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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?

marked as duplicate by Panther, karel, sudodus, Eric Carvalho, Fabby Aug 24 '17 at 8:26

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • 4
    If you automate installation from a central machine, you can limit the scope of the key so it will only be accepted from the given host. Simply prefix the line in authorized_keys with from="host.ip.goes.here" ssh-rsa [...] – Egil Mar 23 '12 at 10:03
  • At the end of the day, this question has a poor title. The user can already log in via ssh with a key without a password but now wants to run sudo without a password. I revised the answer to address both issues as this question is linked as how to generate a paswordless ssh key (due to poor title). – Panther Aug 23 '17 at 17:30
up vote 46 down vote accepted

EDIT bodhi.zazen This answer had some serious issues and I am attempting to re-write the answer to resolve the problems with the original 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 ie 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 ---

ON THE SERVER, 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

--- Done on server ---

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

--- DONE ON SERVER ---

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.

From the client

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:

How do I run specific sudo commands without a password?

How to run sudo command with no password?

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

  • @Ashimema - so you make a key ? Where did you make the key ? On the server ? so how does the client machine get the key ? On the client? so how does the key get to the server ? The "proper" ie easiest method is to make the key on the client machine (does not require root) and use ssh-copy-id to transfer the key to the server. – Panther Aug 22 '17 at 18:27
  • That escalated fast. Personally, I'm not impressed by the complete rewrite from a number of angles but as I'm not a regular contributor here anymore I'm really not in the frame of mind for further trolling. Thank you for linking to sudo -i information, it was an interesting read. – Ashimema Aug 22 '17 at 20:14
  • Way to remove lots of helpful comments – Ashimema Aug 22 '17 at 20:15
  • 'Make a key'.. original questions clearly stated they had already made a key and linked to documentation on how. – Ashimema Aug 22 '17 at 20:15

You are confusing two different things:

passwordless log is used to make sure that people can't log into your system remotely by guessing your password. If you can ssh username@machine and connect without a password, this is set up correctly, and has nothing else to do with this.

sudo is used to permit a normal user account to do something with super user permissions. This does require the user to type their password. This happens whether you are connected remotely (via passwordless or password-protected SSH) or are local on the machine. You are trying to set sudo to not ask for your password, which is not recommended, but you can learn how to do that via an answer like https://askubuntu.com/a/74083/6161

Note to future readers of this answer:

My above answer does not answer the original poster's actual question, it describes what you should do instead. If you really want to allow remote connections directly to the root account, you need to enable the root account (see my comment below). Again, let me say DO NOT allow remote remote log-ins to your root account.

  • 2
    You're misunderstanding me. I know the difference between SSH and sudo. The problem is that I'm unable to ssh using root@machine. Using my "normal" account and adding it to my sudoers file would accomplish the same thing, but I was trying to do it solely through SSH. This is possible in Redhat based distros. I take your answer to mean this is not possible in Debian based distros. – Cerin Mar 22 '12 at 19:58
  • @Cerin Ah - you want to enable root log-in askubuntu.com/q/44418/6161 Again, this is almost always a bad idea, especially when you're allowing external connections. But, the link in the comment describes how to do it. – David Oneill Mar 22 '12 at 20:40
  • Thanks. Since my goal is automated software installation, does it matter whether I add a non-root user to sudoers, or allow root log-in? There both potential security concerns, but one of them is necessary. – Cerin Mar 23 '12 at 0:22
  • 2
    sudo provides more fine-grained control. For instance, you could allow the non-root user to run apt as root without giving a password, but not arbitrary commands. Since your goal is automated software installation, you should use the least privileged solution to your goal. – Egil Mar 23 '12 at 9:54
  • @Cerin Yes, it does matter. Beyond what Egil pointed out, askubuntu.com/q/16178/6161 is a whole discussion of why logging in a root is a bad idea. – David Oneill Mar 23 '12 at 17:04

PermitRootLogin controls whether the user named "root" (to be precise: any user with UID 0) is allowed to login. If you're logging as root, you do not need sudo to perform privileged tasks.

On the other hand, if you to login on a user account and use sudo without a password, you must configure the sudoers file without having to fiddle with /etc/ssh/sshd_config. See How to make Ubuntu remember forever the password after the first time

Q. Login to remote host as root user using passwordless SSH (for example ssh root@remotehost_ip)

A. In order to login to remote host as root user using passwordless SSH follow below steps.

1st Step:
First you have to share local user's public key with remote host root user's authorized_keys file. There are many ways to do so, here is one example.

https://www.digitalocean.com/community/tutorials/how-to-set-up-ssh-keys--2

Or you can simply copy paste your public key content to remote host root user's authorized_keys file.

2nd step:
Configure ssh to permit passwordless login in remote host. Login to remote host and edit /etc/ssh/sshd_config file then restart ssh service. Do not forget to comment out "PermitRootLogin yes".

#vim /etc/ssh/sshd_config
PermitRootLogin without-password
StrictModes no

#service ssh restart

Comment out #PermitRootLogin yes

3rd step:
Test you connection from your local machine using user whose public key is shared earlier.

$ssh root@remotehost_ip
  • 1
    Turns out StrictModes no is important on some systems – David Okwii Feb 13 '17 at 13:32

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