Locked out of EC2 ubuntu instance because of /home perms

Question

I was showing my kids some basic things about directory permissions on an EC2 ubuntu instance, and did this

$ sudo chmod 700 /home

Then demonstrated that I could no longer cd to my home directory because permission was denied.

Then I inadvertantly disconnected from the EC2 instance. Now I cannot log back in because the sshd on the ubuntu side cannot access my /home/ubuntu/.ssh/authorized_keys file. I've tried to think about workarounds, but I'm out of ideas.

I am prepared to delete and recreate the entire instance, but would much rather salvage this one if possible. Any ideas?!

Create a new instance, mount the EBS instance as a data disk, change permissions. — Tim, Jun 13 '18 at 22:29
With that suggestion Fixee can work it out and post an answer. — Tim, Jun 14 '18 at 00:11
I'm an experienced *nix admin, but new to EC2. It took me about 30mins to figure out (aka google) the steps Tim outlined above, which worked perfectly. — Fixee, Jun 14 '18 at 03:50

score 7 · Accepted Answer · answered Jun 14 '18 at 03:49

Following Tim's suggestion:

I clicked Launch Instance to create a new instance. I just took whatever the first AMI was listed (some Amazon version of Linux) and created it with defaults, using a keypair I had already on hand.

I then clicked on Volumes and detached the EBS volume from my hosed machine. This took about 30 secs. Then I selected Attach Volume and I attached it to the new instance as /dev/sdf. Then I sshed into the new instance.

In the new instance I typed

$ sudo mkdir /caribou
$ sudo mount /dev/sdf1 /caribou
$ cd /caribou
$ sudo chmod 755 home

That repaired the /home dir permissions.

I then went back to the EC2 console, detached the EBS volume from the Amazon instance and re-attached it to my original Ubuntu instance as /dev/sda1. Then I started the old instance and logged in, with everything fixed.

Took 30 mins including time to figure out all of the above. Thanks to Tim.

Thanks for taking the time to post how you fixed it, instead of just moving on. — trueCamelType, Jun 14 '18 at 03:52
Welcome. I figured with that little tip you'd work it out, and I didn't have time to write a full answer. — Tim, Jun 14 '18 at 04:47

score 0 · Answer 2 · answered Jun 13 '18 at 22:21

0

I'm not sure if EC2 has this option (it should), but if you haven't disabled root login completely, then open a console session on your instance through EC2 website, log in as root, restore readable permissions and you should be fine.

answered Jun 13 '18 at 22:21

I searched around but cannot find a way to login to my EC2 instance as root. – Fixee Jun 14 '18 at 03:02

Locked out of EC2 ubuntu instance because of /home perms

2 Answers2