Attaching and mounting existing EBS volume to EC2 instance filesystem issue

Question

I had some unknown issue with my old EC2 instance so that I can't ssh into it anymore. Therefore I'm attempting to create a new EBS volume from a snapshot of the old volume and mount it into the new instance. Here is exactly what I did:

1. Created a new volume from snapshot of the old one.
2. Created a new EC2 instance and attached the volume to it as /dev/xvdf (or /dev/sdf)

3. SSHed into the instance and attempted to mount the old volume with:

   $ sudo mkdir -m 000 /vol $ sudo mount /dev/xvdf /vol

And the output was:

mount: block device /dev/xvdf is write-protected, mounting read-only mount: you must specify the filesystem type 

I know I should specify the filesytem as ext4 but the volume contains a lot of important data, so I cannot afford to format it with $ sudo mkfs -t ext4 /dev/xvdf. If I try sudo mount /dev/xvdf /vol -t ext4 (no formatting) I get:

mount: wrong fs type, bad option, bad superblock on /dev/xvdf,        missing codepage or helper program, or other error        In some cases useful info is found in syslog - try        dmesg | tail  or so 

And dmesg | tail gives me:

[ 1433.217915] EXT4-fs (xvdf): VFS: Can't find ext4 filesystem [ 1433.222107] FAT-fs (xvdf): bogus number of reserved sectors [ 1433.226127] FAT-fs (xvdf): Can't find a valid FAT filesystem [ 1433.260752] EXT4-fs (xvdf): VFS: Can't find ext4 filesystem [ 1433.265563] EXT4-fs (xvdf): VFS: Can't find ext4 filesystem [ 1433.270477] EXT4-fs (xvdf): VFS: Can't find ext4 filesystem [ 1433.274549] FAT-fs (xvdf): bogus number of reserved sectors [ 1433.277632] FAT-fs (xvdf): Can't find a valid FAT filesystem [ 1433.306549] ISOFS: Unable to identify CD-ROM format. [ 2373.694570] EXT4-fs (xvdf): VFS: Can't find ext4 filesystem 

By the way, the 'mounting read-only' message also worries me but I haven't look into it yet since I can't mount the volume at all.

Thanks in advance!

Answer 1

The One Liner

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🥇 Mount the partition (if disk is partitioned):

sudo mount /dev/xvdf1 /vol -t ext4 

Mount the disk (if not partitioned):

sudo mount /dev/xvdf /vol -t ext4 

where:

• /dev/xvdf is changed to the EBS Volume device being mounted
• /vol is changed to the folder you want to mount to.
• ext4 is the filesystem type of the volume being mounted

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Common Mistakes How To:

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✳️ Attached Devices List

Check your mount command for the correct EBS Volume device name and filesystem type. The following will list them all:

sudo lsblk --output NAME,TYPE,SIZE,FSTYPE,MOUNTPOINT,UUID,LABEL 

If your EBS Volume displays with an attached partition, mount the partition; not the disk.

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✳️ If your volume isn't listed

If it doesn't show, you didn't Attach your EBS Volume in AWS web-console

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✳️ Auto Remounting on Reboot

These devices become unmounted again if the EC2 Instance ever reboots.

A way to make them mount again upon startup is to add the volume to the server's /etc/fstab file.

🔥 Caution:🔥
If you corrupt the /etc/fstab file, it will make your system unbootable. Read AWS's short article so you know to check that you did it correctly.

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-using-volumes.html#ebs-mount-after-reboot

First:
With the lsblk command above, find your volume's UUID & FSTYPE.

Second:
Keep a copy of your original fstab file.

sudo cp /etc/fstab /etc/fstab.original 

Third:
Add a line for the volume in sudo nano /etc/fstab.

The fields of fstab are 'tab-separated' and each line has the following fields:

<UUID>  <MOUNTPOINT>    <FSTYPE>    defaults,discard,nofail 0   0 

Here's an example to help you, my own fstab reads as follows:

LABEL=cloudimg-rootfs   /   ext4    defaults,discard,nofail 0   0 UUID=e4a4b1df-cf4a-469b-af45-89beceea5df7   /var/www-data   ext4    defaults,discard,nofail 0   0 

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That's it, you're done. Check for errors in your work by running:

sudo mount --all --verbose 

You will see something like this if things are 👍:

/                   : ignored /var/www-data       : already mounted 

Answer 2

I encountered this problem too after adding a new 16GB volume and attaching it to an existing instance. First of all you need to know what disks you have present Run

  sudo fdisk -l  

You'll' have an output that appears like the one shown below detailing information about your disks (volumes"

 Disk /dev/xvda: 12.9 GB, 12884901888 bytes   255 heads, 63 sectors/track, 1566 cylinders, total 25165824 sectors   Units = sectors of 1 * 512 = 512 bytes   Sector size (logical/physical): 512 bytes / 512 bytes   I/O size (minimum/optimal): 512 bytes / 512 bytes   Disk identifier: 0x00000000  Device Boot      Start         End      Blocks   Id  System /dev/xvda1   *       16065    25157789    12570862+  83  Linux   Disk /dev/xvdf: 17.2 GB, 17179869184 bytes  255 heads, 63 sectors/track, 2088 cylinders, total 33554432 sectors  Units = sectors of 1 * 512 = 512 bytes  Sector size (logical/physical): 512 bytes / 512 bytes  I/O size (minimum/optimal): 512 bytes / 512 bytes  Disk identifier: 0x00000000   Disk /dev/xvdf doesn't contain a valid partition table 

As you can see the newly added Disk /dev/xvdf is present. To make it available you need to create a filesystem on it and mount it to a mount point. You can achieve that with the following commands

 sudo mkfs -t ext4 /dev/xvdf 

Making a new file system clears everything in the volume so do this on a fresh volume without important data

Then mount it maybe in a directory under the /mnt folder

 sudo mount /dev/xvdf /mnt/dir/ 

Confirm that you have mounted the volume to the instance by running

  df -h 

This is what you should have

Filesystem      Size  Used Avail Use% Mounted on  udev            486M   12K  486M   1% /dev  tmpfs           100M  400K   99M   1% /run  /dev/xvda1       12G  5.5G  5.7G  50% /  none            4.0K     0  4.0K   0% /sys/fs/cgroup  none            5.0M     0  5.0M   0% /run/lock  none            497M     0  497M   0% /run/shm  none            100M     0  100M   0% /run/user  /dev/xvdf        16G   44M   15G   1% /mnt/ebs 

And that's it you have the volume for use there attached to your existing instance. credit