Cart Using VNC to Speed Up Slow X-forwarded Sessions
Most of you know that you can use X-forwarding built into SSH to run a graphical application on a remote host: laptop$ ssh -X head.mycluster head$ firefox & (Firefox session displays on your laptop, running on the remote host) But sometimes these programs run very slowly over the network. Firefox can be slow to render, […]
Use Screen to Run Long Processes
Tech TipScreen is a Linux utility that allows you to run multiple terminals all within a single terminal window manager. It can be used for many things and greatly increases workflow. Screen enables you to run your long scripts/processes within a screen session. If you want to execute a script that generally takes a very […]
Keep an Eye on Your RAID Status
Our customers frequently order systems with two hard drives to hold a RAID 1 volume mirroring the OS filesystems. This is done with Linux software RAID, and it’s important to periodically check the health of the drives. To do this, run cat /proc/mdstat. If all volume members are working properly, you should see [UU]. For […]
How to identify and prevent overheating
How to identify and prevent overheating Symptoms of Overheating Turning off on its own Freezing Frequent memory errors Most commonly a computer that is overheating will turn off unexpectedly, and repeat the behavior shortly after being turned back on. What causes this behavior is that the CPU temperatures are always monitored and the system will […]
Adding new nodes to an existing cluster
The following steps apply if you are adding in new nodes to your cluster and these nodes will be cloned from your existing nodes image. First edit /act/etc/act_nodes.conf and add your new node definitions below the existing node definitions. If you do not have these already they can be provided by ACT support. Next edit […]
Update Initrd
Have you blacklisted a kernel module, but it’s still showing up at boot? You probably need to update your initrd, a compressed filesystem used to bootstrap the OS. Simply run “dracut –force”, and the initrd will be recreated, taking into account any configuration changes made in your /etc filesystem. Then reboot. Your changes are now […]
Identifying Issues with Network Connectivity
Network connectivity can cover many different areas, and diagnosing which area your problem lays in is the first step to fixing the problem. Below we will cover multiple steps for identifying a problem. Verify connections and LEDs Verify that the network cable is properly connected to the back of the computer and at the switch. […]
How do I tune my HPL.dat file?
Tuning HPL can be a long and difficult process. Once you’ve found the perfect BLAS library for your architecture, now you need to create a perfect HPL.dat file. Use the form below and generate an output file as a starting point on getting the best GFLOP number you can out of your cluster. Input Nodes: […]
Troubleshooting OpenMPI Invocation Problems
OpenMPI works with a large number of transport mechanisms, from shared memory on the local machine, to IP over Ethernet or even RDMA over InfiniBand. With default settings, when you start your program using mpirun, OpenMPI will choose the best interface available.. Unfortunately, the logic isn’t foolproof, and sometimes you will hit snags and your […]
Standard Cluster – InfiniBand Networking
This is the InfiniBand configuration for most of the HPC clusters we build.
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