Troubleshooting: Can’t Resolve Hostname

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You may find the “can’t resolve hostname” or “temporary failure in name resolution” error when using retrieval command like wget, cURL, ping or nslookup. There are many reasons why these commands can cause an error, including file corruption.  For the sake of brevity, we look towards commonalities between these commands to solve the issue.

These commands connect to the Internet using gateways to communicate and provide information.   If the connection from your local machine, in this case, a CentOS server, is disconnected you’ll likely run into issues trying to access the world wide web. In this troubleshooting tutorial, we’ll show you some common solutions to connectivity issues.

Step 1: Amongst many other configuration tasks, the resolv.conf file is used to resolve DNS requests. Manually editing the resolv.conf file to configure name resolution will only do so temporarily. The Network Manager controls this essential /etc/resolv.conf file to create permanent changes. So, we’ll first stop and disable the Network Manager:

Note
Be sure to run these commands as the root user, or a privileged user using sudo before each command.

chkconfig NetworkManager off; service NetworkManager stop

 

Step 2: The method for permanent changes is to edit the /etc/sysconfig/network-scripts/ifcfg-eth0 file instead of resolv.conf file. Open the file:

vim /etc/sysconfig/network-scripts/ifcfg-eth0

Next, we’ll set our DNS IP’s to use Google’s Public DNS (8.8.8.8 & 8.8.4.4).

DEVICE="em1"
BOOTPROTO="static"
DNS1="127.0.0.1"

DNS2="8.8.8.8"


DNS3="8.8.4.4"

GATEWAY="some_ip"
HWADDR="hwid"
IPADDR="some_ip"
IPV6INIT="yes"
NETMASK="255.255.255.0"
NM_CONTROLLED="yes"
ONBOOT="yes"
TYPE="Ethernet"

Save and quit the file using ESC and :wq.

 

Step 3: Enable and restart your network, using the commands associated with your server version.

CentOS 6, CloudLinux 6, RHEL 6:

chkconfig network on

service network start

 

CentOS 7, CloudLinux 7, RHEL 7:

systemctl enable network.service

systemctl start network.service

 

Step 4: Test the reachability of a host by using ping, curl, wget or any testing tool of your choice. In our example, we’ve successfully ping’d Google!  

ping google.com
PING google.com (172.217.4.46) 56(84) bytes of data.
64 bytes from lga15s46-in-f14.1e100.net (172.217.4.46): icmp_seq=1 ttl=57 time=6.65 ms
64 bytes from lga15s46-in-f14.1e100.net (172.217.4.46): icmp_seq=2 ttl=57 time=6.68 ms
64 bytes from lga15s46-in-f14.1e100.net (172.217.4.46): icmp_seq=3 ttl=57 time=6.68 ms

You don’t have to rack your brain over connectivity issues!  Liquid Web customers enjoy 24/7 support for our VPS Managed products. Our knowledgeable team of support techs have experience with solving errors of this nature.  Access our support team through a ticket, chat or phone call!

Resolvers and Resolv.conf

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Resolvers are a form of DNS server that usually exist on a local network (such as the one your ISP operates to connect you to the internet) and handle all DNS requests from the computers that using the network.

For example, when you type a domain name into your web browser your computer contacts your ISP’s local resolvers and asks for the domain name. The local resolver then does the DNS work, turning the name into an IP address. Your computer then connects to the server at the IP address and requests the web page.

Continue reading “Resolvers and Resolv.conf”