gethostbyname

(PHP 4, PHP 5, PHP 7, PHP 8)

gethostbyname 返回主机名对应的 IPv4地址。

说明

gethostbyname ( string $hostname ) : string

返回主机名 hostname 对应的 IPv4 互联网地址。

参数

hostname

主机名

返回值

成功时返回 IPv4 地址,失败时原封不动返回 hostname 字符串。

范例

Example #1 简单的 gethostbyname() 例子

<?php
$ip 
gethostbyname('www.example.com');

echo 
$ip;
?>

参见

  • gethostbyaddr() - 获取指定的IP地址对应的主机名
  • gethostbynamel() - 获取互联网主机名对应的 IPv4 地址列表
  • inet_pton() - Converts a human readable IP address to its packed in_addr representation
  • inet_ntop() - Converts a packed internet address to a human readable representation

User Contributed Notes

gabriel at nexcore dot com dot br 10-Aug-2016 09:43
For the "dig" solution, here is a better one:

<?php
  $IP
= `/usr/bin/dig $host. A +short | /usr/bin/tail -n1`
?>

Using tail because dig, even in the +short form, may return CNAME entries first, and also may return many, many entries (see "dig google.com").

Usig the dot at the end of the host to not perform domain searches.

This works also when $host = IP address already

Will return empty string in case o resolve failure (invalid hostname)
Dennis B. 15-Feb-2016 12:33
Options for the underlying resolver functions can be supplied by using the RES_OPTIONS environmental variable. (at least under Linux, see man resolv.conf)

Set timeout and retries to 1 to have a maximum execution time of 1 second for the DNS lookup:
<?php
  putenv
('RES_OPTIONS=retrans:1 retry:1 timeout:1 attempts:1');
 
gethostbyname($something);
?>

You should also use fully qualified domain names ending in a dot. This prevents the resolver from walking though all search domains and retrying the domain with the search domain appended.
php at nemon dot be 17-Aug-2015 04:14
Always add the root . at the end or your server can add it's own suffix.
example: abc.com could become abc.com.yourcompany.com if you don't use abc.com.

I also find this function a litle bit limited because it doesn't tell you if the resolve failed.

TO adress all those issues I use :

function host2ip($host)
{
    $host=trim($host.'.'); // clean and add root .
    $ip= gethostbyname($host);
    if($ip==$host) $ip='';// empty IP if there is no ip
    return $ip;
}
devers 11-Dec-2014 05:37
This function says "Returns the IPv4 address or a string containing the unmodified hostname on failure.

This isn't entirely true, any hostname with a null byte in it will only return the characters BEFORE the null byte.

<?php
$hostname
= "foo\0bar";
var_dump($hostname );
var_dump(gethostbyname($hostname ));
?>

Results:
string 'foo?bar' (length=7)
string 'foo' (length=3)
Ome Ko 16-Mar-2013 08:34
If you do a gethostbyname() and there is no trailing dot after a domainname that does not resolve, this domainname will ultimately be appended to the server-FQDN by nslookup.

So if you do a lookup for nonexistentdomainname.be your server may return the ip for nonexistentdomainname.be.yourhostname.com, which is the server-ip.

To avoid this behaviour, just add a trailing dot to the domainname; i.e. gethostbyname('nonexistentdomainname.be.')
Emmett Brosnan 01-Feb-2012 11:09
Grabbing IPs for multiple hosts:

<?php
function getAddrByHost($hosts, $timeout = 3) {
 
$returnString = '';
  foreach (
$hosts as $host) {
   
$query = `nslookup -timeout=$timeout -retry=1 $host`;
    if (
preg_match('/\nAddress: (.*)\n/', $query, $matches))
     
$returnString .= trim($matches[1]) . '<br>';
   
$returnString .= $host . '<br>';
  }
  return
$returnString;

}

$hostArray[] = 'www.domain1.com';
$hostArray[] = 'www.domain2.com';
//$hostArray[] = 'www.domain3.com';
//$hostArray[] = 'www.domain4.com';

$returnString = getAddrByHost($hostArray);
echo
$returnString;
?>
Alexandre (d) 17-Jul-2011 09:28
Important note: You should avoid its use in production.

DNS Resolution may take from 0.5 to 4 seconds, and during this time your script is NOT being executed.

Your customers may think that the server is slow, but actually it is just waiting for the DNS resolution response.

You can use it, but if you want performance, you should avoid it, or schedule it to some CRON script...
nirazuelos at gmail dot com 12-Aug-2009 08:52
This is the best method I've come up with to resolve any host-name to ip-address, it's quick and reliable and has support for timeout! An invalid address, a unicode string for exmaple, returns after 4~ seconds, instead of 8~ with gethostbyname! It works only with unix though.

<?php
function getAddrByHost($host, $timeout = 3) {
  
$query = `nslookup -timeout=$timeout -retry=1 $host`;
   if(
preg_match('/\nAddress: (.*)\n/', $query, $matches))
      return
trim($matches[1]);
   return
$host;
}
?>
manalejandro at gmail dot com 24-May-2008 08:59
This logic solution to problem checking dns reverse name resolution:

<?php
$ip
= gethostbyname($host);
if(
ip2long($ip) == -1 || ($ip == gethostbyaddr($ip) && preg_match("/.*\.[a-zA-Z]{2,3}$/",$host) == 0) ) {
    echo
'Error, incorrect host or ip';
    }
else {
    echo
'Ok';
}
?>
geoff at spacevs dot com 05-Dec-2007 07:37
I put this in a prepend script for all my websites to cut down the amount of abuse by automated scripts.
<?PHP
        $blacklists
= array('web.sorbs.net');
       
$parts  = explode('.', $_SERVER['REMOTE_ADDR']);
       
$ip     = implode('.', array_reverse($parts)) . '.';
        foreach(
$blacklists as $bl) {
               
$check = $ip . $bl;
                if (
$check != gethostbyname($check)) {
                               
error_log('PHP Security: [DNSBL] - ' . $_SERVER['REMOTE_ADDR'] . ' - ' . $bl);
                                die(
'Put a detailed error here so the client knows why they have been blocked');
                }
        }
?>
Florian Holzhauer 12-Sep-2007 03:02
If name resolution fails with apache2, mod_chroot and php5, add
LoadFile /lib/libnss_dns.so.2
to the mod_chroot config.
guwapo at thedoghouse dot bz 07-Sep-2007 08:25
referring to ralphbolton at mail2sexy dot com comment:

(at least in 5.2.0 + djbdns-dnscache) gethostbyname does not really seem to cache entries. If somebody notices a speed-up after the second lookup of the same domain - that's most likely your dns-cache itself, not some php-internal dns-cache.

It does cache the entries in your /etc/resolv.conf (e.g. what dns to use) so I agree with him, that stopping and starting apache, will reload the resolv.conf.
von at student dot chalmers dot se 20-Jul-2007 03:50
When using PHP and Apache in a chroot environment on RedHat Linux, I have found that I need to bind-mount /var/run/nscd to get this to work. Apparently, the socket in that directory is needed for all the DNS things.
Josh Finlay josh at glamourcastle dot com 04-Nov-2006 06:55
gethostbyname and gethostbynamel does not ask for AAAA records. I have written two functions to implement this. gethostbyname6 and gethostbynamel6. I don't believe this issue has been addressed yet.

They are made to replace gethostbyname[l], in a way that if $try_a is true, if it fails to get AAAA records it will fall back on trying to get A records.

Feel free to correct any errors, I realise that it is asking for *both* A and AAAA records, so this means two DNS calls.. probably would be more efficient if it checked $try_a before making the query, but this works for me so I'll leave that up to someone else to implement in their own work.. the tip is out there now anyway..

Here is the code:

    function gethostbyname6($host, $try_a = false) {
        // get AAAA record for $host
        // if $try_a is true, if AAAA fails, it tries for A
        // the first match found is returned
        // otherwise returns false

        $dns = gethostbynamel6($host, $try_a);
        if ($dns == false) { return false; }
        else { return $dns[0]; }
    }

    function gethostbynamel6($host, $try_a = false) {
        // get AAAA records for $host,
        // if $try_a is true, if AAAA fails, it tries for A
        // results are returned in an array of ips found matching type
        // otherwise returns false

        $dns6 = dns_get_record($host, DNS_AAAA);
        if ($try_a == true) {
            $dns4 = dns_get_record($host, DNS_A);
            $dns = array_merge($dns4, $dns6);
        }
        else { $dns = $dns6; }
        $ip6 = array();
        $ip4 = array();
        foreach ($dns as $record) {
            if ($record["type"] == "A") {
                $ip4[] = $record["ip"];
            }
            if ($record["type"] == "AAAA") {
                $ip6[] = $record["ipv6"];
            }
        }
        if (count($ip6) < 1) {
            if ($try_a == true) {
                if (count($ip4) < 1) {
                    return false;
                }
                else {
                    return $ip4;
                }
            }
            else {
                return false;
            }
        }
        else {
            return $ip6;
        }
    }
chris at chollis dot net 15-Oct-2006 10:57
mmucklo raises a valid point, however the function to use would be getmxrr() in the simplest case, or alternatively checkdnsrr() if you so wish; getdnsrr() does not exist.

On another note, it can be a pain (when iterating with while loops for example) that on failure gethostbyname() returns the hostname, rather than FALSE. You could wrap it in a simple user function, to "correct" this:

<?php

function fixed_gethostbyname ($host) {
   
// Try the lookup as normal...
   
$ip = gethostbyname($host);
   
// ...but if it fails, FALSE is returned instead of the unresolved host
   
if ($ip != $host) { return $ip; } else return false;
}

?>
Peter <toomuchphp-phpman at yahoo dot com> 05-Sep-2006 06:33
One way to discover your IP address automatically:

<?php

// need to trim() because whitespace will confuse the name lookup
$myIP = gethostbyname(trim(`hostname`));
echo
$myIP;

?>
mmucklo at yahoo dot com 16-Aug-2006 11:05
One note about using gethostbyname() for checking email address domains:

If the name doesn't resolve, follow up with getdnsrr() and make sure they don't have an MX entry before returning an error.

It is possible for a domain name not to have an A record, but still have an MX entry.
Marc M 08-Aug-2006 08:33
Just a heads up. I was using this function on my site to verify email host addresses. I thought all was good, until a potential client contacted me and said they couldn't sign up correctly. They have a valid email address and domain, but this function failed.

Good luck.
ralphbolton at mail2sexy dot com 06-Apr-2006 01:10
On a side-note, PHP (5.0.4, but probably other versions too) can cache gethostbyname information.

In short, once PHP looks up an address, it may not actually perform another lookup as you may expect. In my particular case (I think) the problem was a change to resolv.conf didn't take effect inside PHP (although nslookup/ping etc worked fine). Stop/Starting Apache fixed it (although a simple 'restart' (kill -HUP) didn't).

In short, if you change resolv.conf, stop and restart Apache.
ivan[DOT]pirog[AT]gmail[DOT]com 14-Mar-2006 06:57
Function returns boolean:
<?php
function isDomainResolves($domain)
{
     return
gethostbyname($domain) != $domain;
}
?>
mcgrof at gmail dot com 21-Oct-2005 09:10
Better yet:
<?php
$ip
= rtrim(`/usr/bin/dig $host A +short`);
?>
mcgrof at gmail dot com 21-Oct-2005 09:05
In PHP4 you can use gethostbyname() but I have found this unreliable when doing lookups on entries that return A records on the private network. PHP5 has a much better routine -- dns_get_record(). If you are stuck with PHP4 or don't want to upgrade you can use dig:

<?php
$ip
= `/usr/bin/dig $host A +short`;
?>
tabascopete78 at yahoo dot com 18-Aug-2005 12:29
I was using file_get_contents on a set of URLs. Some of them URLs were invalid (the structure of it was ok but the DNS hosts couldn't resolve them) and I kept getting an annoying warning. I wanted to check the DNS somehow but existing check dns function in php doesn't have one for windows and the one a person supplied there does not work 100% of the time.

Instead use this function to try to resolve a host. This won't throw any warnings, you just need to check the output. You'll get the same warnings with fopen and fsockopen.
cox at idecnet dot com 26-Dec-2004 12:15
For doing basic RBL (Real Time Blacklist) lookups with this function do:

<?php
$host
= '64.53.200.156';
$rbl  = 'sbl-xbl.spamhaus.org';
// valid query format is: 156.200.53.64.sbl-xbl.spamhaus.org
$rev = array_reverse(explode('.', $host));
$lookup = implode('.', $rev) . '.' . $rbl;
if (
$lookup != gethostbyname($lookup)) {
    echo
"ip: $host is listed in $rbl\n";
} else {
    echo
"ip: $host NOT listed in $rbl\n";
}
?>

Tomas V.V.Cox
Vincent 14-Jul-2004 09:14
Note that if you pass an IP address to gethostbyname() it will return that IP address.
30-Mar-2004 02:49
The dns entries get cached, whether they exist or not.  Expect really good response times after the first one.
christian at SPAM at IS at DEAD at MEAT at karg dot org 01-Apr-2003 04:12
I had difficulty getting gethostbyname to work under OpenBSD 3.2 and Apache, until I discovered that the default Apache chroot caused the problem.

To get PHP's gethostbyname to work, you need resolv.conf (and possibly hosts) in /var/www/etc (assuming default install dirs).
tonyhana at sixzeros dot com 04-Jul-2002 07:43
<?php
//script to time DNS propagation
//(Above script modified slightly to show micro time)
//seems pretty damn quick to me.. I'm getting .0055 sec worstcase badhost times.

//A known good dns name (my own)
   
$nametotest = "fuzzygroup.com";
   
//Call address test function
   
$time_start = getmicrotime();
   
testipaddress($nametotest);
   
$time_end = getmicrotime();
   
$time = $time_end - $time_start;
    echo
"Good Host Search took $time seconds<br><br>";

//A known bad name (trust me)
   
$nametotest = "providence.mascot.com";
   
$time_start = getmicrotime();
   
testipaddress($nametotest);
   
$time_end = getmicrotime();
   
$time = $time_end - $time_start;
    echo
"Bad Host Search took $time seconds<br>";
   
   
function
getmicrotime(){
    list(
$usec, $sec) = explode(" ",microtime());
    return ((float)
$usec + (float)$sec);
    }

//ip address checking function
//for real use should have a return value but example code
function testipaddress ($nametotest) {
   
$ipaddress = $nametotest;
   
$ipaddress = gethostbyname($nametotest);
    if (
$ipaddress == $nametotest) {
        echo
"No ip address for host<br>";
    }
    else {
        echo
"good hostname, $nametotest ipaddress = $ipaddress<br>";
    }
}

//Recommended fix for sql applications:
// store url to temporary table
// run second process periodically to
// check urls and update main table
?>
sjohnson at fuzzygroup dot com 16-Mar-2002 10:27
<?php

//script to see if host exists on Internet

//following up on the above point about host name
//checking and SQL timeouts, run this test script
//and see how long it takes for 2nd call to
//hostname check to fail
//NOTE -- not PHP's fault -- nature of DNS

//A known good dns name (my own)
   
$nametotest = "fuzzygroup.com";
   
//Call address test function
   
testipaddress($nametotest);

//A known bad name (trust me)
   
$nametotest = "providence.mascot.com";
//Call address test function
   
testipaddress($nametotest);
   
//ip address checking function
//for real use should have a return value but example code
function testipaddress ($nametotest) {
   
$ipaddress = $nametotest;
   
$ipaddress = gethostbyname($nametotest);
    if (
$ipaddress == $nametotest) {
        echo
"No ip address for host, so host "
            
. "not currently available in DNS and "
            
. "probably offline for some time<BR>";
    }
    else {
        echo
"good hostname, ipaddress = $ipaddress<BR>";
    }
}

//Recommended fix for sql applications:
// store url to temporary table
// run second process periodically to
// check urls and update main table
?>