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Similarly to message queues, pipes offer another mechanism for intertask communication. An unnamed pipe is typically used between processes that are related by either a parent-child relationship or a sibling relationship. A named pipe is a persistent file object, which is typically used between processes that are not necessarily related. Each pipe has two ends, one for writing and one for reading. The read operation on a pipe can be blocked if the pipe is empty, and the write operation on a pipe can be blocked if the available space is not sufficient to hold the data to be written. In a POSIX-compliant operating system implementation, the write operation on a pipe is atomic when the data to be written are no more than the maximum capacity defined by PIPE_BUF. The POSIX select operation allows a task to simultaneously block on several pipes until any one of them becomes ready for reading or writing.

Publisher Summary Nagios 3 has many performances, object configuration, and CGI front-end enhancements. Object configuration inheritance has improved and extended. Objects are the defined monitoring and notification logical units within a Nagios configuration. The objects that make up a Nagios configuration include services, service groups, hosts, host groups, contacts, contact groups, commands, time periods, notification escalations, notification dependencies, and execution dependencies. Nagios supports service and host dependencies with service and host escalations. One can add arbitrary custom variables to services and hosts and access those variables in notifications and service and host checks. In addition, the CGI front end has special sub tabs for unhandled service, host, and network problems. The performance data output subsystem is very flexible and can even write to named pipes. The Nagios event broker (NEB) subsystem has been improved and enhanced. A number of new performance tuning features and tweaks can be used to help optimize the performance of Nagios installation.