Article ID: 123662, created on Nov 24, 2014, last review on Nov 24, 2014

  • Applies to:
  • Plesk Automation 11.5


The following error during changing parameters of mailbox:

Error while creating e-mail box:
Internal error.
PHP Warning: psasem_lock() failed for semnum 15: semaphore is already acquired
Line: 41
File: /usr/local/psa/admin/plib/Semaphore.php


The PHP warning is visible in the panel as display_errors flag is set to On in the php.ini file. The sem_acquire() function in Semaphore.php is causing the warning during the successful mailbox creation, meaning that subsequent calls with the same semaphore will block indefinitely until the semaphore is released. Unfortunately, PHP does not yet support any method of querying the state of a semaphore in a non-blocking manner.


Configure the panel to not display PHP warnings:

  1. Modify the /usr/local/psa/admin/conf/php.ini file and set the flag display_errors to Off.

  2. Restart the following services:

    /etc/init.d/sw-cp-server restart
    /etc/init.d/sw-engine restart

Note, 'display_errors' with the value Off is an internal Plesk system flag that should not be changed.

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