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[SOLVED]safe to keep $HOME when migrating from x86 to amd64?
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benny1967
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PostPosted: Sat Dec 28, 2013 7:46 pm    Post subject: [SOLVED]safe to keep $HOME when migrating from x86 to amd64? Reply with quote

I currently have / and $HOME on two hard disks. What I want to do is replace the root partition with a SSD I got for christmas (I'd need a much bigger drive for $HOME) and do a clean re-install, moving from x86 to AMD64 while I'm at it.

Now most people say it would be safe to keep my home directory as it is and simply re-mount it to the new root once the transition is finished. (Some even say the same is true for /etc.)
I do understand there can't be much difference with images, audio- or video-files. But is it really, really safe? What about Evolution, for example? Will the 64bit version happily write new mails to the directories created by the 32bit version? Someone mentioned databases (MySQL in particular) needed to be re-done from scratch...

Any experience with this kind of transition? Any warnings?


Last edited by benny1967 on Thu Jan 02, 2014 8:02 pm; edited 1 time in total
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i92guboj
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PostPosted: Sat Dec 28, 2013 8:36 pm    Post subject: Re: Really safe to keep $HOME when migrating from x86 to amd Reply with quote

benny1967 wrote:
I currently have / and $HOME on two hard disks. What I want to do is replace the root partition with a SSD I got for christmas (I'd need a much bigger drive for $HOME) and do a clean re-install, moving from x86 to AMD64 while I'm at it.

Now most people say it would be safe to keep my home directory as it is and simply re-mount it to the new root once the transition is finished. (Some even say the same is true for /etc.)
I do understand there can't be much difference with images, audio- or video-files. But is it really, really safe? What about Evolution, for example? Will the 64bit version happily write new mails to the directories created by the 32bit version? Someone mentioned databases (MySQL in particular) needed to be re-done from scratch...

Any experience with this kind of transition? Any warnings?


In $HOME there should be only data fles. You shouldn't need to worry, even if the transition was from x86 to something entirely different (let's say arm or powerpc). The only exception would be binaries living in $HOME (i.e. if you compile some little tools on your $HOME or if you download binary games or something). And even then, since amd64 can run x86 object code, it would also work as long as you have the relevant emul packages installed.

I have no idea why someone else told you that you will need to re-do your databases... just export them and import them back in your new installation. As an example, let's take the case where you download a backup of your web database to move it to another hosting. In both cases you probably don't even kn ow what architecture the server has or even if it's a real or a virtual machine living in a distributed cluster... As long as it's mysql, you don't need to care about the architecture.
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Hu
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PostPosted: Sat Dec 28, 2013 9:37 pm    Post subject: Reply with quote

I can offer one major counterpoint. Programs should write their data files in an architecture-agnostic way, such that program A on x86 can read files written by program A on mips, amd64, ppc, etc. However, some authors are lazy and write their data files as a direct dump of the in-memory representation, which can vary based on host bitness, endianness, and alignment rules. If you use only programs that are written to represent their data well, you can share $HOME freely.
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i92guboj
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PostPosted: Sat Dec 28, 2013 10:59 pm    Post subject: Reply with quote

Hu wrote:
I can offer one major counterpoint. Programs should write their data files in an architecture-agnostic way, such that program A on x86 can read files written by program A on mips, amd64, ppc, etc. However, some authors are lazy and write their data files as a direct dump of the in-memory representation, which can vary based on host bitness, endianness, and alignment rules. If you use only programs that are written to represent their data well, you can share $HOME freely.


Yes. But, while that can happen, I can't think of an actual example. Nowadays, with the degree of abstraction that toolkits like gtk+ and qt provide for programmers, and the powerful apis we rely on, it would be difficult to find something like that, I guess :roll:
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benny1967
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PostPosted: Sun Dec 29, 2013 12:58 pm    Post subject: Reply with quote

Well, except for movies, photos and songs, what's most important to me is everything stored by Evolution: mails, contacts, etc.

The multimedia files shouldn't be a problem at all. I'll just make sure I'll have a backup of data created by Evolution... just in case.
In German, there's this saying that being frightened to death means dying as well (probably there's a better English equivalent). So let the show begin... :D
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i92guboj
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PostPosted: Sun Dec 29, 2013 1:39 pm    Post subject: Reply with quote

Regarding evolution, well, I've never used it, and I don't know how it works right now. I hope for good that's better than kmail :lol:

But, to answer your question... while migration from x86 to x86_64 shouldn't be a problem (regarding evolution), the change of version can always be a problem in this kind of program. I mentioned kmail because it is well knoww for being personal info destroyer. Upgrading (or what's worse, downgrading) it could sometimes corrupt for mailbox. I tell you this in case the stable version in x86_64 is lesser than the stable version in x86. Again, I know nothing about evolution and I haven't even checked that. If both arches use the same stable version you should be safe, but still, backup :)

In any case, when changing, upgrading or modifying your PIM suite in any way, you should always keep a backup of your personal info somewhere (and by "somewhere" I mean something that's not connected to the PIM itself, because if your only copy is in your GMail account, then it could very well dissapear if your mail client does something strange).
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benny1967
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PostPosted: Sun Dec 29, 2013 5:11 pm    Post subject: Reply with quote

i92guboj wrote:
while migration from x86 to x86_64 shouldn't be a problem (regarding evolution), the change of version can always be a problem in this kind of program. [...] I tell you this in case the stable version in x86_64 is lesser than the stable version in x86.


Aaahh.. that's a good thing to keep in mind, not only WRT evolution. Thanks!
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ppurka
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PostPosted: Mon Dec 30, 2013 7:28 am    Post subject: Reply with quote

Yes, be careful with evolution. Backup the data files - your mails! I doubt the developers themselves use this as their mail client.
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benny1967
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PostPosted: Thu Jan 02, 2014 8:01 pm    Post subject: Reply with quote

Everything went fine, no problems after re-mounting the old $HOME. :)
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