '18 at 4:12
extremeaxe5extremeaxe5
23916
edited Feb 9 at 0:40
Rui F Ribeiro
40.4k1479137
edited Feb 9 at 0:40
Rui F Ribeiro
40.4k1479137
edited Feb 9 at 0:40
Rui F Ribeiro
40.4k1479137
40.4k1479137
asked Sep 29 '18 at 4:12
extremeaxe5extremeaxe5
23916
asked Sep 29 '18 at 4:12
extremeaxe5extremeaxe5
23916
asked Sep 29 '18 at 4:12
extremeaxe5extremeaxe5
23916
23916
Take a look at grub-emu, perhaps it's what you look for.
– ctac_
Sep 29 '18 at 10:24
add a comment |
Take a look at grub-emu, perhaps it's what you look for.
– ctac_
Sep 29 '18 at 10:24
Take a look at grub-emu, perhaps it's what you look for.
– ctac_
Sep 29 '18 at 10:24
Take a look at grub-emu, perhaps it's what you look for.
– ctac_
Sep 29 '18 at 10:24
add a comment |
1 Answer
1
active
oldest
votes
I assume your question is about how to debug the boot process, i.e. testing whether a new grub configuration would work as expected, before rebooting for real:
It's possible with virtualization.
However, there are many corner cases if you just boot up your physical disk that's currently running your system again in a VM. You have to sync any outstanding writes to disk, flush caches, then start the VM with a strictly read-only view of the drive(s) (perhaps on a copy-on-write layer). You also have to disable network entirely - or it will download your emails and delete them from your server inside the VM where this data is then lost on shutdown.
And even then, the VM might just crash if it uses a filesystem that is already in use and being modified by the host. You could work around this problem using a proper snapshot but you usually can't just snapshot an entire drive and snapshotting a single LV won't help at all, as the VM will just see the same snapshot structure when it boots.
So it's best if the host stays idle and doesn't have filesystem activity while the VM is running, or simply stop the VM after the critical boot phase. Since the VM is read only you can just close it / kill it / no need for a proper shutdown inside the VM. So even if the VM crashes it doesn't really matter other than that it makes debugging difficult of course.
As long as you are aware of the ramifications, it comes down to a simple qemu, basically:
sync
echo 3 > /proc/sys/vm/drop_caches
qemu -net none -drive file=/dev/disk,readonly
# leave out readonly for a copy-on-write device:
qemu -net none -drive file=/dev/mapper/copy-on-write-disk
(qemu needs more options to run properly, check any qemu guide for more details - for example if you're using a distro like Gentoo that's strictly optimized for one type of CPU you also need -cpu host - but that's more or less the gist of it.)
answered Sep 29 '18 at 7:17
frostschutzfrostschutz
27.1k15584
add a comment |
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1 Answer
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1 Answer
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I assume your question is about how to debug the boot process, i.e. testing whether a new grub configuration would work as expected, before rebooting for real:
It's possible with virtualization.
However, there are many corner cases if you just boot up your physical disk that's currently running your system again in a VM. You have to sync any outstanding writes to disk, flush caches, then start the VM with a strictly read-only view of the drive(s) (perhaps on a copy-on-write layer). You also have to disable network entirely - or it will download your emails and delete them from your server inside the VM where this data is then lost on shutdown.
And even then, the VM might just crash if it uses a filesystem that is already in use and being modified by the host. You could work around this problem using a proper snapshot but you usually can't just snapshot an entire drive and snapshotting a single LV won't help at all, as the VM will just see the same snapshot structure when it boots.
So it's best if the host stays idle and doesn't have filesystem activity while the VM is running, or simply stop the VM after the critical boot phase. Since the VM is read only you can just close it / kill it / no need for a proper shutdown inside the VM. So even if the VM crashes it doesn't really matter other than that it makes debugging difficult of course.
As long as you are aware of the ramifications, it comes down to a simple qemu, basically:
sync
echo 3 > /proc/sys/vm/drop_caches
qemu -net none -drive file=/dev/disk,readonly
# leave out readonly for a copy-on-write device:
qemu -net none -drive file=/dev/mapper/copy-on-write-disk
(qemu needs more options to run properly, check any qemu guide for more details - for example if you're using a distro like Gentoo that's strictly optimized for one type of CPU you also need -cpu host - but that's more or less the gist of it.)
answered Sep 29 '18 at 7:17
frostschutzfrostschutz
27.1k15584
add a comment |
I assume your question is about how to debug the boot process, i.e. testing whether a new grub configuration would work as expected, before rebooting for real:
It's possible with virtualization.
However, there are many corner cases if you just boot up your physical disk that's currently running your system again in a VM. You have to sync any outstanding writes to disk, flush caches, then start the VM with a strictly read-only view of the drive(s) (perhaps on a copy-on-write layer). You also have to disable network entirely - or it will download your emails and delete them from your server inside the VM where this data is then lost on shutdown.
And even then, the VM might just crash if it uses a filesystem that is already in use and being modified by the host. You could work around this problem using a proper snapshot but you usually can't just snapshot an entire drive and snapshotting a single LV won't help at all, as the VM will just see the same snapshot structure when it boots.
So it's best if the host stays idle and doesn't have filesystem activity while the VM is running, or simply stop the VM after the critical boot phase. Since the VM is read only you can just close it / kill it / no need for a proper shutdown inside the VM. So even if the VM crashes it doesn't really matter other than that it makes debugging difficult of course.
As long as you are aware of the ramifications, it comes down to a simple qemu, basically:
sync
echo 3 > /proc/sys/vm/drop_caches
qemu -net none -drive file=/dev/disk,readonly
# leave out readonly for a copy-on-write device:
qemu -net none -drive file=/dev/mapper/copy-on-write-disk
(qemu needs more options to run properly, check any qemu guide for more details - for example if you're using a distro like Gentoo that's strictly optimized for one type of CPU you also need -cpu host - but that's more or less the gist of it.)
answered Sep 29 '18 at 7:17
frostschutzfrostschutz
27.1k15584
add a comment |
I assume your question is about how to debug the boot process, i.e. testing whether a new grub configuration would work as expected, before rebooting for real:
It's possible with virtualization.
However, there are many corner cases if you just boot up your physical disk that's currently running your system again in a VM. You have to sync any outstanding writes to disk, flush caches, then start the VM with a strictly read-only view of the drive(s) (perhaps on a copy-on-write layer). You also have to disable network entirely - or it will download your emails and delete them from your server inside the VM where this data is then lost on shutdown.
And even then, the VM might just crash if it uses a filesystem that is already in use and being modified by the host. You could work around this problem using a proper snapshot but you usually can't just snapshot an entire drive and snapshotting a single LV won't help at all, as the VM will just see the same snapshot structure when it boots.
So it's best if the host stays idle and doesn't have filesystem activity while the VM is running, or simply stop the VM after the critical boot phase. Since the VM is read only you can just close it / kill it / no need for a proper shutdown inside the VM. So even if the VM crashes it doesn't really matter other than that it makes debugging difficult of course.
As long as you are aware of the ramifications, it comes down to a simple qemu, basically:
sync
echo 3 > /proc/sys/vm/drop_caches
qemu -net none -drive file=/dev/disk,readonly
# leave out readonly for a copy-on-write device:
qemu -net none -drive file=/dev/mapper/copy-on-write-disk
(qemu needs more options to run properly, check any qemu guide for more details - for example if you're using a distro like Gentoo that's strictly optimized for one type of CPU you also need -cpu host - but that's more or less the gist of it.)
answered Sep 29 '18 at 7:17
frostschutzfrostschutz
27.1k15584
I assume your question is about how to debug the boot process, i.e. testing whether a new grub configuration would work as expected, before rebooting for real:
It's possible with virtualization.
However, there are many corner cases if you just boot up your physical disk that's currently running your system again in a VM. You have to sync any outstanding writes to disk, flush caches, then start the VM with a strictly read-only view of the drive(s) (perhaps on a copy-on-write layer). You also have to disable network entirely - or it will download your emails and delete them from your server inside the VM where this data is then lost on shutdown.
And even then, the VM might just crash if it uses a filesystem that is already in use and being modified by the host. You could work around this problem using a proper snapshot but you usually can't just snapshot an entire drive and snapshotting a single LV won't help at all, as the VM will just see the same snapshot structure when it boots.
So it's best if the host stays idle and doesn't have filesystem activity while the VM is running, or simply stop the VM after the critical boot phase. Since the VM is read only you can just close it / kill it / no need for a proper shutdown inside the VM. So even if the VM crashes it doesn't really matter other than that it makes debugging difficult of course.
As long as you are aware of the ramifications, it comes down to a simple qemu, basically:
sync
echo 3 > /proc/sys/vm/drop_caches
qemu -net none -drive file=/dev/disk,readonly
# leave out readonly for a copy-on-write device:
qemu -net none -drive file=/dev/mapper/copy-on-write-disk
(qemu needs more options to run properly, check any qemu guide for more details - for example if you're using a distro like Gentoo that's strictly optimized for one type of CPU you also need -cpu host - but that's more or less the gist of it.)
answered Sep 29 '18 at 7:17
frostschutzfrostschutz
27.1k15584
answered Sep 29 '18 at 7:17
frostschutzfrostschutz
27.1k15584
answered Sep 29 '18 at 7:17
frostschutzfrostschutz
27.1k15584
answered Sep 29 '18 at 7:17
frostschutzfrostschutz
27.1k15584
27.1k15584
add a comment |
add a comment |
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Take a look at grub-emu, perhaps it's what you look for.
– ctac_
Sep 29 '18 at 10:24