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cexec - A utility that executes a given command on each node of a cluster

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Introduction

cexec  is a utility that executes a given string on each node of a cluster.  syntax somewhat imitates ssh syntax (cluster:nodes)

This command is intended to be a general purpose utility for executing command on mutil servers. It has no real connection to HPC clusters, as such.

Cexec exists in two version

TIP: In case command contains double quote the whole command should be put in single quotes -- probably bug in cexec

cexec 'useradd -u 1003 -g 1003 -c "Medea application" -d /Apps/MD medea'

Usage

cexec(s)  [OPTIONS] [MACHINE DEFINITIONS] command

Examples

There are several basic ways to call cexec:

1. To simply execute a command on the default cluster:

 
cexec mkdir temp
 

this creates a directory named temp in your home directory

2. To execute a command on a subset of nodes on the default cluster

 
cexec :2-6 ls -l
 

this executes ls with the -l option on nodes of the first listed (default) cluster

3. To execute commands on a list of clusters

 
cexec cluster1: cluster2: ls -l
 

this executes ls with the -l option on all the nodes in both clusters

4. Quote position is important  if can you use pipes or other special symbols

 
cexec "ps -aux | grep root"
 

will execute ps on each node, grep for root there, sort the output, and display it on the screen
 

cexec ps -aux | grep root
 

will execute ps on each node, sort the output, grep out all the lines with root, and only display those lines to the screen. This removes all the formatting, to use C3 in this method the --pipe option should be used

Configuration files

/etc/c3.conf

 
This file is the cluster configuration file that contains the names of the nodes to which commands will be sent. The cluster configuration file of nodes may also be specified from the command line. The format of both files is identical.
 
see the c3.conf(5) man page for the format

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Manpage of C3-SCALE

These examples will assume that the staging node includes itself in the responsibilities list. In the case where it is not included it would require an extra command so that the execution will take place on both the staging nodes and it's list of responsibilities. The most important option common throughout the C3 commands is the --all option. This option tells C3 to execute the given command on each and every cluster and node in the configuration file. It is recommended that the most commonly used or perhaps all of the C3 command be aliased to "command --all" for convenience. The following command will push /etc/passwd to every node in the scalable cluster:

cpush --all /etc/passwd

The other option is to explicitly list each sub-cluster on the command line. However, for large clusters this would be quite cumbersome if not impossible to do without human error. At this point using ranges on a scalable cluster is not as clean as using them on a non-scalable cluster. Because "node48" could be in any of the sub-clusters, or "node35-64" may cross several sub-cluster boundaries. These must be explicitly searched on and explicitly stated on the command line. For example searching in the first scalable configuration file:

cname --all node48 node35 node64

will return node 48 in part6 position 7, node35 in part5 position 1, node64 in part8 position 8. To execute on node48 use:

cexec part6:7 hostname

to execute on 35-64 use:

cexec part5:1-7 part6: part7: part8: hostname

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Index

NAME
SYNOPSIS
DESCRIPTION
OPTIONS
GENERAL
SETUP
ENVIRONMENT
FILES
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Last modified: September 12, 2017