How to Read a Text File Few Lines at a Time Labview

Some usefull informations: http://www.ni.com/pdf/support/us/ni_linux_real-time_security_user_guide.pdf

Display some information on the command line

Using the tail role

This approach is probably the easier to implement and to understand.

You will write to a file (/tmp is a expert location) and read it using the tail function. This function, equally its proper noun suggest, read the tail of a file (or some piped information). We will use the -F pick to not be impacted past a rotation of the log("rotate" means delete or movement to another location etc.).

lvuser (the user that is used when you run an app) does not have all the permissions. Make sure that he is allowed to write to the file you lot chose.

On the LabVIEW side just right to a file, in this instance the file path is the post-obit:

On the Linux terminal, to subscribe to the log but enter the command:

$ tail -F /tmp/output.txt

You lot will become the following output (past default tail will start by displaying the concluding 10 lines of the file)

Remember that you lot are writing to a file. If you lot practice not stop the debug implementation or make some limitation on the size of your file, it can have some infinite on your disk...

Using TTY

This arroyo is a bit more deadening as you need to choose which terminal you desire to display the log and y'all need to modify the permission for lvuser.

Start follow this stride on the concluding:

In our instance theresponse shows we are continued to the device file at /dev/pts/0. Information technology'south likely that lvuser will non have access to this file. As lvuser is part of the group TTY that owns the device file, only add the following line to give hime the required permissions:

On the LabVIEW side run the following:

Y'all will see the same behavior as before but this time you don't need to run a control to outset information technology and you lot do not accept to worry about the file size. Even so yous will to do stride above every time yous shut the terminal.

As you granted the permission to the lvuser to brandish logs directly it means it can take over your panel every bit long as the application is running ( fifty-fifty if you lot press ctrl+C) :

Build and deploy without restarting the target

To deploy and build you tin can utilise direct the LabVIEW project or use the vi from the Application Builder Palette. To avert unsing 'Run as outset-up' that requires the reboot the target y'all can use the post-obit trick:

To do the following in one line:

ps -aef | grep -F {MainAppThread} | grep -v grep | grep -Eo -thousand 1 '[0-9]+' |head -one | xargs impale

First by entering the following command:

If it's the outset time you send the command you might accept an output that looks like this:

            2165 lvuser     0:00 /usr/bin/nirioserver  2723 lvuser     0:00 /usr/bin/nivisaserver  2762 admin      0:00 {lvrt-daemon} /bin/sh /etc/init.d/lvrt-daemon  2787 admin      0:00 /bin/su -- lvuser -l -c /etc/init.d/lvrt-wrapper NORMAL_START /var/run/lvrt_wrapper.pid imitation  2792 lvuser     0:00 {MainAppThread} ./lvrt  4281 admin      0:00 grep lv

The thread 2787 informs us that the current RT App as get-go normaly.

The thread 2792 is the RT App. By default if the thread is killed it will restart automatically. This is the characteristic we will utilize to avoid restarting the target. To kill information technology use the following command:

We use 2792 as it'south the current PID of the RT app thread.

Past running the control:

We detect the following:

            2165 lvuser     0:00 /usr/bin/nirioserver  2723 lvuser     0:00 /usr/bin/nivisaserver  2762 admin      0:00 {lvrt-daemon} /bin/sh /etc/init.d/lvrt-daemon  5224 admin      0:00 /bin/su -- lvuser -l -c /etc/init.d/lvrt-wrapper CRASHED_AND_RESTART /var/run/lvrt_wrapper.pid false  5225 lvuser     0:00 {MainAppThread} ./lvrt  5308 admin      0:00 grep lv

You can run into that the PID has changed and that the thread 5224 informs us that the awarding has crashed and restarted.

To summarize:

1. Build the app
2. Deploy it
3. Use the play a joke on to restart the app

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Source: https://readthedocs.web.cern.ch/display/MTA/%5BNILRT%5D+Troubleshoot+a+LabVIEW+RT+App

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