The LabVIEW Real-Time Module executes VIs on the NI Linux Real-Time operating system. However, special considerations must be made when working with this real-time operating system.

Special Considerations

Keep the following considerations in mind when using an NI Linux Real-Time target. You also can visit ni.com/info and enter Linux to learn more about the NI Linux Real-Time operating system.

General

• The FTP server is disabled by default, and you cannot use it in safe mode. NI recommends using WebDAV as the file transfer mechanism for improved security.
• Virtual memory is supported, which implies the following:
  • A process crash restarts the process without restarting the target.
  • Monitoring the largest contiguous memory block does not provide useful or necessary information on NI Linux Real-Time targets.
• System Exec VI is supported.
• Time zone changes do not require a target restart.

File System and Directory Structure

• The file system is case-sensitive.
• Directory paths display in Linux format. For example, paths use forward slashes and do not contain drive letters.
• NI Linux Real-Time targets enforce file and folder access permissions. Refer to the KnowledgeBase article Working with File Paths on Real-Time Targets for information about these permissions.
• The RTOS deletes the content in the temporary folder /tmp on target restart. The temporary folder allocates space from RAM up to a maximum size of 64 MB.
• The c:\ni-rt directory does not exist on NI Linux Real-Time targets. Refer to the KnowledgeBase article Working with File Paths on Real-Time Targets for information about the directory mapping on NI Linux Real-Time targets.
• Direct modification of the ni-rt.ini configuration file is highly discouraged. Modification of this file may result in incorrect system behavior.
  Note Some NI troubleshooting procedures require manual edits to this file. Take care to precisely follow troubleshooting documentation in these scenarios.

Web Services

• WebDAV is enabled by default.
• SSL is enabled by default.
• NI Web-based Configuration & Monitoring is available in safe mode.
• It is only possible to configure a target reachable via IP address (DHCP, link-local, or static). mDNS is used for target discovery.
• You cannot use the Console Out using NI Web-based Configuration & Monitoring on NI Linux Real-Time targets. Instead, connect your NI Linux Real-Time targets to a computer using a serial port to view the output of the Console Out. Refer to the KnowledgeBase article Console Out on cRIO, sbRIO and cFP Controllers for detailed information about how to use the Console Out.

Authentication

• You can log in to a target using NI Web-based Configuration & Monitoring, SSH, or a serial connection. Refer to your hardware documentation to learn about enabling SSH on your RT target.
  Note NI recommends you set a password to log in using SSH or a serial connection.
• To reset a forgotten administrator password, you must physically access the target and reset all settings to the factory default. Contact NI for assistance with this process.
• Your target creates an admin user that is equivalent to the root user in Linux systems.

  Caution Do not create users in NI Web-based Configuration & Monitoring with the same name as system accounts. For example, do not create a user named root or ssh. Doing so overwrites the system account.

• SSH supports public keys as an alternate form of authentication.

Security

• Visit ni.com/info and enter RTSecurity to keep informed about security as it relates to NI products.

Unsupported Features

The LabVIEW Real-Time Module does not support certain LabVIEW features for VIs that run on RT targets. For instance, if you attempt to deploy and run a VI that has unsupported functionality on an RT target, the VI might still execute. However, the unsupported functions do not work and return standard LabVIEW error codes. The LabVIEW Real-Time Module does not support the following features on RT targets that run the NI Linux Real-Time RTOS:

• ActiveX VIs
• NI TestStand VIs (ActiveX-based)
• .NET VIs
• Report Generation VIs
• Windows Registry Access VIs
• Report Express VI (Uses the unsupported Report Generation VIs)
• Graphics & Sound VIs
• Database Connectivity VIs
• Menu functions
• Cursor VIs
• IrDA functions
• File System Web Service LabVIEW API
• Call Library Function Nodes that access an operating system API other than NI Linux Real-Time
• Open/Create/Replace File function interactively using a file dialog box
• Clear indicators when called option of the Execution Properties page
• Auto Configure option of the Create Histogram Express VI
• Certain Advanced TDMS functions
• Profile Buffer Allocations window
• Largest Available Memory Block Property Node—This property node does not provide useful information for NI Linux Real-Time targets and returns an error if used. Use the Free Physical Memory property node instead.
• Latch Until Released and Switch Until Released Boolean mechanical actions—Refer to the KnowledgeBase article Boolean "Until Released" Mechanical Action Not Supported on Real-Time Targets for information about why these Boolean mechanical actions do not work on RT targets.

Modifying Front Panel Objects of RT Target VIs

When a VI or stand-alone application runs on a headless RT target or if you disable the embedded UI, you cannot execute VIs that modify a front panel. For example, you cannot change or read the properties of front panel objects with property nodes because there is no front panel for VIs that run on the RT target. The VI still runs on the RT target but the front panel object is not affected and returns an error. In some cases, you can establish a front panel connection with the RT target to use some unsupported LabVIEW features. Right-click an RT target in the Project Explorer window and select Connect from the shortcut menu to open a front panel connection with the target.

The following features only work on an RT target with a front panel connection:

• Front panel property nodes and control references.
  Note An RT target updates the values of property nodes and control references asynchronously, meaning a property node or control reference might not contain the latest value of the indicator or control.
• Dialog VIs and functions
• VI Server front panel functions

Real-Time Module and Express VI Considerations

LabVIEW Express VIs increase LabVIEW ease of use and improve productivity with interactive dialog boxes that minimize programming for measurement applications. Express VIs require additional performance overhead during execution; therefore, do not use Express VIs in deterministic or processor-intensive applications. Instead, develop real-time applications with standard LabVIEW VIs.

Debugging Reentrant VIs

LabVIEW debugging tools are not available for copies of reentrant VIs executing on RT targets. Because LabVIEW identifies copies of reentrant VIs by their front panels and VIs executing on RT targets do not include front panels, LabVIEW cannot open reentrant VI copies for debugging. However, you can run and debug your application on Windows prior to deploying the application to the RT target.