Fatal error settings.php on line 221

What version of PHP are you on?

5.3

filter_var is a PHP function available in version 5.2+
https://php.net/manual/en/function.filter-var.php

I cannot imagine a reason why that would fail but I will consider removing it.

Who’s your web host? Would you mind asking them if they have any idea why that native PHP function would not work on their server?

nic.ru

They advertise PHP 5.1 to 5.6 here:
https://www.nic.ru/dns/service/hosting/index.html#answer5

So we need a definite confirmation that your server is running at least PHP 5.2, the minimum version required by WordPress.

phpinfo():

PHP Version 5.3.29

System 	Linux alfpl.nichost.ru 4.4.0-77-generic #98-Ubuntu SMP Wed Apr 26 08:34:02 UTC 2017 x86_64
Build Date 	Sep 28 2016 18:37:56
Configure Command 	'./configure' '--with-layout=GNU' '--prefix=/usr/local/php53' '--sysconfdir=/etc/php/5.3' '--with-config-file-path=/etc/php/5.3' '--with-config-file-scan-dir=/etc/php/5.3/conf.d' '--enable-libxml' '--enable-mysqlnd' '--with-apxs2=/usr/bin/apxs' '--with-zlib-dir=/usr' '--disable-all'
Server API 	Apache 2.0 Handler
Virtual Directory Support 	disabled
Configuration File (php.ini) Path 	/etc/php/5.3
Loaded Configuration File 	/etc/php/5.3/php.ini
Scan this dir for additional .ini files 	/etc/php/5.3/conf.d
Additional .ini files parsed 	(none)
PHP API 	20090626
PHP Extension 	20090626
Zend Extension 	220090626
Zend Extension Build 	API220090626,NTS
PHP Extension Build 	API20090626,NTS
Debug Build 	no
Thread Safety 	disabled
Zend Memory Manager 	enabled
Zend Multibyte Support 	disabled
IPv6 Support 	enabled
Registered PHP Streams 	compress.zlib, php, file, glob, data, http, ftp, https, ftps, zip
Registered Stream Socket Transports 	tcp, udp, unix, udg, ssl, sslv3, tls
Registered Stream Filters 	zlib.*, string.rot13, string.toupper, string.tolower, string.strip_tags, convert.*, consumed, dechunk, convert.iconv.*
...
 

PhpInfo

Thank you all, the answer came from hosting support:

In this case, you need to connect the PHP filter extension.
You can connect the extension through the hosting control panel:
– log in to the control panel (https://hosting.nic.ru), using your contract number and password;
– go to the section “Web server” – “Manage modules”;
– Click on the link “PHP (configure the module);
– in the “PHP module extensions” block, click the “Manage extensions” link;
– Select the checkbox “Show all extensions”;
– Find the desired extension in the list that opens, check its box and save the changes.

I’m glad you got it working. I wasn’t aware that could be disabled. Thanks for sharing the solution.