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kolcon
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Joined: 21 Sep 2007
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PostPosted: Sun Aug 08, 2010 8:50 pm    Post subject: 32bit -> 64bit without downtime Reply with quote

Hello,

I have a server currently running 32bit Gentoo.
Say I would like to migrate it to 64bit (the CPU is capable of it).

Is it possible to do a chroot install? I would like to minimize the downtime.
Or - perhaps - somehow - compile 64bit kernel, reboot (minimal downtime) and then
continue building the chroot?

Thank you

Lubos
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NeddySeagoon
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PostPosted: Sun Aug 08, 2010 9:00 pm    Post subject: Reply with quote

kolcon,

You can't do a 64 bit chroot install while you run a 32 bit kernel.

You also need to swap your toolchain in one go. A mix of 32 bit and 64 bit is horribly broken.
Lastly, the /lib layout is different as 64 bit installs have some 32 bit libs, so they can run 32 bit software.

It will be much less pain, and probably faster, to reinstall
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kolcon
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Joined: 21 Sep 2007
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Location: Europe, CZ

PostPosted: Mon Aug 09, 2010 10:43 am    Post subject: Reply with quote

NeddySeagoon wrote:
kolcon,

You can't do a 64 bit chroot install while you run a 32 bit kernel.

You also need to swap your toolchain in one go. A mix of 32 bit and 64 bit is horribly broken.
Lastly, the /lib layout is different as 64 bit installs have some 32 bit libs, so they can run 32 bit software.

It will be much less pain, and probably faster, to reinstall


OK, I understand. I will postpone the migration to 64bit then, as it would probably not give
any real benefits anyway. Will just wait for new machine and then do it clean.
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neuron
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Joined: 28 May 2002
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PostPosted: Sun Sep 05, 2010 4:20 pm    Post subject: Reply with quote

You can probably setup a generic 64bit build in a virtual machine and move that over afterwards. Then rebuild the system with the right cflags after.
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chithanh
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Joined: 05 Aug 2006
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PostPosted: Sun Sep 05, 2010 6:40 pm    Post subject: Reply with quote

It is possible with minimal downtime if your kernel supports kexec(). But it requires some preparation. Basically the steps are as follows:
  1. Install a 64 bit kernel using crossdev or similar
  2. kexec() to your 64 bit kernel
  3. Build a 64 bit system in chroot
  4. Switch to your new system using busybox switch_root
Steps 2 and 4 need to be done from single user mode. Probably it would be a good idea to exercise all steps in a test environment before applying to a production system.
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Corona688
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Joined: 10 Jan 2004
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PostPosted: Fri Sep 10, 2010 3:44 am    Post subject: Reply with quote

kolcon wrote:
OK, I understand. I will postpone the migration to 64bit then, as it would probably not give
any real benefits anyway. Will just wait for new machine and then do it clean.
I had to sneakernet a disk home recently to fsck it, the 32-bit machine couldn't do so without running out of virtual memory.
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