Messed up etc/fstab on linux instance

Do you have EC2 snapshots?
One way to do this would be to restore EC2 once a snapshot is available.

Another way is to stop the EC2, detach the root volume, mount it on another EC2, and then modify "/etc/fstab".

The process is as follows.

• Stop the instance.
• Detach the target volume by volume.
• Note down the instance ID of the instance in the same AZ.
• Attach the volume to the target instance.
• Check the attached instance.

After attaching the root volume to another EC2, you can confirm that it is attached with the following command.

sudo ls -la /dev/sdf*

Then, create a directory for mounting with the following command.

sudo mkdir /mnt/ebs-check

After creating the directory, mount it.
Device names, etc. may depend on your environment and should be changed as the case may be.

sudo mount /dev/sdf1 /mnt/ebs-check

Once mounted, modify "/etc/fstab".
After the modification is complete, if you can attach the root volume to the original EC2 and start EC2, you should be able to connect.

Please check the following documents for other troubleshooting methods.
https://repost.aws/knowledge-center/ec2-linux-emergency-mode