Linode discontinuing Xen, migrating to KVM

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Linode discontinuing Xen, migrating to KVM

tanstaafl-2
Ok, so just got the notice that Linode is discontinuing their support
for Xen, and forcing everyone to migrate their VMs to KVM.

Of course this comes at the worst possible time for me, when I'm out of
the country, and won't be back before the deadline (the 9th).

I have a week, so am trying to do everything I can to ensure they come
up successfully. I have two, one production, and a second one we were
going to use as a dev/test server, but in reality, we don't use it,
although I want to keep it running too (will perform the migration on it
first).

I'm especially worried, because these VMs are running an ancient web
application that requires older versions of Apache, PHP and Postgresql,
so cannot be and haven't been updated in a very long time (I kept them
up to date as long as I could by pinning the old apps and testing
updates on the dev/test server until it just got to be too much work)...

They are both (thankfully) running a current Linode kernel, so I HOPE
this migration won't kill either of them.

One thing I do seem to recall is there was somewhere that I had to
define Xen as the virtualization environment being used, but I can't
remember where I did that. Was that in the kernel config? If so, their
tool should (hopefully) handle that change.

Anyway, was hoping some kind souls here might give me a few things to
check and possibly do proactively to ensure a smooth transition.

Emerge --info for each one attached

Thanks!

emerg--i


emerge-info-prod.txt (6K) Download Attachment
emerge-info-dev.txt (6K) Download Attachment
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Re: Linode discontinuing Xen, migrating to KVM

stroller-6

> On 2 Oct 2017, at 18:30, Tanstaafl <[hidden email]> wrote:
>
> One thing I do seem to recall is there was somewhere that I had to
> define Xen as the virtualization environment being used, but I can't
> remember where I did that. Was that in the kernel config? If so, their
> tool should (hopefully) handle that change.

See last lines:

~ $ grep -B 25 -ie xen -ie kvm /etc/rc.conf
# This is mainly used for saying which services do NOT provide net.
#rc_net_tap0_provide="!net"

# This is the subsystem type.
# It is used to match against keywords set by the keyword call in the
# depend function of service scripts.
#
# It should be set to the value representing the environment this file is
# PRESENTLY in, not the virtualization the environment is capable of.
# If it is commented out, automatic detection will be used.
#
# The list below shows all possible settings as well as the host
# operating systems where they can be used and autodetected.
#
# ""               - nothing special
# "docker"         - Docker container manager (Linux)
# "jail"           - Jail (DragonflyBSD or FreeBSD)
# "lxc"            - Linux Containers
# "openvz"         - Linux OpenVZ
# "prefix"         - Prefix
# "rkt"            - CoreOS container management system (Linux)
# "subhurd"        - Hurd subhurds (to be checked)
# "systemd-nspawn" - Container created by systemd-nspawn (Linux)
# "uml"            - Usermode Linux
# "vserver"        - Linux vserver
# "xen0"           - Xen0 Domain (Linux and NetBSD)
# "xenU"           - XenU Domain (Linux and NetBSD)
~ $

This on a Linode host, BTW. They haven't told me I need to do anything, so I hope I'm ok.

HTH,

Stroller.


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Re: Linode discontinuing Xen, migrating to KVM

tanstaafl-2
On 10/2/2017, 2:39:51 PM, Stroller <[hidden email]> wrote:

>
>> On 2 Oct 2017, at 18:30, Tanstaafl <[hidden email]> wrote:
>>
>> One thing I do seem to recall is there was somewhere that I had to
>> define Xen as the virtualization environment being used, but I can't
>> remember where I did that. Was that in the kernel config? If so, their
>> tool should (hopefully) handle that change.
>
> See last lines:
>
> ~ $ grep -B 25 -ie xen -ie kvm /etc/rc.conf
<snip>
> # "xen0"           - Xen0 Domain (Linux and NetBSD)
> # "xenU"           - XenU Domain (Linux and NetBSD)
> ~ $
>
> This on a Linode host, BTW. They haven't told me I need to do anything, so I hope I'm ok.
>
> HTH,

Thanks! Yes, at least now I know where that was specified... and since
there is nothing there for kvm, I guess you just leave it commented, BUT...

yours doesn't appear to be set?? Mine is set to "xenU".

So... maybe I've never even needed this? Or maybe I did way back when I
first installed this (probably 7 or 8 years ago), and it isn't needed
any longer? Would the need for it be based on the kernel version? OR the
underlying Xen Host version? Or something else?

More importantly - I guess I should comment it out right before the
migration? Or is this something I can do after? IF I don't, how would I
handle it?

Wish I had more time to learn about how all of this worked...

Anyway, thanks again for at least filling in one blank...

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Re: Linode discontinuing Xen, migrating to KVM

tanstaafl-2
On 10/2/2017, 4:03:37 PM, Tanstaafl <[hidden email]> wrote:

> On 10/2/2017, 2:39:51 PM, Stroller <[hidden email]> wrote:
>>
>>> On 2 Oct 2017, at 18:30, Tanstaafl <[hidden email]> wrote:
>>>
>>> One thing I do seem to recall is there was somewhere that I had to
>>> define Xen as the virtualization environment being used, but I can't
>>> remember where I did that. Was that in the kernel config? If so, their
>>> tool should (hopefully) handle that change.
>>
>> See last lines:
>>
>> ~ $ grep -B 25 -ie xen -ie kvm /etc/rc.conf
> <snip>
>> # "xen0"           - Xen0 Domain (Linux and NetBSD)
>> # "xenU"           - XenU Domain (Linux and NetBSD)
>> ~ $
>>
>> This on a Linode host, BTW. They haven't told me I need to do anything, so I hope I'm ok.
>>
>> HTH,
>
> Thanks! Yes, at least now I know where that was specified... and since
> there is nothing there for kvm, I guess you just leave it commented, BUT...
>
> yours doesn't appear to be set?? Mine is set to "xenU".

Also, yours shows 12 different choices, mine only shows 8:

##############################################################################
# LINUX SPECIFIC OPTIONS

# This is the subsystem type. Valid options on Linux:
# ""        - nothing special
# "lxc"     - Linux Containers
# "openvz"  - Linux OpenVZ
# "prefix"  - Prefix
# "uml"     - Usermode Linux
# "vserver" - Linux vserver
# "xen0"    - Xen0 Domain
# "xenU"    - XenU Domain
# If this is commented out, automatic detection will be used.
#

Wonder why that is?

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Re: Linode discontinuing Xen, migrating to KVM

R0b0t1
In reply to this post by tanstaafl-2
Hello friends!

On Mon, Oct 2, 2017 at 3:03 PM, Tanstaafl <[hidden email]> wrote:

> On 10/2/2017, 2:39:51 PM, Stroller <[hidden email]> wrote:
>>
>>> On 2 Oct 2017, at 18:30, Tanstaafl <[hidden email]> wrote:
>>>
>>> One thing I do seem to recall is there was somewhere that I had to
>>> define Xen as the virtualization environment being used, but I can't
>>> remember where I did that. Was that in the kernel config? If so, their
>>> tool should (hopefully) handle that change.
>>
>> See last lines:
>>
>> ~ $ grep -B 25 -ie xen -ie kvm /etc/rc.conf
> <snip>
>> # "xen0"           - Xen0 Domain (Linux and NetBSD)
>> # "xenU"           - XenU Domain (Linux and NetBSD)
>> ~ $
>>
>> This on a Linode host, BTW. They haven't told me I need to do anything, so I hope I'm ok.
>>
>> HTH,
>
> Thanks! Yes, at least now I know where that was specified... and since
> there is nothing there for kvm, I guess you just leave it commented, BUT...
>
> yours doesn't appear to be set?? Mine is set to "xenU".
>

Due to the nature of how both Xen and QEMU/KVM work, there is no need
to set any kernel configuration that tells the kernel it is running on
virtual hardware. However, if you do so, you will see performance
gains.

Some of these performance gains are visible outside of the virtualized
system so hosting providers would be within their rights to require
specific configuration, but I expect they would have made it obvious.

Refer to https://wiki.gentoo.org/wiki/QEMU/Linux_guest, but these
settings require support from Linode.

> So... maybe I've never even needed this? Or maybe I did way back when I
> first installed this (probably 7 or 8 years ago), and it isn't needed
> any longer? Would the need for it be based on the kernel version? OR the
> underlying Xen Host version? Or something else?
>
> More importantly - I guess I should comment it out right before the
> migration? Or is this something I can do after? IF I don't, how would I
> handle it?
>

As long as your kernel has the appropriate drivers (i.e. you didn't
include only the virtualized Xen drivers and left most of the default
options intact) it should boot under QEMU/KVM or even on a bare metal
system.

Cheers,
     R0b0t1

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Re: Linode discontinuing Xen, migrating to KVM

victor romanchuk
In reply to this post by tanstaafl-2
hi

On 10/02/2017 08:30 PM, Tanstaafl wrote:
> One thing I do seem to recall is there was somewhere that I had to
> define Xen as the virtualization environment being used, but I can't
> remember where I did that. Was that in the kernel config? If so, their
> tool should (hopefully) handle that change.
>
> Anyway, was hoping some kind souls here might give me a few things to
> check and possibly do proactively to ensure a smooth transition.
>

there are two files to change/check before migration

  * /etc/inittab :: console terminal (XEN PV domUs do use hvc console and KVM VM employ normal linux
    console)

    -c1:12345:/respawn:/sbin/agetty 38400 hvc0 linux
    +c1:12345:respawn:/sbin/agetty 38400 ttyS0 linux

  *  /etc/fstab :: XEN PV do use xvdN volumes and KVM VM volume naming is canonical

    -/dev/xvdb        none        swap        sw        0 0
    +/dev/sdb        none        swap        sw        0 0


the migration itself is automated; linode did it for me flawlessly: few minutes of downtime needed
to convert images and to move them to different hardware (in my case)

hth


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Re: Linode discontinuing Xen, migrating to KVM

tanstaafl-2
On 10/3/2017, 1:27:45 AM, victor romanchuk <[hidden email]> wrote:

> there are two files to change/check before migration
>
>   * /etc/inittab :: console terminal (XEN PV domUs do use hvc console and KVM VM employ normal linux
>     console)
>
>     -c1:12345:/respawn:/sbin/agetty 38400 hvc0 linux
>     +c1:12345:respawn:/sbin/agetty 38400 ttyS0 linux
>
>   *  /etc/fstab :: XEN PV do use xvdN volumes and KVM VM volume naming is canonical
>
>     -/dev/xvdb        none        swap        sw        0 0
>     +/dev/sdb        none        swap        sw        0 0
>
>
> the migration itself is automated; linode did it for me flawlessly: few minutes of downtime needed
> to convert images and to move them to different hardware (in my case)

Thanks - but I thought these were changed as part of the automated
process (from what I've read).

Did you change yours manually?

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Re: Linode discontinuing Xen, migrating to KVM

tanstaafl-2
In reply to this post by R0b0t1
On 10/2/2017, 11:52:21 PM, R0b0t1 <[hidden email]> wrote:
> As long as your kernel has the appropriate drivers (i.e. you didn't
> include only the virtualized Xen drivers and left most of the default
> options intact) it should boot under QEMU/KVM or even on a bare metal
> system.

Hmmm, something else I just remembered when I noticed my production
server is running a 32 bit kernel...

A long time ago, maybe 6 or 7 years, something weird happened when
Linode had some kind of problem (maybe it was another one of their
maintenance processes, I don't recall), I had a heck of a time getting
it back up, I finally had to do a full rebuild, and distinctly remember
changing to a 32 bit kernel during the process, but never changed back.

Do I need to do a full system rebuild to change back to the 64 bit kernel?

Also, I haven't played with Linodes 'System Profiles' at all - I was
thinking I'd just create a new profile, add my Gentoo System Image and a
swap image to it, but assign the 64 bit kernel, then if it doesn't work,
switch back. Should I be able to do that without causing any problems to
the current/working profile?

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Re: Linode discontinuing Xen, migrating to KVM

victor romanchuk
In reply to this post by tanstaafl-2
On 10/03/2017 02:28 PM, Tanstaafl wrote:

> On 10/3/2017, 1:27:45 AM, victor romanchuk <[hidden email]> wrote:
>> there are two files to change/check before migration
>>
>>   * /etc/inittab :: console terminal (XEN PV domUs do use hvc console and KVM VM employ normal linux
>>     console)
>>
>>     -c1:12345:/respawn:/sbin/agetty 38400 hvc0 linux
>>     +c1:12345:respawn:/sbin/agetty 38400 ttyS0 linux
>>
>>   *  /etc/fstab :: XEN PV do use xvdN volumes and KVM VM volume naming is canonical
>>
>>     -/dev/xvdb        none        swap        sw        0 0
>>     +/dev/sdb        none        swap        sw        0 0
>>
>> the migration itself is automated; linode did it for me flawlessly: few minutes of downtime needed
>> to convert images and to move them to different hardware (in my case)
> Thanks - but I thought these were changed as part of the automated
> process (from what I've read).
>
> Did you change yours manually?
>

I forgot it :)

most likely it was performed by linode automation at least what I'm seeing now confirms that (both
files were modified together):

$ stat /etc/inittab /etc/fstab
  File: '/etc/inittab'
  Size: 1937          Blocks: 4          IO Block: 1024   regular file
Device: 800h/2048d    Inode: 102725      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2017-09-11 23:46:24.000000000 +0300
Modify: 2017-09-11 23:46:24.000000000 +0300
Change: 2017-09-11 23:46:24.000000000 +0300
 Birth: -
  File: '/etc/fstab'
  Size: 1066          Blocks: 4          IO Block: 1024   regular file
Device: 800h/2048d    Inode: 102672      Links: 1
Access: (0644/-rw-r--r--)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2017-09-11 23:46:24.000000000 +0300
Modify: 2017-09-11 23:46:24.000000000 +0300
Change: 2017-09-11 23:46:24.000000000 +0300
 Birth: -

anyway I kept that in mind when preparing myself to switch to KVM: the configuration is unusual -
64bit kernel (supplied by linode) and 32bit userspace (minimalistic gentoo with very few packages
and default x86 profile)



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Re: Linode discontinuing Xen, migrating to KVM

R0b0t1
In reply to this post by tanstaafl-2
On Tue, Oct 3, 2017 at 6:38 AM, Tanstaafl <[hidden email]> wrote:

> On 10/2/2017, 11:52:21 PM, R0b0t1 <[hidden email]> wrote:
>> As long as your kernel has the appropriate drivers (i.e. you didn't
>> include only the virtualized Xen drivers and left most of the default
>> options intact) it should boot under QEMU/KVM or even on a bare metal
>> system.
>
> Hmmm, something else I just remembered when I noticed my production
> server is running a 32 bit kernel...
>
> A long time ago, maybe 6 or 7 years, something weird happened when
> Linode had some kind of problem (maybe it was another one of their
> maintenance processes, I don't recall), I had a heck of a time getting
> it back up, I finally had to do a full rebuild, and distinctly remember
> changing to a 32 bit kernel during the process, but never changed back.
>
> Do I need to do a full system rebuild to change back to the 64 bit kernel?
>

It shouldn't matter. The virtual processor (just like a real one)
starts up in 16 bit mode and is then set to 32 and then 64 bit mode by
software.

> Also, I haven't played with Linodes 'System Profiles' at all - I was
> thinking I'd just create a new profile, add my Gentoo System Image and a
> swap image to it, but assign the 64 bit kernel, then if it doesn't work,
> switch back. Should I be able to do that without causing any problems to
> the current/working profile?
>

I probably wouldn't use the Linode supplied configurations either, but
it might be a good idea to run diff on yours and theirs to see what
options are different.

R0b0t1.

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Re: Linode discontinuing Xen, migrating to KVM

J. Roeleveld
In reply to this post by tanstaafl-2
On Monday, October 2, 2017 11:17:46 PM CEST Tanstaafl wrote:

> On 10/2/2017, 4:03:37 PM, Tanstaafl <[hidden email]> wrote:
> > On 10/2/2017, 2:39:51 PM, Stroller <[hidden email]> wrote:
> >>> On 2 Oct 2017, at 18:30, Tanstaafl <[hidden email]> wrote:
> >>>
> >>> One thing I do seem to recall is there was somewhere that I had to
> >>> define Xen as the virtualization environment being used, but I can't
> >>> remember where I did that. Was that in the kernel config? If so, their
> >>> tool should (hopefully) handle that change.
> >>
> >> See last lines:
> >>
> >> ~ $ grep -B 25 -ie xen -ie kvm /etc/rc.conf
> >
> > <snip>
> >
> >> # "xen0"           - Xen0 Domain (Linux and NetBSD)
> >> # "xenU"           - XenU Domain (Linux and NetBSD)
> >> ~ $
> >>
> >> This on a Linode host, BTW. They haven't told me I need to do anything,
> >> so I hope I'm ok.
> >>
> >> HTH,
> >
> > Thanks! Yes, at least now I know where that was specified... and since
> > there is nothing there for kvm, I guess you just leave it commented,
> > BUT...
> >
> > yours doesn't appear to be set?? Mine is set to "xenU".
>
> Also, yours shows 12 different choices, mine only shows 8:
>
> ############################################################################
> ## # LINUX SPECIFIC OPTIONS
>
> # This is the subsystem type. Valid options on Linux:
> # ""        - nothing special
> # "lxc"     - Linux Containers
> # "openvz"  - Linux OpenVZ
> # "prefix"  - Prefix
> # "uml"     - Usermode Linux
> # "vserver" - Linux vserver
> # "xen0"    - Xen0 Domain
> # "xenU"    - XenU Domain
> # If this is commented out, automatic detection will be used.
> #
>
> Wonder why that is?

These got updated at some point.
For Xen-guest, I specify:
# rc_sys="xenU"
for KVM guests (got 2 running in the "cloud"):"
# rc_sys=""

If 'rc_sys' is not set, openrc tries to auto-detect.
If it is set, it will not auto-detect and use whatever you specified.

--
Joost

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Re: Linode discontinuing Xen, migrating to KVM

J. Roeleveld
In reply to this post by tanstaafl-2
On Tuesday, October 3, 2017 1:38:46 PM CEST Tanstaafl wrote:

> On 10/2/2017, 11:52:21 PM, R0b0t1 <[hidden email]> wrote:
> > As long as your kernel has the appropriate drivers (i.e. you didn't
> > include only the virtualized Xen drivers and left most of the default
> > options intact) it should boot under QEMU/KVM or even on a bare metal
> > system.
>
> Hmmm, something else I just remembered when I noticed my production
> server is running a 32 bit kernel...
>
> A long time ago, maybe 6 or 7 years, something weird happened when
> Linode had some kind of problem (maybe it was another one of their
> maintenance processes, I don't recall), I had a heck of a time getting
> it back up, I finally had to do a full rebuild, and distinctly remember
> changing to a 32 bit kernel during the process, but never changed back.
>
> Do I need to do a full system rebuild to change back to the 64 bit kernel?

A 32bit userspace can run with either a 32bit or 64bit kernel.
A 64bit userspace can NOT run with a 32bit kernel.

As you currently have a 32bit kernel, I am assuming a 32bit userspace. A 64bit
kernel should not cause issues.

> Also, I haven't played with Linodes 'System Profiles' at all - I was
> thinking I'd just create a new profile, add my Gentoo System Image and a
> swap image to it, but assign the 64 bit kernel, then if it doesn't work,
> switch back. Should I be able to do that without causing any problems to
> the current/working profile?

I have no experience with Linode. Can't they assist with this?

Personally, having a forced change like this would make me reconsider the
hosting partner.

--
Joost

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Re: Linode discontinuing Xen, migrating to KVM

tanstaafl-2
In reply to this post by tanstaafl-2
On Mon Oct 02 2017 13:30:03 GMT-0400 (Eastern Standard Time), Tanstaafl
<[hidden email]> wrote:
> Ok, so just got the notice that Linode is discontinuing their support
> for Xen, and forcing everyone to migrate their VMs to KVM.

Thanks very much to all who replied, two last questions for those who
are using Linode...

First - are you using 'Auto Configure Networking' (is it enabled or
disabled in your Linode options)?

Second, do you have rc_sys defined, or are you using auto-detect (is it
just commented out)?

Thanks again to all who replied...

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Re: Linode discontinuing Xen, migrating to KVM

tanstaafl-2
On Thu Oct 05 2017 18:01:01 GMT-0400 (Eastern Standard Time), Tanstaafl
<[hidden email]> wrote:
> Second, do you have rc_sys defined, or are you using auto-detect (is it
> just commented out)?

Oh - and if I were to change this to auto-detect (comment it out), and
the VM failed to boot, can I specify/change it on the grub boot command
line (still using grub legacy) to recover?

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Re: Linode discontinuing Xen, migrating to KVM

stroller-6
In reply to this post by tanstaafl-2

> On 5 Oct 2017, at 23:01, Tanstaafl <[hidden email]> wrote:
>
> Thanks very much to all who replied, two last questions for those who
> are using Linode…

I've only been using Linode a couple of weeks, and I know nothing about Xen vs KVM.

I just installed Linode's Gentoo image file in a new VM, and started using it, so the below are the defaults.

> First - are you using 'Auto Configure Networking' (is it enabled or
> disabled in your Linode options)?

Enabled.

/etc/resolv.conf and /etc/conf.d/net both say "This file is automatically generated on each boot with your Linode's current network configuration."

I'm not sure I'd dare change it, to be honest.

> Second, do you have rc_sys defined, or are you using auto-detect (is it
> just commented out)?

Just commented out.

Stroller.



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Re: Linode discontinuing Xen, migrating to KVM

tanstaafl-2
On Thu Oct 05 2017 18:53:37 GMT-0400 (Eastern Standard Time), Stroller
<[hidden email]> wrote:
> I just installed Linode's Gentoo image file in a new VM, and started
> using it, so the below are the defaults.

Thanks Stroller,

I had to somehow use my own Gentoo image when I first installed these as
they didn't officially provide any, glad to hear they do now.

>> First - are you using 'Auto Configure Networking' (is it enabled
>> or disabled in your Linode options)?
>
> Enabled.
>
> /etc/resolv.conf and /etc/conf.d/net both say "This file is
> automatically generated on each boot with your Linode's current
> network configuration."
>
> I'm not sure I'd dare change it, to be honest.
Well, I'm not so worried about that since you can always access the VM
using the LISH console to change something like that back.

I'll experiment with this on my Dev VM that isn't mission critical. I
migrated it last night, and it came up just fine, so hopefully my
Production VM will be just as painless.

>> Second, do you have rc_sys defined, or are you using auto-detect (is it
>> just commented out)?
>
> Just commented out.

This is the one I'm worried about - how to change it back if it totally
breaks the ability to even boot.

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Re: Linode discontinuing Xen, migrating to KVM

stroller-6

> On 6 Oct 2017, at 15:31, Tanstaafl <[hidden email]> wrote:
>
>>> Second, do you have rc_sys defined, or are you using auto-detect (is it
>>> just commented out)?
>>
>> Just commented out.
>
> This is the one I'm worried about - how to change it back if it totally
> breaks the ability to even boot.

Detach the drive from the VM, and attach it as /dev/sd[cdefgh] on another VM?

See: Linodes » <name of your node> » Edit Configuration Profile » Block Device Assignment

Also in the dropdowns there is an option for "Recovery -Finnix (iso)".

Stroller.


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Re: Linode discontinuing Xen, migrating to KVM

tanstaafl-2
On 10/7/2017, 12:09:07 AM, Stroller <[hidden email]> wrote:

>
>> On 6 Oct 2017, at 15:31, Tanstaafl <[hidden email]> wrote:
>>
>>>> Second, do you have rc_sys defined, or are you using auto-detect (is it
>>>> just commented out)?
>>>
>>> Just commented out.
>>
>> This is the one I'm worried about - how to change it back if it totally
>> breaks the ability to even boot.
>
> Detach the drive from the VM, and attach it as /dev/sd[cdefgh] on another VM?
>
> See: Linodes » <name of your node> » Edit Configuration Profile » Block Device Assignment
>
> Also in the dropdowns there is an option for "Recovery -Finnix (iso)".

Thanks, yes, I found that in the docs when reading, but was wondering if
there was some lind of grub command-line boot option I could pass (would
be much easier)...

Anyway, wasn't necessary, the migration went perfectly...

1. Change to the 64 bit kernel, reboot

2. Enter migration queue

3. Wait...................................... about 5 minutes

4. Done.

:)

Thanks to everyone who responded!