FAQ

This page serves to collect frequently asked questions and corresponding answers. Please ask questions that are not answered here on the mailing list (and augment this list afterwards).

FAQ

I would like to write a real-time application that uses the LITMUS^RT API. Where should I start?

Have a look at the task bin/base_task.c in the liblitmus repository. It's a documented task skeleton that shows how to implement a periodic or sporadic real-time task.

Can I use pthreads with LITMUS^RT?

Yes. An example for a multithreaded real-time application is provided in bin/base_mt_task.c in the liblitmus repository.

I tried booting with one of the provided kernel configurations on my hardware, but the kernel kernel hangs during boot with the following message: "kernel panic not syncing vfs unable to mount root fs on unknown-block (0,0)". What's wrong?

This is a generic Linux problem, not a LITMUS^RT problem. The configuration is missing support for your root device and/or your root file system. To boot LITMUS^RT on your machine, you first need to have working configuration for an unmodified Linux kernel. Once you have mainline Linux working your machine, LITMUS^RT should boot without problems as well.

When testing with kvm using -nographic, the system appears to hang where normally a "login:" prompt would appear. However, I can log in via ssh. How can I enable local logins?

Your Linux distribution is not spawning a shell for the console. On distributions using /etc/inittab, you need to edit the inittab file to spawn a login process for console. Some distributions (such as Ubuntu and RedHat), do not use inittab. Instead, you must create a file named ttyS0 in /etc/events.d. Here is an example /etc/events.d/ttyS0 that works in Ubuntu 8.04:

start on runlevel 1
start on runlevel 2
start on runlevel 3
start on runlevel 4
start on runlevel 5

stop on runlevel 0
stop on runlevel 6

respawn
exec /sbin/getty -L 19200 ttyS0 vt102

Note that RedHat systems may use /sbin/agetty instead of /sbin/getty.

I am trying to boot a virtual test system in kvm, but I get the following error message (repeatedly).

hda: possibly failed opcode: 0x39
hda: task_pio_intr: status=0x41 { DriveReady Error }
hda: task_pio_intr: error=0x04 { DriveStatusError }

What is causing this?

This error message can occur if kvm cannot write to the image file that is backing hda. Check the file permissions.

I attempted to run liblitmus/rtspin, and got the following error

could not setup rt task params: Function not implemented

This error is caused when your liblitmus build is out of sync with your LITMUS^RT kernel build. Recompile LITMUS^RT followed by liblitmus to fix the problem.

I've followed the build instructions on the wiki, but the compilation fails. Why am I getting errors such as the following about request_exit_np_atomic()?

litmus/sched_plugin.c:85:4: error: implicit declaration of function ‘request_exit_np_atomic’ [-Werror=implicit-function-declaration]

This error is due to a typo in LITMUS^RT 2012.1 in include/litmus/litmus.h. This has been fixed in commit 6a00f206debf8a5c8899055726ad127dbeeed098. As a workaround, enable CONFIG_NP_SECTION in the kernel configuration.