PHP Composer page fails to load for a domain in Plesk: Class "Zend_Log_Exception" not found

Symptoms

• PHP Composer page fails to load for a domain in Plesk. Either a blank page or one of the following error messages is shown in a web-browser:

  PLESK_INFO: 500 error

  ---

  PLESK_INFO: Server Error
  500 Error
  Class "Zend_Db_Adapter_Exception" not found
  Type Error
  Message Class "Zend_Db_Adapter_Exception" not found
  File Abstract.php
  Line 144

  ---

  PLESK_INFO: ERROR: Uncaught Error: Class "Zend_Log_Exception" not found in /opt/psa/admin/plib/vendor/plesk/zf1/library/Zend/Log/Writer/Stream.php:81 ...

• The following error message appears in /var/log/plesk/panel.log with debug mode enabled:

  CONFIG_TEXT: ERR [panel] Exception: PHP Warning: file_get_contents(/etc/plesk-release): Failed to open stream: Too many open files; File: ...

Cause

sw-engine Plesk service reaches the open files limit and can't load PHP Composer.

Resolution

Increase the open files limit for sw-engine:

1. Connect to the Plesk server via SSH.

2. Copy sw-engine.service unit file to /etc/systemd/system:

   # cp /usr/lib/systemd/system/sw-engine.service /etc/systemd/system/

3. Open the copied file in a text editor. In this example, we are using the vi editor:

   # vi /etc/systemd/system/sw-engine.service

4. Add the line below under the [Service] section:

   CONFIG_TEXT: LimitNOFILE=180000

5. Save the changes and close the file.

6. Restart daemon and sw-engine services:

   # systemctl daemon-reload && systemctl restart sw-engine.service