The interactive command:
is used when due to problems during startup or program crashes, the buffering resources become locked. For example, a program may lock the resources to add event data to the buffers and then crash before it unlocks the resources. Other programs and the buffering process are then prevented from accessing these resources.
To recover cleanly, these processes should be stopped, bufutil run with the -u command (unlock), and then the buffer server and other API processes restarted. Under UNIX this would typically be accomplished by running the pistop script followed by the pistart script. The pistart script uses this command when it starts to ensure that it can cleanly start the buffering process.
Under certain error conditions, or if different users start different PI-API programs on a UNIX system, it may be necessary to become root before running bufutil-u to succeed in removing the resources. Typically semaphores can only be removed by the user that created them. If a different user tries to stop PI than the one who started it, you may run into this problem. If you get errors regarding accessing semaphores in the log file after trying to restart PI and ps -ef shows the bufserv application is not running, "su" to root and run bufutil -u.