WordPress instance is marked as broken on CloudLinux OS: timeout: fork system call failed: Cannot allocate memory

Symptoms

• WordPress instance is marked as broken on CloudLinux OS: 
  

  CONFIG_TEXT: timeout: fork system call failed: Cannot allocate memory

• The following errors can be found in the /var/log/plesk/panel.log:
  

  CONFIG_TEXT: ERR [extension/wp-toolkit] An error occurred while executing WP-CLI command for instance: WordPress instance #504 ('http://example.com'). timeout: fork system call failed: Cannot allocate memory
  ERR [util_exec] proc_close() failed ['/usr/local/psa/admin/bin/filemng' 'johndoe' 'base64' '/var/www/vhosts/example.com/httpdocs/wp-includes/version.php'] with exit code [1]
  ERR [panel] '/usr/local/psa/admin/bin/filemng' 'johndoe' 'base64' '/var/www/vhosts/example.com/httpdocs/wp-includes/version.php' failed with code 1.
  stdout:
  filemng: Error occured during /usr/bin/base64 command: No child processes
  System error 10: No child processes

Cause

Misconfiguration in CageFS.

Resolution

1. Log into Plesk.

2. Go to Extensions > My Extensions > CageFS > Open.

3. Disable the subscription system user (and additional user if it exists) by moving it to Disabled form.

4. Enable the subscription system user back by moving it to Enabled form.