How to move from one filesystem to another without changing directory structure?

Question

/dev/xvda1 is full so I want to move its contents onto my 30GB udev filesystem.

Filesystem      Size  Used Avail Use% Mounted on
udev             30G  4.0K   30G   1% /dev
tmpfs           5.9G  768K  5.9G   1% /run
/dev/xvda1      7.8G  7.4G     0 100% /
none            4.0K     0  4.0K   0% /sys/fs/cgroup
none            5.0M     0  5.0M   0% /run/lock
none             30G     0   30G   0% /run/shm
none            100M     0  100M   0% /run/user

How can I do that?

Stack: EC2 Ubuntu machine.

Solution 1

Do not use cp to copy large amounts of data.
Use rsync as well, as it can be restarted if it is interrupted. Use the following:

rsync -az -H /path/to/source  /path/to/destination

-a : Archive mode (i.e. recurse into directories, and preserve symlinks, file permissions, file modification times, file group, file owner, device files & special files) <br>
-z : Compress file data during the transfer <br>
-H : Preserve hard links (i.e. copy hard links as hard links)

Edited as pointed by the commenters, I did not see this is your / dir.
If using bash or zsh as shell add:

--exclude={"/dev/*","/proc/*","/sys/*","/tmp/*","/run/*","/mnt/*","/media/*","/lost+found"}

Now it becomes

rsync -az -H --exclude={"/dev/*","/proc/*","/sys/*","/tmp/*","/run/*","/mnt/*","/media/*","/lost+found"} /path/to/source  /path/to/destination 

Otherwise if using different shell, you should do a --exclude statement for every different dir.

Solution 2

In most cases, you wouldn't move the files from one filesystem to another. If you're enlarging the disk in a virtual machine or grabbing more space from the same disk, you'd enlarge the partition containing the filesystem then enlarge the filesystem to fill the partition (which commands to use depends on the partition type and filesystem type). If you're moving to a new disk, it's usually faster and easier to copy the partition as a whole and then enlarge it as above.

In your case, since this is a virtual machine, you'll need to first give it a bigger disk. As noted by Mark Plotnick in a comment, check the AWS guide; there's a web interface to attach a new volume, and there's also a web interface to perform the copy (by creating and the restoring a snapshot).

Note that /dev is not a storage filesystem, it's a filesystem in RAM. Its 30GB free are the maximum amount of data that can be stored there, but that takes a chunk from your RAM, and is lost when you reboot. Once again, do not move any files to /dev, they would be deleted when you reboot.

Comments

[dhag]

The /dev filesystem, of type udev, is not backed by permanent storage. You almost certainly do not want to move / there.

[Mark Plotnick]

Is this a local Xen system or are you using a cloud provider?

[rafaelcosman]

Thanks @MarkPlotnick, I've edited my post to point out that it's on an EC2 machine.

[Mark Plotnick]

You need a larger permanent disk volume. docs.aws.amazon.com/AWSEC2/latest/UserGuide/… . Create a new, larger volume based on a snapshot of this volume, detach the old volume, attach the new volume, use resize2fs.

[roaima]

No point using -z for a local copy.

[Jeff Schaller]

I hope you're not (indirectly) suggesting that they rsync files from / to /dev ? See dhag's comment above

[Hristo Mohamed]

I did not see this is his root, I have editted my post

[rafaelcosman]

Thanks for the quick reply. At the end of the day, I want my directory structure to be unchanged. As in for each file that was formerly at /, I want it to still be at /. Will this get me that?

[Hristo Mohamed]

The contents of /dev, /proc, /sys, /tmp and /run were excluded because they are populated at boot (while the folders themselves are not created), /lost+found is filesystem-specific. If there are files you want to keep at /mnt or /media you can remove them from the list.

[Gilles 'SO- stop being evil']

There's nothing wrong with using cp -ax to copy a whole filesystem. With GNU coreutils, that's the command that's most likely to preserve all “special cases” (permissions, extended attributes, exotic file types, etc.).

[Hristo Mohamed]

Cp does not allow you to restart the copy if something goes wrong. Plus in general not everyone has access to the GNU version!