Error while opening PHP file: PHP Warning: require_once(PEAR/Info.php)

Symptoms

Cannot open a PHP file which uses PEAR library, the following error appears:

CONFIG_TEXT: Internal Server error 500

The following error is found in /var/www/vhosts/example.com/logs/error_log

CONFIG_TEXT: [fcgid:warn] [pid 20442:tid 140600493983488] [client 203.0.113.2:60260] mod_fcgid: stderr: PHP Fatal error: require_once(): Failed opening required 'PEAR/Info.php' (include_path='.:/usr/share/pear:/usr/share/php') in /var/www/vhosts/example.com/httpdocs/pear.php on line 2
[fcgid:warn] [pid 20442:tid 140600485590784] [client 203.0.113.2:60262] mod_fcgid: stderr: PHP Warning: require_once(PEAR/Info.php): failed to open stream: No such file or directory in /var/www/vhosts/example.com/httpdocs/pear.php on line 2

Cause

PEAR module is missing from the system. 

Resolution

1. Login to the server over SSH

2. Determine the PEAR package name:

# pear search info
WARNING: channel "pear.php.net" has updated its protocols, use "pear channel-update pear.php.net" to update
Retrieving data...0%
..Matched packages, channel pear.php.net:
=======================================
Package Stable/(Latest) Local
File_Infopath 0.1.0 (alpha) A package to read the schema and views in html from a Microsoft Infopath file
PEAR_Info 1.9.2 (stable) Show Information about your PEAR install and its packages
PHP_CompatInfo 1.9.0 (stable) Find out the minimum version and the extensions required for a piece of code to run

3. Install the PEAR library:

# pear install --alldeps PEAR_Info

4. Set the PEAR path for the domain according to recommendations in article: How to enable PEAR support for the domain?