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I have an Amazon EC2 instance that has two EBS drives associated with it: an 8 GB drive at /dev/sda1, and a 20 GB drive at /dev/sdf. I didn't set this up so I'm not sure why this instance needs two drives of those sizes.

I'm trying to figure out which of these two EBS drives contains the root (/) volume. (My goal is to disconnect that drive and attach it to another instance, where I can gain access to a key file I need at /home/ec2-user/.ssh/authorized_keys, per this excellent answer.)

How can I tell? (What is /sda1 and /sdf?)

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Just do a df -h. This will tell you if the 8G disk is mounted on / or the 20G one. Then just go to the EC2 web console and detach the disk.

"sda" term us usually used for SCSI drivers. I suggest you to read up a bit about Linux device files. It'll help you a lot.

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First, lets find the root device (probably it is /dev/sda1) with mount command. You will see your disk device with corresponding line where "on" is /.

Then you shoudl go to the AWS management console, EC2 section, find your instance, scroll down to the Block Devices section, then you'll see attached EBS Volumes to the intance and their IDs. Using this data you can find your Volume by its ID in the Volumes section.

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It is almost certainly the one with the numeric subscript, as this is a general indicator of a boot volume (being a partition), presumably to prevent further partitioning but possibly just as likely for bootloader purposes (so grub is not easily broken?).

Use a snapshot, rather than the actual volume.

We are frequently cleaning up volumes ($$$) that have not been terribly well documented, and mounting them to an arbitrary instance for an investigation is often required. I'll admit I use Webmin for this from time to time as it is good for poking around. It would be really good if we could mount to the console in a similar fashion. I'm not lazy, it's hard work, and frought with risk.

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  • No, I don't think that's reliable. Both for this questioner and for a new instance launched recently the root seems to typically be /dev/sda1: in fact the root is the only one with a partition number.
    – poolie
    Mar 21 at 0:53
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    Quite right, I must have been tiired. / tends to be on the boot volume.
    – mckenzm
    Mar 23 at 7:40

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