We've recently set up a new Linux box which is on the same local network as the rest of our machines. We want to allow only the machines on the local network to be able to SSH into the new machine, and I was going to do this by creating ssh keys and disabling password authentication.
What I've done is run ssh-keygen -t rsa -b 4096 on the new machine, copy the contents of the public key and put this in the ~/.ssh/authorized_keys file on one of the machines previously set up.
I've then gone into /etc/ssh/sshd_config on the new machine and have this:
PermitRootLogin no
PubkeyAuthentication yes
PasswordAuthentication no
Those are the only changes I made to this file, and when I try to SSH from the old machine, I get "Permission denied(publickey,gssapi-keyex,gssapi-with-mic)"
If I enable PasswordAuthentication and try to ssh I can log in by entering the user's password, but that's not the goal.
Thanks in advance,
Daniel
If the user you are trying to log in as is root, the directive
PermitRootLogin no
is denying access, regardless the authentication method.
To allow root to log in using keys only, you should set this directive to prohibit-password
I'm working on an embedded board (i.MX6) with a Yocto-based embedded Linux. So far I used Dropbear as SSH server. However, Dropbear doesn't provide an SFTP server, which I need. Therefore I switched from Dropbear to OpenSSH (built it from the standard Poky sources, and installed it via opkg).
However, since then I cannot login to the board via SSH anymore, because the server asks for a password, which I don't know. The only user is root, and it has no password configured (this is still true, because I can log in locally via RS232 without problems). Why does OpenSSH ask for a password? How can I remove that?
I thought that maybe there's a passphrase set in one of the private keys in /etc/ssh:
/etc/ssh/ssh_host_dsa_key
/etc/ssh/ssh_host_ecdsa_key
/etc/ssh/ssh_host_ed25519_key
/etc/ssh/ssh_host_rsa_key
So I did ssh-keygen -p -f /etc/ssh/ssh_host_rsa_key respectively for each of them, but it didn't help.
This is the essential pieces of the sshd_config file:
# grep '^[^#]' /etc/ssh/sshd_config
Protocol 2
PermitRootLogin yes
AuthorizedKeysFile .ssh/authorized_keys
UsePrivilegeSeparation sandbox # Default for new installations.
Compression no
ClientAliveInterval 15
ClientAliveCountMax 4
Subsystem sftp /usr/lib/openssh/sftp-server
Any ideas?
Are you sure that you have debug-tweaks in your IMAGE_FEATURES or EXTRA_IMAGE_FEATURES?
If so, the ROOTFS_POSTPROCESS_COMMAND should include ssh_allow_empty_password(); which in turns should set PermitEmptyPasswords yes in /etc/ssh/sshd_config and /etc/ssh/sshd_config_readonly. That should allow you to use empty passwords with OpenSSH.
If you have "debug-tweaks" in your EXTRA_IMAGE_FEATURES then the password will be blank: this may be ok for development images.
If you want to have some security instead, you can either add a recipe that installs a public key to /root/.ssh/authorized_keys or use the extrausers class in an image recipe or local configuration to set the password.
Backstory: currently running Arch Linux and attempting to authenticate into Github using SSH keys. I have openssh 7.1p1-1 installed as well as git 2.6.4-1.
Problem: After the ssh-agent terminates (system reboot or shell closure), I get the "Permission Denied (publickey)" message when attempting to connect to git using:
ssh -vT git#github.com
Any ideas as to why my identity does not persist? Do I have to add anything special to the ~/.ssh/config or /etc/ssh/ssh_config files?
Thank you for any help you can provide.
After ssh-agent is gone, ssh is no longer aware that id_github exists, so it never tries authenticating with that key. If you want to force ssh to always use that key for github.com, you can add this to ~/.ssh/config:
Host github.com
IdentityFile ~/.ssh/id_github
User git # Handy addition so you can skip the username part in Github URLs
I'm trying to configure my SSH server to require users to have an RSA key. To do this I have the settings in sshd_config set to
RSAAuthentication yes
PubkeyAuthentication yes
#AuthorizedKeysFile %h/.ssh/authorized_keys
and
# Change to yes to enable challenge-response passwords (beware issues with
# some PAM modules and threads)
ChallengeResponseAuthentication no
# Change to no to disable tunnelled clear text passwords
PasswordAuthentication no
and
UsePAM no
Then I do sudo /etc/init.d/ssh restart to restart the server.
This seems to work to some degree, because I included my macs rsa_key and it lets me log in without asking for a password. However when I try to ssh in through a computer that I haven't included the key of, it just prompts me for my password, and then when entered, lets me in.
What am I doing wrong?
I'd say you're not reloading your ssh config correctly. Which Linux distribution/version are you using (assuming you're even using Linux)?
In Ubuntu I usually do:
sudo restart ssh
OR
sudo service ssh restart
Additionally, though not germane to this question - ideally root should not have a password - you should use be using sudo.
I think you also need
ChallengeResponseAuthentication no
UsePAM no
PermitRootLogin without-password
otherwise even if sshd does not ask itself for a password, it will trust PAM and login which will authenticate the user with its password.
While testing, make sure to have another way in in case a problem occurs with SSH...
And make sure you restart your server with /etc/init.d/sshd restart.
When i ssh to a machine, sometime i get this error warning and it prompts to say "yes" or "no". This cause some trouble when running from scripts that automatically ssh to other machines.
Warning Message:
The authenticity of host '<host>' can't be established.
ECDSA key fingerprint is SHA256:TER0dEslggzS/BROmiE/s70WqcYy6bk52fs+MLTIptM.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'pc' (ECDSA) to the list of known hosts.
Is there a way to automatically say "yes" or ignore this?
Depending on your ssh client, you can set the StrictHostKeyChecking option to no on the command line, and/or send the key to a null known_hosts file. You can also set these options in your config file, either for all hosts or for a given set of IP addresses or host names.
ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no
EDIT
As #IanDunn notes, there are security risks to doing this. If the resource you're connecting to has been spoofed by an attacker, they could potentially replay the destination server's challenge back to you, fooling you into thinking that you're connecting to the remote resource while in fact they are connecting to that resource with your credentials. You should carefully consider whether that's an appropriate risk to take on before altering your connection mechanism to skip HostKeyChecking.
Reference.
Old question that deserves a better answer.
You can prevent interactive prompt without disabling StrictHostKeyChecking (which is insecure).
Incorporate the following logic into your script:
if [ -z "$(ssh-keygen -F $IP)" ]; then
ssh-keyscan -H $IP >> ~/.ssh/known_hosts
fi
It checks if public key of the server is in known_hosts. If not, it requests public key from the server and adds it to known_hosts.
In this way you are exposed to Man-In-The-Middle attack only once, which may be mitigated by:
ensuring that the script connects first time over a secure channel
inspecting logs or known_hosts to check fingerprints manually (to be done only once)
To disable (or control disabling), add the following lines to the beginning of /etc/ssh/ssh_config...
Host 192.168.0.*
StrictHostKeyChecking=no
UserKnownHostsFile=/dev/null
Options:
The Host subnet can be * to allow unrestricted access to all IPs.
Edit /etc/ssh/ssh_config for global configuration or ~/.ssh/config for user-specific configuration.
See http://linuxcommando.blogspot.com/2008/10/how-to-disable-ssh-host-key-checking.html
Similar question on superuser.com - see https://superuser.com/a/628801/55163
Make sure ~/.ssh/known_hosts is writable. That fixed it for me.
The best way to go about this is to use 'BatchMode' in addition to 'StrictHostKeyChecking'. This way, your script will accept a new hostname and write it to the known_hosts file, but won't require yes/no intervention.
ssh -o BatchMode=yes -o StrictHostKeyChecking=no user#server.example.com "uptime"
This warning is issued due the security features, do not disable this feature.
It's just displayed once.
If it still appears after second connection, the problem is probably in writing to the known_hosts file.
In this case you'll also get the following message:
Failed to add the host to the list of known hosts
You may fix it by changing owner of changing the permissions of the file to be writable by your user.
sudo chown -v $USER ~/.ssh/known_hosts
Edit your config file normally located at '~/.ssh/config', and at the beggining of the file, add the below lines
Host *
User your_login_user
StrictHostKeyChecking no
IdentityFile ~/my_path/id_rsa.pub
User set to your_login_user says that this settings belongs to your_login_user
StrictHostKeyChecking set to no will avoid the prompt
IdentityFile is path to RSA key
This works for me and my scripts, good luck to you.
Ideally, you should create a self-managed certificate authority. Start with generating a key pair:
ssh-keygen -f cert_signer
Then sign each server's public host key:
ssh-keygen -s cert_signer -I cert_signer -h -n www.example.com -V +52w /etc/ssh/ssh_host_rsa_key.pub
This generates a signed public host key:
/etc/ssh/ssh_host_rsa_key-cert.pub
In /etc/ssh/sshd_config, point the HostCertificate to this file:
HostCertificate /etc/ssh/ssh_host_rsa_key-cert.pub
Restart the sshd service:
service sshd restart
Then on the SSH client, add the following to ~/.ssh/known_hosts:
#cert-authority *.example.com ssh-rsa AAAAB3Nz...cYwy+1Y2u/
The above contains:
#cert-authority
The domain *.example.com
The full contents of the public key cert_signer.pub
The cert_signer public key will trust any server whose public host key is signed by the cert_signer private key.
Although this requires a one-time configuration on the client side, you can trust multiple servers, including those that haven't been provisioned yet (as long as you sign each server, that is).
For more details, see this wiki page.
Do this -> chmod +w ~/.ssh/known_hosts. This adds write permission to the file at ~/.ssh/known_hosts. After that the remote host will be added to the known_hosts file when you connect to it the next time.
With reference to Cori's answer, I modified it and used below command, which is working. Without exit, remaining command was actually logging to remote machine, which I didn't want in script
ssh -o StrictHostKeyChecking=no user#ip_of_remote_machine "exit"
Add these to your /etc/ssh/ssh_config
Host *
UserKnownHostsFile=/dev/null
StrictHostKeyChecking=no
Generally this problem occurs when you are modifying the keys very oftenly. Based on the server it might take some time to update the new key that you have generated and pasted in the server. So after generating the key and pasting in the server, wait for 3 to 4 hours and then try. The problem should be solved. It happened with me.
The following steps are used to authenticate yourself to the host
Generate a ssh key. You will be asked to create a password for the key
ssh-keygen -f ~/.ssh/id_ecdsa -t ecdsa -b 521
(above uses the recommended encryption technique)
Copy the key over to the remote host
ssh-copy-id -i ~/.ssh/id_ecdsa user#host
N.B the user # host will be different to you. You will need to type in the password for this server, not the keys password.
You can now login to the server securely and not get an error message.
ssh user#host
All source information is located here:
ssh-keygen
For anyone who finds this and is simply looking to prevent the prompt on first connection, but still wants ssh to strictly check the key on subsequent connections (trust on first use), you can set StrictHostKeyChecking to accept-new in ~/.ssh/config, which will do what you're looking for. You can read more about it in man ssh_config. I strongly discourage disabling key checking altogether.
Run this in host server it's premonition issue
chmod -R 700 ~/.ssh
I had the same error and wanted to draw attention to the fact that - as it just happened to me - you might just have wrong privileges.You've set up your .ssh directory as either regular or root user and thus you need to be the correct user. When this error appeared, I was root but I configured .ssh as regular user. Exiting root fixed it.
This is trying to establish password-less authentication. So, if you try to run that command manually once, it will ask to provide the password there. After entering password, it saves that password permanently, and it will never ask again to type 'yes' or 'no'.
For me the reason is that I have wrong permission on ~/.ssh/known_hosts.
I have no write permission on known_hosts file. So it ask me again and again.
In my case, the host was unkown and instead of typing yes to the question are you sure you want to continue connecting(yes/no/[fingerprint])? I was just hitting enter .
I solve the issue which gives below written error:
Error:
The authenticity of host 'XXX.XXX.XXX' can't be established.
RSA key fingerprint is 09:6c:ef:cd:55:c4:4f:ss:5a:88:46:0a:a9:27:83:89.
Solution:
1. install any openSSH tool.
2. run command ssh
3. it will ask for do u add this host like.
accept YES.
4. This host will add in the known host list.
5. Now you are able to connect with this host.
This solution is working now......