SSH Permission denied (publickey)

Question

I am trying to connect to a Linode (running Ubuntu 12.04 LTS) from my local machine (also running Ubuntu 12.04 LTS)

I have created a private and public key on my local machine and copied my public key to my Linode's authorized_keys file. However, whenever I try to ssh to my Linode I get the error message Permission denied (publickey).

It's not a problem with how ssh is set up on my Linode because I can ssh to it from my Windows machine using key authentication.

In my .ssh directory on my local Ubuntu machine, I have my id_rsa and id_rsa.pub files. Do I need to create an authorized_keys file on my local machine?

EDIT: This is what I get when I run ssh -vvv -i id_rsa [youruser]@[yourLinode]:

debug3: authmethod_lookup publickey
debug3: remaining preferred: keyboard-interactive,password
debug3: authmethod_is_enabled publickey
debug1: Next authentication method: publickey
debug1: Offering RSA public key: id_rsa
debug3: send_pubkey_test
debug2: we sent a publickey packet, wait for reply
debug1: Authentications that can continue: publickey
debug2: we did not send a packet, disable method
debug1: No more authentication methods to try.
Permission denied (publickey).

Answer 1

PubKeyAuthentication

Set up your client

1. Generate your key.

   ssh-keygen
   

2. Configure ssh to use the key.

   vim ~/.ssh/config
   

   Your config file should have something similar to the following:

   Host SERVERNAME
   Hostname ip-or-domain-of-server
   User USERNAME
   PubKeyAuthentication yes
   IdentityFile ./path/to/key
   

   You can add IdentitiesOnly yes to ensure ssh uses the specified IdentityFile and no other keyfiles during authentication. Setting IdentitiesOnly prevents failed authentications from occurring, when ssh would otherwise attempt to login with multiple keys. Setting this is also considered more secure, as you're not leaking information about other keys you have installed, and maintaining separation of your keys between different levels of access.

3. Copy your key to your server.

   ssh-copy-id -i /path/to/key.pub SERVERNAME`
   

   For example, ssh-copy-id -i ~/.ssh/id_res.pub -p 22 [email protected]

Troubleshooting

1. use "-vvv" option
2. Make sure the server has your PUBLIC key (.pub).
3. Make sure your IdentiyFile points to your PRIVATE key.
4. Make sure your .ssh directory has 700 and the files within are 600 permissions.
   • ssh-keygen will create files and directories for you with the proper permissions
5. tail -f /var/log/auth.log (on the server) and monitor errors when you attempt to login
6. If you have many key files, try IdentitiesOnly yes to limit the authentication to use the single, specified key.

Answer 2

Sometimes the issue comes from permissions and ownership. For instance, if you want to log in as root, /root, .ssh and authorized_keys must belong to root. Otherwise, sshd won't be able to read them and therefore won't be able to tell if the user is authorized to log in.

In your home directory:

chown -R your_user:your_user .ssh

As for rights, go with 700 for .ssh and 600 for authorized_keys

chmod 700 .ssh
chmod 600 .ssh/authorized_keys

Answer 3

The problem I had was it was using the wrong keys on the client. I had renamed id_rsa and id_rsa.pub to something else. You can either rename them back to their default, or when you issue the ssh command, use it like this

ssh -i ~/.ssh/private_key username@host

Answer 4

You don't need authorized_keys on your client.

You must tell the ssh-client to actually use the key you generated. There are several ways to do that. Just for testing type ssh -vvv -i .ssh/id_rsa [youruser]@[yourLinode]. You will have to provide your passphrase every time you want to connect to the server.

If that worked you can add the key to the ssh-agent with ssh-add .ssh/id_rsa (you will have to provide the passphrase only once for this and it should work as long as you don't logout/reboot)

Answer 5

Also check value of PasswordAuthentication in /etc/ssh/sshd_config and if it's no change it to yes. Don't forget to restart ssh service after that.

Answer 6

Another possible cause could be with the AllowedUsers configuration in /etc/ssh/sshd_conf. NOTE: the list is space delimited (not comma delimited) as I learned the hard way.

AllowUsers user1 user2 user3

Answer 7

I ran into this issue recently with my web server.

I typically keep a list of authorized keys on all my servers in ~/.ssh/authorized_keys2. From my experience, sshd will look for ~/.ssh/authorized_keys or ~/.ssh/authorized_keys2 by default.

In the case of my webserver, the /etc/ssh/sshd_config had this line

AuthorizedKeysFile    %h/.ssh/authorized_keys

instead of

AuthorizedKeysFile    %h/.ssh/authorized_keys2

I applied the latter, restarted my ssh daemon, and solved my problem logging in with ssh using my pubkey.

Answer 8

Also make sure that the user's home directory (on the server) actually belongs to the user ssh'ing into (was set to root:root in my case).

Should have been:

sudo chown username:username /home/username;

Answer 9

The following method might work if you can access machineA and machineB independently (e.g. from machineC).

If ssh-copy-id is not working, password authentication could be disabled. The following is a workaround.

Having machineA's public key in machineB's authorized keys (i.e. ~/.ssh/authorized_keys) will allow you to ssh from machineA. This also applies to scp.

After generating the key pairs using: ssh-keygen

On machineA, execute cat ~/.ssh/id_rsa.pub

Sample output:

ssh-rsa AAAAB3NzaSGMFZW7yB anask@mahineA

Copy the printed key (⌘ Command+C, or CRTL+C) then add it to the ~/.ssh/authorized_keys file on machineB.

For example, execute the following on machineB:

echo 'ssh-rsa AAAAB3NzaSGMFZW7yB anask@mahineA' >> ~/.ssh/authorized_keys

Answer 10

Works on Ubuntu 16.04 as well.

The issue is within sshd_config file

Here is the ULTIMATE solution:

Log as as a root to you Ubuntu server

vi /etc/ssh/sshd_config

Now go to very bottom and change the value from "no" to "yes".

It should look like this:

Change to no to disable tunnelled clear text passwords

PasswordAuthentication yes
service sshd reload

to take effect.

Now you can simply a key using following command from your LOCAL machine (aka laptop etc)

So in order to open a new terminal window and NOT log into server, simply use this command:

ssh-copy-id john@serverIPAddress

(Replace john with your username).

you should be good to go

Answer 11

I my case, the client is ubuntu 14.04lts, the server was win 2012 server running cygwin. I was using 'ssh [email protected]', when the 2012 server directory in cygwin was /home/Administrator. So it was case sensitive, when I tried 'ssh [email protected]' (note the capital A on Administrator) then it worked fine.

An error message like 'user not found' would have led me to the solution a lot quicker than 'Permission denied (publickey,keyboard-interactive)'.

Answer 12

I had the same issue when copying a regular user's (e.g. johndoe) public key from a cPanel Centos system over to an Ubuntu server on AWS. As suggested by gertvdijk above, I checked /var/log/auth.log and sure enough it said Authentication refused: bad ownership or modes for directory /home/johndoe. Turns out I had wrongly 777'ed /home/johndoe when trying to set /home/johndoe/public_html as the default virtualhost Document Root for apache2 (that's not needed for that task either).

See also the answers here and here

The server only needs to have the public key in .ssh/authorized_keys and the client (computer you're working on) needs to have the private key (.pem, or if using SFTP with Filezilla, .ppk)

Answer 13

Some people wondering may have set up ssh access to be key only on the root account then created a new user and not realised they need to

ssh root@your-ip-address

rsync --archive --chown=[user]:[user] ~/.ssh /home/[user]

logout

Then try again. Replace [user] with your new user account.

This is common when setting up a new server on DigitalOcean when you've used ssh-keys on setup.

https://www.digitalocean.com/community/tutorials/initial-server-setup-with-ubuntu-18-04

Answer 14

Owner permission for the ~/.ssh directory, should contain your username.

chown -R $USER:$USER /home/$USER/.ssh

Note: Make sure $USER is your correct username (not root).

Answer 15

If all else failed, check that your login user belongs to the ssh's AllowedGroup. That is, your users is a member of the group shown at the following line in /etc/ssh/sshd_config on the server:

AllowGroups ssh #Here only users of 'ssh' group can login

Answer 16

For those Putty users like me who came to this thread, you may also get this error if you forgot to add user user@Ip !

Others being permission on key file chmod to 600)

ssh 1.1.1.1 -i /path/to/.pem file 
Permission denied (publickey).`

ssh [email protected] -i /path/to/.pem file 

Answer 17

This is what worked for me, the fix is not mine but I would rather write it down here in case someone else has the same problem.

The original author posted it here: digital-ocean-public-access-key-denied

sudo nano /etc/ssh/sshd_config

Replace this

UsePAM yes
IgnoreUserKnownHosts no
PasswordAuthentication no

With this

UsePAM no
IgnoreUserKnownHosts no
PasswordAuthentication yes

Save the file and restart ssh

reload ssh

ssh should work now asking for a password

Answer 18

I had the same problem as described in the question. The output from executing ssh -vvv -i id_rsa [youruser]@[yourLinode] on the client machine was similar to that described in the question. I checked all the file and directory permissions as advised in the other answers, and they were correct.

It turned out that when copying the generated file id_rsa.pub to the server machine, as file ~username/.ssh/authorized_keys, I'd accidentally omitted the word ssh-rsa from the start. Adding it solved the problem.

Answer 19

I had added a wrong key to the server. Because I did not use the command with an option to specify a certain key it added the standard key-file.

Make sure you did use ssh-copy-id -i CORRECT_KEY.pub

This wrong key worked great with one client, because this client also had this key. But when trying to connect with another client to the same server it obviously failed.

Also, which might be interesting is that you get more logging with ssh -vv instead of just the single -v.

Answer 20

Another causes for this error are:

1. Incorrect user in ssh -i id_rsa [user]@[yourLinode]
2. Outdated SSH RSA key. OpenSSH v8 deprecated RSA algorithm by default. Regenerate your keys with: ssh-keygen -t ed25519 -f ~/.ssh/your.key -C "My key"

This might be the case especially if you're getting the possible debug warning:

debug1: send_pubkey_test: no mutual signature algorithm

Here is the good article that describes possible issues for this error: https://aws.amazon.com/premiumsupport/knowledge-center/ec2-linux-fix-permission-denied-errors/

Other references:

1. https://www.ssh.com/academy/ssh/keygen#ssh-keys-and-public-key-authentication
2. https://confluence.atlassian.com/bitbucketserverkb/ssh-rsa-key-rejected-with-message-no-mutual-signature-algorithm-1026057701.html

Answer 21

In my case the issue was caused by copying over an .ssh directory from an older machine. Turns out that my older SSH config was using DSA keys which have since been deprecated. Switching to a new pair of keys, this time RSA-based, solved the problem for me.

Answer 22

In general the quickest way to understand the reason of refused SSH connections is to inspect the SSH server log (assuming you can access the log without the tested SSH connection):

sudo systemctl status sshd

One possible reason is a move of the connecting client to a new subnet (ISP etc.) combined with a very restrictive filter set up in /etc/ssh/sshd_config, that requires not only a specific pre-defined user name, but also a connection from a pre-defined IPs range:

$ cat /etc/ssh/sshd_config | grep Users
AllowUsers <user>@1.2.3.4/16