feat(post): parallel shell

Author: SyntaxRules

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_posts/2016-12-03-welcome-to-jekyll.markdown

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+---
+layout: post
+title:  "Parallel Shell Utilities"
+tags: hpc software utilities
+---
+
+> The most fundamental tool needed to administer a cluster is a parallel shell, which allows you to run the same command on a series of nodes.
+>
+> [Linux Magazine](http://www.linux-magazine.com/Issues/2014/166/Parallel-Shells)
+
+
+There are 3 popular ways to perform parallel actions on HPC clusters:
+- Using a shell script
+- Using Pdsh
+- Using ClusterShell
+
+No extra installation is needed to use the shell script method but you'll have to install Pdsh and ClusterShell if you want to use them. The [OpenHPC stack](https://github.com/openhpc/ohpc) comes with them pre-packaged. I won't be going over how to install them, but installation is simple with provided package managers.
+
+Before we dive into these 3 methods, its important to note that you should have ssh set up to authenticate with ssh keys, instead of a password for this to work. Don't skip this, or your'll have to enter your password way too many times!
+
+## Using a shell script
+This method can be done with any scripting language, but I'll use bash.
+
+Create a script that you want ran:
+```
+#!/bin/bash
+
+# You will need to run this script on a passwordless account!
+
+for NODE in node1 node2 node3
+do
+    ssh $NODE uptime
+done
+```
+
+And run it with `sh your-script.sh`. This will run your command on all nodes, one at a time, printing everything to the screen.
+
+## Using Pdsh
+
+> "Pdsh is a multithreaded remote shell client which executes commands on
+ multiple remote hosts in parallel."
+>
+> [Pdsh Github](https://github.com/grondo/pdsh)
+
+Using pdsh is simple enough:
+```
+# perform th uptime command on node1, node2, node3 and node 4
+$ pdsh -w node[1-4] uptime
+node1: 19:01:18 up 1 day, 19:19,  1 user,  load average: 0.29, 0.57, 0.53
+node2: 19:11:25 up 1 day, 19:19,  1 user,  load average: 0.29, 0.57, 0.53
+node3: 19:19:11 up 1 day, 19:19,  1 user,  load average: 0.29, 0.57, 0.53
+node4: 19:20:45 up 1 day, 19:19,  1 user,  load average: 0.29, 0.57, 0.53
+```
+
+
+## Using ClusterShell
+
+ClusterShell is built and maintained by CEA-HPC and claims to be effective on supercomputers with 5,000 compute nodes. Using ClusterShell is very similar to pdsh
+```
+$ clush -w foo[1-5] echo "Hello World"
+```
+ClusterShell does some merging of outputs and does a better job of handling hanging nodes than pdsh.
+
+## References
+
+[Bash for loop Syntax](https://www.cyberciti.biz/faq/bash-for-loop/)
+[Pdsh github](https://github.com/grondo/pdsh)
+[Pdsh man page](https://linux.die.net/man/1/pdsh)
+[Pdsh vs ClusterShell](https://github.com/cea-hpc/clustershell/wiki/Pdsh)
+[ClusterShell Github](https://github.com/cea-hpc/clustershell)
+[ClusterShell main page](http://cea-hpc.github.io/clustershell/)