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QNX Software Development Platform
QNX SDP is a cross-compiling and debugging environment, including an IDE and command-line tools, for building binary images and programs for target boards running QNX Neutrino 7.1.
OS Components & Operations
User's Guide
The QNX Neutrino User's Guide is intended for all users of a QNX Neutrino RTOS system, from system administrators to end users.
Understanding System Limits
Resources on a system tend to be finite (alas!), and some are more limited than others. This chapter describes some of the limits on a QNX Neutrino system.
Other system limits
Message queues
The number of message queues is limited by the -n option to mqueue or mq. The default is 1024, and the maximum is 32768; you can query the current value with sysconf( _SC_MQ_OPEN_MAX ).

QNX Momentics IDE User's Guide
This User's Guide describes version 7.1 of the Integrated Development Environment (IDE) that's part of the QNX Momentics tool suite.
QNX Software Development Platform
QNX SDP is a cross-compiling and debugging environment, including an IDE and command-line tools, for building binary images and programs for target boards running QNX Neutrino 7.1.
- Quickstart Guide
- OS Components & Operations
  - Adaptive Partitioning User's Guide
  - Boot Optimization Guide
    The Boot Optimization Guide describes techniques you can use to reduce the time from your board's initial power on until you have a fully functional QNX system running on the board.
  - Building Embedded Systems
    The Building Embedded Systems guide is intended for developers who are developing or building BSPs for QNX Neutrino RTOS embedded systems.
  - Core Networking Stack User's Guide
    This guide introduces you to the QNX Neutrino Core Networking stack and its manager, io-pkt.
  - Customizing a BSP
    While QNX provides Board Support Packages (BSPs) for many common platforms and their individual variants, in some cases, you need a BSP for a board that QNX does not provide. If this is the case, you can modify a QNX BSP or develop your own.
  - Device Publishers Developer's Guide
  - High Availability Framework Developer's Guide
  - High-Performance Networking Stack (io-sock) User's Guide
    This guide contains instructions for implementing and using the QNX Neutrino High-Performance Networking Stack and its manager, io-sock.
  - Instant Device Activation
  - Migrating to QNX SDP 7.1
  - PCI Server User's Guide
  - Persistent Publish/Subscribe Developer's Guide
  - Platform-independent Publish/Subscribe Developer's Guide
    This guide is intended for application developers who want to use the Platform-independent Publish Subscribe (PiPS) framework to exchange information with other applications. First, the overall PiPS design and data-exchange model are explained. Then, tutorials on using PiPS are given. These tutorials cover key tasks such as selecting a publish-subscribe provider to use and writing plugins that read and write custom data types.
  - QDB Developer's Guide
  - QNX Helpers Developer's Guide
    These libraries provide QNX helpers, including helpers that assist with logging, string conversion, and number and type sizes.
  - SMMUMAN User's Guide
  - System Analysis Toolkit (SAT) User's Guide
  - System Architecture
    The System Architecture guide accompanies the QNX Neutrino RTOS and is intended for both application developers and end-users.
  - Technotes
  - User's Guide
    The QNX Neutrino User's Guide is intended for all users of a QNX Neutrino RTOS system, from system administrators to end users.
    - Getting to Know the OS
      Welcome to the QNX Neutrino RTOS!
    - Logging In, Logging Out, and Shutting Down
      QNX Neutrino is a multiuser operating system; it lets multiple users log in and use the system simultaneously, and it protects them from each other through a system of resource ownership and permissions.
    - Managing User Accounts
      This chapter explains how user accounts work, how users can change their password by using the passwd utility, and how system administrators can use the passwd utility and edit account database files to create and maintain users' accounts.
    - Using the Command Line
      Like QNX 4, Unix, and DOS, the QNX Neutrino RTOS is based on a command-line interface that you might want or need to use instead of the GUI.
    - Working with Files
      In a QNX Neutrino system, almost everything is a file; devices, data, and even services are all typically represented as files. This lets you work with local and remote resources easily from the command line, or through any program that works with files.
    - Using Editors
      An editor is a utility designed to view and modify files.
    - Configuring Your Environment
      The Controlling How QNX Neutrino Starts chapter describes what happens when you boot your system, and what you can do to customize the system. This chapter describes how you can customize the environment that you get when you log in, and then describes some of the setup you might need to do.
    - Writing Shell Scripts
      Shell scripting, at its most basic, is taking a series of commands you might type at a command line and putting them into a file, so you can reproduce them again at a later date, or run them repeatedly without having to type them over again.
    - Working with Filesystems
      The QNX Neutrino RTOS provides a variety of filesystems, so that you can easily access DOS, Linux, as well as native Power-Safe disks.
    - Using Qnet for Transparent Distributed Processing
      A QNX Neutrino native network is a group of interconnected computers running only the QNX Neutrino RTOS. In this network, a program can transparently access any resource—whether it's a file, a device, or a process—on any other node (computer) in your local subnetwork. You can even run programs on other nodes.
    - TCP/IP Networking
      The term TCP/IP implies two distinct protocols: TCP and IP. Since these protocols have been used so commonly together, TCP/IP has become a standard terminology in today's Internet. Essentially, TCP/IP refers to network communications where the TCP transport is used to deliver data across IP networks.
    - Backing Up Data
      No matter how reliable your hardware and electrical supply are, or how sure you are that you'll never accidentally erase all your work, it's just common sense to keep backups of your files. Backup strategies differ in ease of use, speed, robustness, and cost.
    - Securing Your System
      Now that more and more computers and other devices are hooked up to insecure networks, security has become a very important issue. The word security can have many meanings, but in a computer context, it generally means preventing unauthorized people from making your computer do things that you don't want it to do.
    - Fine-Tuning Your System
      This chapter describes how you can improve your system's performance.
    - Understanding System Limits
      Resources on a system tend to be finite (alas!), and some are more limited than others. This chapter describes some of the limits on a QNX Neutrino system.
      - Configurable limits
        When you're trying to determine your system's limits, you can get the values of configurable limits, special read-only variables that store system information.
      - Filesystem limits
        Under the QNX Neutrino RTOS, filesystems aren't part of the kernel or core operating system; they're provided by separately loadable processes or libraries.
      - Other system limits
        File descriptors
        The total number of file descriptors has a hard limit of 32767 per process, but you're more likely to be constrained by the -F option to procnto or the RLIMIT_NOFILE system resource. The default value is 1000; the minimum is 100.
        Synchronization primitives
        There are no limits on the number of mutexes and condition variables (condvars).
        TCP/IP limits
        Shared memory
        The number of shared memory areas is limited by the allowed virtual address space for a process, which depends on the target architecture.
        Message queues
        The number of message queues is limited by the -n option to mqueue or mq. The default is 1024, and the maximum is 32768; you can query the current value with sysconf( _SC_MQ_OPEN_MAX ).
        Platform-specific limits
    - Technical Support
      If you have any problems using QNX Neutrino, the first place to look for help is in the documentation.
    - Glossary
    - Examples
      This appendix includes samples of some of the files described in this guide.
- Audio & Graphics API
- Multimedia
- Networking Middleware
- Programming
- Sensor Framework
- System Security Guide
  The QNX System Security Guide is intended for both system integrators who are responsible for the security of a QNX Neutrino RTOS system and developers who want to create a QNX Neutrino resource manager free from vulnerabilities.
- Utilities & Libraries
QNX Hypervisor
The QNX Hypervisor allows you to run multiple OSs on a target system so you can separate critical and non-critical functions, support a wide variety of applications, and reduce hardware costs.
QNX Software in the Cloud
QNX Software in the Cloud enables developers to use the QNX software in Amazon Web Services (AWS) and Microsoft Azure (Azure).
QNX Advanced Virtualization Frameworks User's Guide
This User's Guide is aimed at all systems integrators and developers who want to design and build embedded systems using the QNX Advanced Virtualization Frameworks.
Typographical Conventions, Support, and Licensing
This section describes the typographical conventions used throughout the documentation and explains how to obtain technical support.

Message queues

The number of message queues is limited by the -n option to mqueue or mq. The default is 1024, and the maximum is 32768; you can query the current value with sysconf( _SC_MQ_OPEN_MAX ).

The default maximum number of entries in a queue, and the default maximum size of a queue entry depend on whether you're using the traditional (mqueue) or alternate (mq) implementation of message queues:


Attribute	Traditional	Alternate
Number of entries	1024	64
Message size	4096	256

For more information, see mqueue and mq in the Utilities Reference, and mq_open() in the QNX Neutrino C Library Reference.

Note:

In the traditional implementation, each call to mq_open() uses one file descriptor; in the alternate implementation, each call to mq_open() uses two.

Page updated: March 12, 2026