ACT knowledge base

10 most recent knowledge base articles

Tech Tip: Installing Libraries for Python in Your System Directories

  Python is being used more frequently in HPC applications. Whether a job is being run by the scheduler or pre/post-processing on login nodes, there’s a chance you may run into it. With Python comes the need for libraries. Installing the libraries in system directories normally isn’t possible, but there is a good solution for …

 

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 …

 

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 …

 

Keeping the Shell from Hanging Up After You Log Out or Disconnect

Have you ever started running something on a remote machine, only to realize that it won’t complete before you need to close your SSH connection? Running a screen session is nice, but what do you do if you didn’t start one? Have no fear – we can keep the shell from hanging up the job …

 

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 …

 

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 clusters we build.

 

Getting package information

By using the ‘rpm’ command (RPM Package Manager) is is possible to get a lot of information about installed packages on your system. To start, say we want to see if we have a specific package name installed on our system. We can search all the currently installed packages for a package named ‘actutil’ by: …

 

Changing Contents in a File in Every Node

Occasionally you may want to change a a single string inside of a file that is on every compute node. If the file was the same on every node you could change it in one place and then copy it out like so: $ act_cp -g nodes /path/to/file Some config files are unique to each …

 
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