Example Uses of the Linux Host Command

Obtain IP address or hostname information from a Linux shell prompt

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By
Gary Newell
Writer
Gary Newell was a freelance contributor, application developer, and software tester with 20+ years in IT, working on Linux, UNIX, and Windows.
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Gary Newell
Updated December 09, 2019

The Linux host command finds the IP address for a domain and vice versa.

The Host Command

On its own, the host command returns a list of all the possible switches that can be used with it.

To get the list type the following into a terminal window:

host

The following results will be displayed:

  • -a is equivalent to -v -t ANY.
  • -c specifies query class for non-IN data.
  • -C compares SOA records on authoritative nameservers.
  • -d is equivalent to -v.
  • -l lists all hosts in a domain, using AXFR.
  • -i performs IP6.INT reverse lookup.
  • -N changes the number of dots allowed before root lookup is done.
  • -r disables recursive processing.
  • -R specifies number of retries for UDP packets.
  • -s stipulates that a SERVFAIL response should stop query.
  • -t specifies the query type.
  • -T enables TCP/IP mode.
  • -v enables verbose output.
  • -w specifies to wait forever for a reply.
  • -W specifies how long to wait for a reply.
  • -4 uses IPv4 query transport only.
  • -6 uses IPv6 query transport only.
  • -m sets the memory debugging flag.
  • -V prints version number and exits.

Get the IP Address for a Domain Name

host command

To return the IP address for a domain name, simply type the following command:

host <domainname>

For example, to find the domain name for linux.lifewire.com, type the following command.

host linux.lifewire.com

The results from the host command will be as follows:

linux.lifewire.com is an alias for dynglbcs.lifewire.com.dynglbcs.lifewire.com has address 207.241.148.82

Of course, linux.lifewire.com is a subdomain for lifewire.com. Running the host command against the full lifewire.com domain name returns a different IP address.

lifewire.com has address 207.241.148.80

There is some further output from the host command against lifewire.com, as it displays how mail is handled.

For example:

lifewire.com mail is handled by 500 ALT4.ASPMX.L.Google.com

Be careful about investing too much in these results. Eagle eyes surely note the discrepancy between the text of this article and the screenshot in this section. The latter was taken several months after the former had been previously reviewed. In that time, Lifewire's servers migrated to a content delivery network such that the IP addresses appear to have changed when, in fact, merely the mechanism of content delivery changed (for the better).

Get the Domain Name From an IP Address

The opposite of returning the IP address from a domain name is returning the domain name from an IP address.

You can do this by typing the following into a terminal window:

host <IP Address>

For example, we know that 207.241.148.80 is the IP address for Lifewire.com. Type the following into a terminal window:

host 207.241.148.80

The results are as follows:

82.148.241.207.in-addr.arpa domain name pointer glbny.lifewire.com.

The host command by default returns just enough information but you can get a more detailed output by using either the -d or -v switch as follows:

host -d linux.lifewire.com

The results from the above command show the domain that was looked up along with any results. It also returns the SOA details for a domain.

Return the SOA Details for a Domain

SOA stands for Start of Authority. If you register a domain name and then host that domain with a web hosting company, the web hosting company must maintain an SOA for that domain. It provides a way of keeping track of domain names.

You can find the SOA details for a domain by typing the following command:

host -C <ipaddress>
host -C <domainname>

For example, type the following into a terminal window:

host -C lifewire.com

There are a number of results returned but they all contain the same fields which are as follows:

  • The primary name server
  • The responsible party for the domain
  • A timestamp which changes when the domain is updated
  • The number of seconds before the zone should be refreshed
  • The number of seconds before a failed refresh should be retried
  • The upper limit in seconds before a zone is no longer considered authoritative
  • The negative result TTL

Summary

There are obviously many other switches, such as -l, which provides a listing, and -T, which searches using TCP/IP instead of UDP.

You will find that a lot of web servers will refuse these types of queries.

In general, you will probably only need to use the host command to return either the IP address for a domain name or the domain name for an IP address.