Domain Name System (DNS) is a service that provides the resolution of host names to IP addresses. Use the [tag:dns] tag when you are troubleshooting DNS issues, configuring a DNS resolver or server, or are trying to understand DNS's involvement in your situation.

learn more… | top users | synonyms

148
votes
17answers
205k views

How can I resolve a hostname to an IP address in a Bash script?

What's the most concise way to resolve a hostname to an IP address in a Bash script? I'm using Arch Linux.
100
votes
13answers
312k views

How do I set my DNS when resolv.conf is being overwritten?

Most of the info I see online says to edit /etc/resolv.conf, but any changes I make there just get overridden. $ cat /etc/resolv.conf # Dynamic resolv.conf(5) file for glibc resolver(3) generated by ...
56
votes
8answers
108k views

What DNS servers am I using?

How can I check which DNS server am I using (in Linux)? I am using network manager and a wired connection to my university's LAN. (I am trying to find out why my domain doesn't get resolved)
51
votes
5answers
44k views

What is the point of sshd “UseDNS” option?

I know what it does, but i don't know why. What attack(s) does it prevent ? Is it relevant for all kind of authentication methods ? (hostbased, password, publickey, keyboard-interactive ...)
26
votes
7answers
16k views

Can I create override dns similar to writing in /etc/hosts without root access

I want to set a dns record that my browser will use, but I don't have root access, so I can't modify /etc/hosts. I need to do this for testing vhosts with apache, whose dns hasn't yet been set up. I ...
19
votes
4answers
36k views

How to clear DNS cache on DD-WRT

How can I clear the DNS cache in DD-WRT on my router? DD-WRT uses the dnsmasq daemon.
15
votes
2answers
20k views

What is a “recursive DNS query”? [closed]

Can someone explain in short what "recursive DNS query" means and how it can be considered bad?
15
votes
2answers
12k views

dig vs nslookup

Why do the commands dig and nslookup sometimes print different results? ~$ dig facebook.com ; <<>> DiG 9.9.2-P1 <<>> facebook.com ;; global options: +cmd ;; Got answer: ;; ...
15
votes
4answers
18k views

Iptables to redirect DNS lookup IP and Port

I have discovered that my ISP (verizon) is intercepting all DNS traffic on port 53. Using iptables, I want to redirect all DNS lookup traffic to a specific IP and Port (5353). Any attempt for my ...
14
votes
4answers
7k views

How do I generate SSHFP records?

I need to setup SSHFP records in the DNS for my host. I have done some searching but I haven't found any good example. What are SSHFP records? What does SSHFP records look like? How do I create ...
14
votes
2answers
16k views

Is there a way to get the Public DNS address of an instance?

I have a project wherein I need to update configuration files each time an EC2 instance is booted with the Public DNS address of the current instance. I'll be using Perl or Sed for this, so that's ...
13
votes
6answers
5k views

Host lookup that respects /etc/hosts

Utilities like host and dig let you see the IP address corresponding to the host name. There is also the getent utility that can be used to query /etc/hosts or other NSS databases. I am looking for ...
11
votes
3answers
946 views

Two commands, one pipeline

I need these two commands to be one (so I can pipe them further): dig +nottlid -t any bix.hu | egrep -v "^;;|^;|^$" | sort dig +nottlid -t any www.bix.hu | egrep -v "^;;|^;|^$" | sort I mean I ...
11
votes
4answers
12k views

How to log all my DNS queries?

How can I create logs of every DNS query that my computer makes along with the responses it gets?
11
votes
1answer
8k views

How can I override the /etc/hosts file at user level? [duplicate]

Possible Duplicate: Can I create a user-specific hosts file to complement /etc/hosts? In short: I would like to know if it is possible to get a ~/hosts file that could override the ...
11
votes
3answers
30k views

How to read the local DNS cache contents?

I know that on Windows I can issue ipconfig /displaydns and I see the local DNS's cache content. How can I list the DNS's cache content in Linux? I would like to get as much as cross-distro solution ...
10
votes
3answers
3k views

Configuring ssh fingerprints on dns to replace known_hosts fails

The SSHFP records were generated on the ssh server as follows and then added to the zone in bind: $ ssh-keygen -r www.test.us. www.test.us. IN SSHFP 1 1 ad04dfaf343a93beeb939eed1612168f7eadbed7 ...
9
votes
2answers
15k views

apache won't restart after adding VirtualHost conf file, why not?

In a CentOS 7 server, I get the following error when I type sudo apachectl restart after I add an include file at the bottom of httpd.conf: Job for httpd.service failed. See 'systemctl status ...
9
votes
5answers
26k views

How to set DNS resolver in Fedora using network-manager?

I want to try out Google public DNS. For this I need to change the nameserver address. I know it's in the file /etc/resolv.conf, but whenever I start network-manager, it overwrites the values in that ...
9
votes
1answer
215 views

Can a domain be configured to only have secondary DNS nameserver records?

I'm asking if someone can verify if my DNS hosting idea is possible or has any flaws. We would host our own primary DNS server for all zones and configure it to allow zone transfers to a set of IPs ...
9
votes
1answer
9k views

How to let `named` (bind9) forward certain domains to a different nameserver?

In dnsmasq, it's possible to forward domains to different nameservers. How can I do that in named? server=/foo.com/10.0.10.1 server=/vpn.foo.com/8.8.8.8
8
votes
5answers
24k views

DNS queries not using nscd for caching

I'm trying to use nscd (Nameservices Cache Daemon) to cache DNS locally so I can stop using Bind to do it. I've gotten it started and ntpd seems to attempt to use it. But everything else for hosts ...
8
votes
2answers
2k views

DNS lookups sometimes take 5 seconds

I have a VM running Debian Wheezy on which some hostname lookups take several seconds to complete, even though the resolver replies immediately. Strangely, lookups with getaddrinfo() are affected, ...
8
votes
2answers
11k views

curl --resolve appears to do nothing

The --help output for curl lists a --resolve option, which states --resolve <host:port:address> Force resolve of HOST:PORT to ADDRESS I'm not having any luck getting it to work though. The ...
8
votes
1answer
3k views

delay to get password prompt when ssh'ing to a public server

i have a server (debian 7) setup in my university with public ip. when I ssh into the system (from outside the campus), I get a weird delay of 5-10 seconds before I get the password prompt. Why is ...
8
votes
2answers
3k views

How to test /etc/hosts

What's the best way to confirm that your /etc/hosts file is mapping a hostname to the correct IP address? Using a tool like dig queries an external DNS directly, bypassing the hosts file.
8
votes
4answers
20k views

Reverse DNS lookups slowing down network operations on LAN

Environment My LAN setup is quite basic: A router connected to the ISP's modem and the internet My development pc directly connected to the router The router provides DHCP but does not run its ...
8
votes
1answer
1k views

First sudo always slow

The first sudo I enter on my Ubuntu 14.04 server is always slow. The password prompt displays immediately, but after I press enter it takes about 10-15 seconds until the output is printed. All sudo ...
7
votes
2answers
5k views

How does DNS name resolution work, in principle?

Right now I'm taking an online course for Linux sysadmin and I was asked a question I just generally don't understand. I know how to search for a name server, if I'm correct at least it's using the ...
7
votes
2answers
17k views

Why dig reports the dns server as 127.0.0.1 when I'm using a external DNS?

I use unbound and usually use openDNS as my DNS server. When I run dig google.com say I get SERVER: 127.0.0.1#53(127.0.0.1). What exactly is this thing listening on port #53? is this unbound or is it ...
7
votes
1answer
10k views

“Fake” DNS for a single host

I am running a bind9 dns server at my home network, serving for all my internal servers in my domain local / 192.168.x.x - one of those, extweb.local 192.168.1.33 is also visible from the internet as ...
7
votes
3answers
102k views

How to flush local DNS cache in CentOS

(I am aware that googling this question gives me tons of stuff, but literally none worked) I'm looking for a way to flush the local DNS cache on a Centos 6 system, it is not running any DNS server or ...
7
votes
4answers
45k views

Why can't I ping Google?

I can't ping google.com (unknown host). But I can ping IP addresses. I tried to ping the IP address of Google but it doesn't work. resolv.conf nameserver 8.8.8.8 nameserver 209.139.209.33 ...
7
votes
1answer
2k views

Why is dnsmasq putting my router IP in /etc/resolv.conf instead of 127.0.0.1?

I'm having DNS resolution issues in various contexts which appear to trace back to my networking configuration. I'm running just the dnsmasq-base installation of dnsmasq on two Linux installations ...
7
votes
2answers
656 views

Firefox unable to access domains defined in /etc/hosts if Network Manager is disconnected from a network

For developing web sites, I define test domains in /etc/hosts : 127.0.0.1 example.org I can then access example.org in the browsers. However I when the Network Manager is not connected to any ...
6
votes
5answers
8k views

/etc/resolv.conf changes during reboot

My ISP asked me to use custom nameserver settings. I have placed these in /etc/resolv.conf. Unfortunately, every time I reboot the computer, the contents of this file is changed. To connect to the ...
6
votes
5answers
33k views

Name resolution doesn't work, but nslookup does

I am having a very strange problem with my installation of Solaris 11. DNS resolution just won't work, but strangely enough, nslookup does and connectivity is fine: root@solarisxyz:~# ping ...
6
votes
1answer
509 views

Why the difference between network addresses reported by hostname and ping?

I have tried hostname and ping in a cluster machine, with different outputs. I am wondering what is the difference between the two? For example, on the same machine, hostname outputs node4.XXX and ...
6
votes
2answers
12k views

How to get networkmanager to configure domain specific name servers with openresolv + dnsmasq

I often connect to multiple network simultaneously. Each of these networks provide nameserver configuration via dhcp. E.g. Network 1: (eth0): domain company1.corp # nameserver 192.168.0.253 ...
6
votes
2answers
3k views

DNS resolution problem with Fedora 20

I have a newly built Fedora 20 server that I've just hooked to my network. It's a virtual server running on a VirtualBox host. Everything seems to be working but I have a problem with name resolution. ...
6
votes
1answer
10k views

How to check if port forwarding is enabled?

I have just set up a DNS server for my own network, and many guides online suggest to make sure that port forwarding on port 53 is not enabled. The thing that is not clear to me is this: should I ...
6
votes
2answers
6k views

Blocking Websites with /etc/hosts

There's a website, www.example.com, that I tried to block myself from accessing because it wastes too much of my time. So I configured my /etc/hosts file. I added the following lines, to block the ...
6
votes
1answer
10k views

Debian cannot resolve hostnames

I have a problem resolving host names on Debian running on vmware. It just stopped working out of the blue. Somewhere after uninstalling percona server and deleting /etc/mysql . Initially it thought ...
6
votes
1answer
3k views

resolve the server hostname of a dnsmasq server with multiple subnets

I have a self-made Linux router running dnsmasq. It has two different NICs through which clients are connected; one of them has the subnet 192.168.1. and one the subnet 192.168.2.. My ...
6
votes
2answers
10k views

Using DNSMasq for Local Hostname Resolution

I'm working on setting up a home intranet for me and my roommates. My idea is that we'll be able to store things like past utility bills in a place that's more accessible than a drawer in the kitchen ...
5
votes
5answers
7k views

How to overcome libc resolver limitation of maximum 3 nameservers?

Suppose I work in environment with number of domain changes and slow propagation. I want to test domain configuration immediately after setting change but the propagation is slow. So I want to add ...
5
votes
2answers
144 views

Should /etc/hosts contain the domain name or the FQDN?

If I want to add an entry to /etc/hosts to resolve all traffic for example.com to 1.2.3.4, do I need to add 1.2.3.4 example.com 1.2.3.4 www.example.com 1.2.3.4 smtp.example.com 1.2.3.4 ...
5
votes
3answers
15k views

How to create a custom dynamic DNS solution?

You all probably know commercial dynamic DNS providers like dyndns.org or no-ip.com. But how to create a similar service for just a handful of machines? What server software would be best suited for ...
5
votes
1answer
2k views

Why is my computer trying to send ICMP type 3 to OpenDNS?

In my firewall logs I see lots of entries like this. IN= OUT=eth0 SRC=192.168.1.105 DST=208.67.220.220 LEN=148 TOS=0x00 PREC=0xC0 TTL=64 ID=55705 PROTO=ICMP TYPE=3 CODE=3 [SRC=208.67.220.220 ...
5
votes
3answers
4k views

DNS Master vs Slave and Primary vs Secondary

I'm a little confused about the difference between a "secondary name server" and a "slave name server" and a "primary name server" and a "master name server"   I understand that a slave name server ...