Resolving hostname error

SSH stands for secure shell, and it is a security protocol that provides end-to-end encryption of data. SSH could not resolve hostname is an error message that occurs when the host system fails to resolve the IP address of the remote host provided with the ssh command. Ssh protocol is widely used to provide secure remote shell access.

The ssh command is used to connect to a remote host. The ssh command requires a hostname to connect to, which is then inquired from a DNS(Domain Name System) server that sends the IP address of the remote host the user is trying to login to. If, for some reason, if the hostname is not resolved, then the ssh could not resolve the hostname error message is displayed.

Understanding SSH

Secure Shell is an intermediate protocol that is implemented between the application layer and the transport layer of the Internet protocol stack. It works on top of the TCP protocol, ensuring reliable delivery and data integrity. To connect to a remote shell, use the ssh command and provide the username and the hostname of the remote host you are trying to connect. Public key cryptography is used to authenticate the user. The private key is stored in the user’s host, which provides authentication. The ssh could not resolve hostname is one of the common errors faced while using ssh.

SSH hostname resolution and DNS

The hostname provided in the ssh command has to be resolved to an IP address, i.e., the address of the remote host in computer-readable form. The hostname can be provided in the IP address form example, 192.168.43.89, or a name can be used instead of example.com, for example. A DNS server is used to resolve the hostname to an IP address. The string of characters provided as the hostname in the command is sent to the DNS server, which then, in turn, returns the IP address of the host.

If the host is unable to contact the DNS server or the DNS server doesn’t return a valid IP address in return then, ssh could not resolve the hostname error that occurs. The ssh could not resolve hostname can also happen due to the cached DNS data stored in the system. Frequently used Domain name addresses are stored in cache storage in the host system so that the system doesn’t need to enquire the DNS server every time it makes a request. If the cache data is outdated or the host’s IP has been charged, the cached data becomes useless and can cause problems like ssh could not resolve the hostname.

If you are receiving the ssh could not resolve the hostname error, then a few steps can be employed to resolve and avoid this error message. Consider the given steps to fix the ssh could not resolve the hostname error.

Check the hostname

Most of the basic and simple measures to avoid the ssh could not resolve hostname is to check whether the hostname you are using with the ssh command is correct or not. Using the wrong hostname or domain address might result in a Wrong DNS response or no valid response at all. Check your hostname address for typos and syntax errors of the command. If everything is correct but still getting the hostname does not resolve the error, then employ the following measures.

Clearing DNS Cache

Clearing the DNS cache might also help resolve the ssh could not fix the hostname error. After the DNS cached data is deleted, a new fresh DNS inquiry is sent to the DNS server for each request, which would be beneficial if the IP address of the host is changed. Follow the given steps to clear the DNS cache in Windows.

• Press Windows + R.
• Enter cmd in the serach box and hit enter.
• In the shell Enter the command ipconfig /flushdns.
• The DNS cache is not cleared.
• Try running the ssh command again.

For Ubuntu users, Enter the following command in the terminal to clear the DNS cache manually.

Editing the /etc/hosts file

If you are trying to connect to a remote host using ssh for the first time and getting a hostname error not resolved error in return, try editing the ssh hosts file and entering the username and hostname in the file. Employing the given steps to edit the hosts’ file and fix the ssh could not resolve the hostname error.

• Open the terminal emulator.
• Enter sudo nano /etc/hosts.
• Enter your root password.
• Now in the file, enter the IP address and hostname of your remote host.
• Press ctrl + O to save the file.
• Press ctrl + X to exit nano.
• Run the ssh command again.

SSh could not resolve hostname github.com

The ssh could not resolve hostname error can also show up while using the git version management program. The git uses the ssh while cloning a repository or pushing a remote repository. The issue can be fixed with the following steps.

• Try to ping the github.com using the ping github.com command. If the server responds then try to run the git command again after rebooting the system, it might be a normal network issue.
• If the issue persists, follow the steps mentioned above, such as clearing the DNS cache.
• Run the following command to restart the network manager in linux, which might help resolve the issue.

sudo service network-manager restart

SSH could not resolve hostname Gitlab

Gitlab is another popular open-source platform that is widely used in DevOps operations. “ssh: Could not resolve hostname gitlab.example.com: Temporary failure in name resolution” is the error message that is displayed while logging into the GitLab server. As the message itself suggests, this is a temporary failure in the name resolution, and chances would be resolved automatically after some time. But if the problem persists, follow the steps suggested above to make it work. You could also try adding ssh:// before the git URL to resolve the hostname issue.

git clone ssh://[email protected]:username/This_is_a_demo.git

SSH could not resolve hostname Gitbucket.org

Bitbucket is another open platform used to host git repositories online. The same hostname resolution problem can be encountered with gitbucket.org as with github.com. To resolve this issue, use the suggested methods and configure your .git config file. Open the config file in the .git folder for your project’s main directory. Change the remote directory listing as mentioned below (remove the ssh:// in the config file) and rerun the command.

url = ssh://[email protected] 
//before

url = [email protected]
//after

FAQs on SSH Could Not Resolve Hostname

Conclusion

The ssh could not resolve hostname is a common error that any user can face. It is not that big of an issue. It simply happens when the ssh command fails to resolve the IP address of the provided hostname. In such situations clearing the DNS cache or editing the /etc/host file can help. This article provided you with the necessary measure and solutions to fix this error. In the end, we also mentioned what to do if you are receiving this error while using the git CLI.

To totally unlock this section you need to Log-in

The error/warning defined in the subject of this article usually can be shown while using, for example, the apt-get tool on Ubuntu/Debian Linux distribution. This could happen after we have (finally) decided to change the hostname of our Linux system giving it a better name. Let’s say that wow it’s called test-server because that is we will use it for. Now, a common scenario would be that, after creating a sudo user because we do not prefer not to be root all the time, we start using commands with sudo, but at some point we see a strange error in the output of the commands:

unable to resolve host {your_hostname}: Name or service not known

The command run with sudo without any problem but this error message will be displayed anyway.

The Fix

The root cause of the error is actually related to the hostname changing. Let’s now show how to fix this unable to resolve hostname error. First, check the hostname of your system with hostname command. For example, let’s say that the hostname is test-server.

$hostname
test-server

The hostname is taken from /etc/hostname file.

cat /etc/hostname 
test-server

The same hostname should be listed in the /etc/hosts file as well. But in our case (and basically in all the cases in which this error appears) the new hostname will miss in the /etc/hosts file as you can see in the output below:

127.0.0.1 localhost
The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

Since it is missing from here, the system is not able to figure out the hostname and thus it throws the error sudo: unable to resolve host or unable to resolve host {your_hostname}: Name or service not known while using apt-get.

To fix this, edit this file and add a new line and set the loopback address with the new hostname (or just replace the old hostname with the new one). You can use Vim or Nano to edit files in command line.

127.0.0.1 <hostname>

So now, our /etc/hosts file looks like this:

127.0.0.1 localhost
127.0.0.1 test-server
The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

Again, if the old hostname is still present anywhere in your /etc/hosts file, you should replace them with the new hostname (it is recommended).

Immediately after adding the above mentioned line, sudo: unable to resolve host or unable to resolve host {your_hostname}: Name or service not known errors will disappear.