Curl error 6 couldn t resolve host

As Linux users continue to skillfully nurture and grow their user experience, they soon realize that they become more performant and productive while in the Linux command-line environment.

The Linux OS environment exposes its users to terminal-based tools like Curl for a non-interactive download and upload of targeted network/internet-based files, which is similar to the Wget utility and both share some similarities in their implementation and functionalities.

The primary role of the Curl utility as highlighted on its manual page is to transfer a targeted URL.

$ man curl 

It supports numerous protocols with the common ones being FTP, FTPS, HTTP, HTTPS, SCP, SFTP, SMTP, and SMTP.

The Curl command syntax is as follows:

$ curl [options / URLs]

We can show its implementation by using it with a random URL.

$ curl https://google.com -o linuxshelltips.txt

In the above command, Curl’s findings from accessing the highlighted URL are saved in the succeeding text file.

curl: (6) could not resolve host Error

Mostly, such an error occurs when there is an issue with a Linux server’s DNS resolver. A Linux administrator will categorize/define this challenge as a server management service issue.

This error is likely to take several forms when the curl command is executed from the Linux terminal and the most popular ones include:

• curl: (6) could not resolve host: domain_name.extension; Name or service not known
• curl: (6) could not resolve host: domain_name.extension e.g. linuxshelltips.com
• curl: (6) could not resolve host: application

Now that we have highlighted the primary reason that might be behind the stated curl command error during its execution on a Linux terminal, it’s time to fix the problem.

Solution 1: Missing Working DNS Nameserver

A nameserver is basically a bridge between a working/purchased domain name and the IP address of a server. When you purchase or subscribe to a domain name, and before you use/link this domain name to your remote Linux server, you need to configure a DNS nameserver. A DNS nameserver enables a user to use a domain name to access a remote server instead of using its IP address.

On your Linux server/machine, the file /etc/resolv.conf is responsible for the DNS nameserver entries auto-generated by NetworkManager.

$ sudo nano /etc/resolv.conf

This file can hold more than one DNS nameserver entry. As you might have noted, the syntax for adding a DNS nameserver entry in this file should resemble the following:

nameserver   IP.ADDRESS

For instance, if you were to add Google public nameservers to this file, it would look like the following:

nameserver   192.168.100.1
nameserver   8.8.8.8
nameserver   8.8.4.4

If you are using a private DNS nameserver, add it to the /etc/resolv.conf file. Update or reboot the system if possible and the host should start resolving.

Solution 2: Curl Syntax Errors

Make sure the curl command execution adheres to its correct syntax usage. A syntax error can arise from something as simple as the misuse of an escape sequence (/) or an illegal spacing on the URL.

The curl: (6) could not resolve host error in Linux primarily relates to wrongful/missing DNS nameserver setup or a random syntax error that can be scanned and fixed.

Are you curious to know why does the error ‘curl (6) could not resolve host ubuntu’ appear?

Usually, such curl errors happen when there are problems with DNS resolvers on the server.

At Bobcares, we often get requests from our customers to fix curl (6) could not resolve host Ubuntu as part of our Server Management Services.

Today, let’s discuss why this error occurs and see how our Support Engineers fix it.

What is curl (6) could not resolve host?

Many of our customers have experienced this error ‘curl (6) could not resolve host’ while trying to connect to a webpage from the terminal.

This error mainly occurs due to a wrong DNS set up or bad settings on the server.

Also, we’ve seen this error appearing in different ways which include.

1. curl: (6) Could not resolve host: application
2. curl: (6) Could not resolve host: domain.com
3. curl: (6) Could not resolve host: google.com; Name or service not known

This essentially means the server was not able to connect to the remote host.

How we fixed the error curl (6) could not resolve host in ubuntu

At Bobcares, where we have more than a decade of expertise in managing servers, we see many customers face problems while managing a server.

Now, let’s see the major reasons for curl errors and how our Support Engineers fix this error.

1. Missing working DNS nameserver

Sometimes, users may receive a problem when trying to install packages like wget, apt-get not being able to resolve hosts.

For example, when executing a command apt-get install wget.

Users may get an error as curl#6 - "Could not resolve host: repo.xxx.com; Unknown error"

This mainly occurs when we don’t have nameservers in the /etc/resolv.conf

So, we added the following line in the file.

nameserver 8.8.8.8

Then, this fixed the error and the host started resolving.

2. Syntax error

Recently, one of our customers had a problem while executing the command curl on his terminal. He used the command as below,

curl -X 'GET https://www.mywebsite.com/Web2/PDF.aspx?page=1' 

Also, the error said Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.119 Safari/537.36 OPR/51.0.2830.26'
curl: (6) Could not resolve host:

On checking, our Support Engineers found that the error was due to the incorrect syntax used to access the website.

So, we corrected the syntax as below. This happened as he had included space after one of the / escape sequences.

curl -X GET https://www.mywebsite.com/Web2/PDF.aspx?page=1/

Similarly, an error happened when running the following command

curl -i -H 'Content-Type: application/json' -d '{"Code":"FR","Name":"France"}' http://127.0.0.1:8080/countries

The error said Curl: (6) Could not resolve host: application.

This error was also due to the syntax error in the command. Thus, we resolved this problem editing like this in windows:

"{/"Code/":/"FR/"}"

In another case, we corrected it by deleting an extra space from the command.

curl -H Content-Type:application/json ~

Finally, this fixed the error.

[Need more help to solve curl error?- We’ll fix it for you.]

Conclusion

In short, an error curl (6) could not resolve host on ubuntu happens due to syntax error or due to the wrong DNS set up. Today, we saw how our Support Engineers assisted our customers to solve this error.

var google_conversion_label = «owonCMyG5nEQ0aD71QM»;

{
    "token_type": "Bearer",
    "expires_in": 518399,
    "access_token": "eyJ0eXAiOiJKV1QiLCJhbGciOiJSUzI1NiIsImp0aSI6Ijk0MWU3Y2Q2Y2I1ZTEyYmYyYzAzYTIzY2I1YWM5YjY3YjI0MmU2NTUwOWRhODVlZTMxNzc3MjIwODA3ZTA2ZGY1YWIwYjMzNDg2MDA2MTZlIn0.eyJhdWQiOiIxIiwianRpIjoiOTQxZTdjZDZjYjVlMTJiZjJjMDNhMjNjYjVhYzliNjdiMjQyZTY1NTA5ZGE4NWVlMzE3NzcyMjA-rkLpvJhuju4Qlo0QNjsXUUHXq6GyqqiQTNa2d0IUsWdAOSLsy1bMu4Z2ga_Jj1L1ThwbDOfy7kE4_5SDfKKIyKXO_-iw",
    "refresh_token": "L8p2NAqRZfi1fP1XyO3NW36dCqa6HZJWgNKkuR8IMz2LJe5711nRHPMP734caln1+8m+GC6K79yTjRjru01iR7LKP1CCseixQ8mkzXWZb+roQv32qdkXVSeCzObecOI2ZWq+l1KNs12NA3KIZJ4bS0N2rOYxlw3KTNx55uydH13vmanbeXIpym0ha8op0M9s9HvwPc+dJUhjL20JzDGCcyuhciGIe6CTKyBuqi4dNA8tIeALLPSSqtvd0QsRWCWTVBL72RVeEeIq/4kFppE="
}

 $http = new Client;

            $response = $http->post('Project.local/oauth/token', [
                'form_params' => [
                    'grant_type' => 'password',
                    'client_id' => 1,
                    'client_secret' => 'xKqNbzcXyjySg20nVuVLw5nk5PAMhFQOQwRTeTjd',
                    'username' => $userobject['email'],
                    'password' => $userobject['password'],
                    'scope' => '',
                ],
            ]);

I have a CentOS 7.3 machine that is a guest running on Oracle VirtualBox. The host is a Windows machine. I can ping 8.8.8.8 from the Linux server. The Linux server can ping itself by its hostname ping coolvm. As root I recently did a yum -y update command. That is when curl stopped working. FQDNs will not resolve.

If I try this:

curl -v http://www.google.com

I get this error:

• Could not resolve host: www.google.com; Unknown error
• Closing connection 0 curl: (6) COuld not resolve host: www.google.com; Unknown error

The commands nslookup, dig and host have not been installed. I cannot install new Yum packages because I get an error related to host resolution («Resolving time out»).

The /etc/resolv.conf file looks like this:

# Generated by NetworkManager
search localdomain
nameserver 8.8.8.8
nameserver 8.8.4.4

I tried rebooting the host machine (and thus the guest too). But that did not help me. Browsing the internet has not changed.

The interface for the main NIC in /etc/sysconfig/network-scripts/ has DNS server stanzas that have worked in the past. The interface file is standard and complete. I have not changed it since the yum -y update command.

How can I get FQDNs to resolve? I want to use the Lynx command. My repositories rely on FQDNs to resolve. I cannot use yum to install packages.

Update. I ran this command:

cat /etc/nsswitch.conf | grep -i hosts

I saw this:

#hosts:   db files nisplus nis dns
hosts:    files dns myhostname

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Error: Error downloading packages: Curl error (6): Couldn’t resolve host name for https://mirrors.fedoraproject.org/metalink?repo=updates-released-f25&arch=x86_64 [Could not resolve host: mirrors.fedoraproject.org]

$ sudo dnf install python

When installing python package, this error is raised (Curl error (6): Couldn’t resolve host name for https://mirrors.fedoraproject.org/metalink?repo=updates-released-f25&arch=x86_64)

How to resolve could not resolve host name issue?

Try running this commands

$ sudo dnf clean all

$ sudo dnf upgrade

Check whether output of the upgrade command is ‘Error: Failed to synchronize cache for repo ‘fedora»

Try ping command for host mirrors.fedoraproject.org

$ ping mirrors.fedoraproject.org 

Output:

ping: mirrors.fedoraproject.org: Temporary failure in name resolution

Try few times if ping is not working and displayed as above and instead of getting reply.

PING wildcard.fedoraproject.org (67.219.144.68) 56(84) bytes of data.
64 bytes from 67.219.144.68 (67.219.144.68): icmp_seq=1 ttl=50 time=367 ms
64 bytes from 67.219.144.68 (67.219.144.68): icmp_seq=2 ttl=50 time=307 ms

Try upgrade command also few times if not working, sometimes connection with host ‘mirrors.fedoraproject.org’ might be temporarily failed.

$ sudo dnf upgrade

Output:

Upgrades all the packages.

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Posted on Sunday, July 27, 2014 by nayana

After you installed Fedora, you may face this issue while updating the system or a any specific application. Any also while try to install new application using Terminal. There are few things you have to do to fedora before you start to work otherwise it will trouble you always.

Today I’m going to treat for these symptoms
1. curl: (6) Could not resolve host
2. curl: (6) Could not resolve host: google.com; Name or service not known
3. nolookup not working
4. Firefox doesn’t have internet
5. Couldn’t resolve host when installing/updating yum packages
6. Very Slow DNS Lookup
7. Very slow to load web pages in web browser.

Here is the step by step solution.

1. Most of the issues occur because of the IPV6 internet connection in the Fedora. So first we have to disable IPV6 totally. here what you have to do

• Open Terminal
• Type su and enter to log in as the super user
• Enter the root password
• Type cd /etc/modprobe.d/ to change directory to /etc/modprobe.d/
• Type vi disableipv6.conf to create a new file there
• Press Esc + i for insert data to file
• Type install ipv6 /bin/true on the file to avoid loading IPV6 related modules
• Type Esc + : and then wq for save and exit
• Type reboot to restart fedora
• After reboot open terminal and type lsmod | grep ipv6 
• If no result, it means you properly disabled IPV6

2. Then you have to disable the IPV6 DNS look-up in your Firefox browser. For that you have to go true one of my step by step tutorial. below I mention the link. But remember to comeback here to continue rest of the tasks.

3. Now your Firefox ready t surf internet but one more issue there. Fedora may user your ADSL router or Modem as the DNS server. In other way Fedora may uses some less powerful DNS server for look-up. So  your DNS look-up will be slow and wrong most of the time. This will cause to Curl errors and slow loading errors. So we have to set some powerful DNS server for look-up purpose in Fedora. Here is the steps.

nameserver 8.8.8.8
nameserver 8.8.4.4