Ubuntu – How to set up passwordless SSH access for root user


I need to configure a machine so software installation can be automated remotely via SSH. Following the wiki, I was able to setup SSH keys so my user can access the machine without a password, but I still need to manually enter my password when I use sudo, which obviously an automated process shouldn't have to do.

Although my /etc/ssh/sshd_config has PermitRootLogin yes, I can't seem to be able to log in as root, presumably because it's not a "real" account with a separate password.

How do I configure SSH keys, so a process can remotely log in as root on Ubuntu?

Best Answer

Part 1 : SSH key without a password

To set up a passwordless SSH connection for the root user you need to have root access on the server. Easiest method is to temporarily allow root to log in over ssh via password. One way or another you need root access on the server to do this. If you do not have root access on the server, contact the server administrator for help.

On the client (where you ssh FROM)

First make a ssh key with no password. I highly suggest you give it a name rather then using the default

ssh-keygen -f foo

The -f option specifies a file name, foo is an example, use whatever name you wish.

When you are prompted for a password, just hit the enter key and you will generate a key with no password.

Next you need to transfer the key to the server. Easiest method is to use ssh-copy-id . To do this you must temporarily allow root to ssh into the server.

On the server (where you ssh TO)

edit /etc/ssh/sshd_config

sudo nano /etc/ssh/sshd_config

Make sure you allow root to log in with the following syntax

PasswordAuthentication yes
PermitRootLogin yes

Restart the server

sudo service ssh restart

Set a root password, use a strong one

sudo passwd

On the client :

From the client, Transfer the key to the server

ssh-copy-id -i ~/.ssh/foo root@server

change "foo" the the name of your key and enter your server root password when asked.

Test the key

ssh -i ~/.ssh/foo root@server

Assuming it works, unset a root password and disable password login.

On the server :

sudo passwd -l root

Edit /etc/ssh/sshd_config

sudo nano `/etc/ssh/sshd_config`

Change the following :

PasswordAuthentication no
PermitRootLogin without-password

Restart the server

sudo service ssh restart

On the client (Test):

You should now be able to ssh in with your key without a password and you should not be able to ssh in as any user without a key.

ssh -i ~/.ssh/foo root@server

Part 2 : Running commands via sudo without entering a password

You configure sudo to allow you to run commands without a password.

This is answered here in two places:

Of the two, I suggest allowing as few commands as possible (first answer) rather then all commands (second answer).