Moving/merging a filesystem back into /

[Leen Besselink]

On Mon, Dec 02, 2013 at 02:31:23PM -0500, Charles Marcus wrote:
> Hello,
> 
> I'm going to be moving a filesystem around, and was planning on
> using rsync to do it, so like to get some advice from those more
> experienced than I (both using rsync, and moving filesystems)...
> 
> I currently have a system that has a separate /usr on an LVM partition.
> 
> I want to merge this back into the / (root) filesystem.
> 
> This is a production server (mail server, gentoo linux), so I'd
> really like to not brick this thing in the process.
> 
> What would the best arguments to use for making sure that everything
> is preserved properly for a smooth transition?
> 

I have some simple tips:

> Some suggestions on the gentoo list have been:
> 
> -a, or -axAHX, or -apogXx, or -PvasHAX
> 
> or should I go with a combined -apogsvxAHPX ?
> 

I suggest you have a look at the output of rsync --help, it says:

 -a, --archive               archive mode; equals -rlptgoD (no -H,-A,-X)

Clearly some of the ones you mention are already on that list.

There is no need to add them again.

So what is stored in /usr ? Is there also a /usr/src ? or /usr/local that has any content ?

-A can be useful if you have ACLs, lots of systems don't.

-X can be useful if you have extended attributes, lots of systems don't.

-H is for hardlinks, I don't usually see many of them around.

I've not seen a Gentoo system in a long time, but if /usr just contains installed packages
then I think you won't see any of the above. But if you add them, they don't harm. It will
just take more time and maybe use more memory.

For example -H will use more memory if I'm not mistaken. If you don't have enough memory, it might crash.

But I don't think it is usually a problem these days. But if Gentoo builds all the packages in /usr/src andd
lots of source still exist, it might be very large.

If you do have a /usr/src or /usr/local or something like that. Are they on the same filesystem ?

If not, you want -x to prevent them being copied as well.

You can obviously easily check if there is anything else mounted under /usr by checking the mount command and/or /etc/fstab

I've never used -s

I don't see any reason for using -p or -P for partial files, because if copying doesn't succeed you'll probably
just start over. There is no network to worry about.

> Or is all that necessary? Would -a be all I need?
> 
> Thanks for any comments/suggestions...
> 
> ********** OT *********
> 
> If anyone cares to comment on the steps I've settled on, I'd
> appreciate that too:
> 
> 1. Boot off of the latest gentoo LiveDVD
> 
> 2. Mount /
> 
> mount /dev/sda3 /mnt/gentoo/
> 
> There should already be a /usr directory where it was being mounted
> before, right? If not, then I guess I create it with root:root 755
> permissions.
> 
> 3. Mount old /usr to be moved/merged
> 
> vgscan
> vgchange -a y
> mount /dev/vg/usr /mnt/gentoo/oldusr
> 
> 4. Copy /oldusr to /usr
> 
> rsync -a? /mnt/gentoo/oldusr/ /mnt/gentoo/usr/
> 

When using rsync from an other machine, which uses other uids/gids,
I would always recommend to add:

--numeric-ids

> Are the trailing slashes required/important/necessary?
> 

Yes, you need to use them when you are working with directories.

> Which arguments should I use?
> 
> 5. Edit /etc/fstab and comment/remove the /usr line
> 
> nano -wc /mnt/gentoo/etc/fstab
> 
> #/dev/vg/usr       /usr        reiserfs        noatime         0 0
> 
> 6. Unmount mounted filesystems
> 
> umount /mnt/gentoo/oldusr
> umount /mnt/gentoo
> 
> 7. Reboot into new system
> 

Anyway, on most Linux distributions, moving the content of /usr shouldn't be a big event.

Because the system doesn't change the content of /usr it usually just contains programs,
libraries and other files from installed packages.

Don't worry, to much.

If it's a mailserver, what you could do is:

- shutdown
- unplug the network
- do everything you need to do to copy the files and change fstab
- check if everything starts up normally
- plug network back in

If with the check something fails, reboot with the livecd again and fix any problems.

Because the mailserver isn't connected to the network, no mail was lots or bounced.

I assume this is a standalone mailserver that doesn't depend on an external database. A
mailserver shouldn't bounce mail if DNS isn't working for a little while.

Something else you could consider is to not automatically start the server processes and first
check that everything works. Don't forgot to enable them to start automatically again when
everything is done ;-)

> Done?
> 
> -- 
> 
> Best regards,
> 
> */Charles/*

Hope that was useful for you.

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