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

• Introduction
• Usage
• Examples

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

• cexec is the parallel version
• cexecs is the serial version. The serial version of cexec is useful for debugging a cluster (each node is executed and printed before the next node is run).

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

• --help -h  -- display help message

   

• --file -f <filename>  -- alternatative cluster configuration file, which will be used instead of /etc/c3.conf

   

• -i   --- interactive mode, ask once before executing

   

• --all   -- execute on all the nodes in all the clusters in the c3.conf file, note this ignores the [MACHINE_DEFINITIONS] block

   

• --head  -- execute command on head node, does not execute on compute nodes

   

• --pipe -p  -- formats the output in a pipe friendly fashion. It prepends the cluster name, a space, the node name and a colon before each line of output.

   

• --all   -- execute command on all nodes in all clusters that are accessible. When specifying --head  only the head nodes will participate. This ignores the [MACHINE_DEFINITIONS] section.

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

NEWS CONTENTS

• 200102 : Manpage of C3-SCALE ( Manpage of C3-SCALE, )

Old News ;-)

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

Recommended Links

Softpanorama Recommended

Top articles

Sites

Top articles

Sites

• cexec(1),
• c3(1),
• cget(1),
• ckill(1),
• cpush(1 ),
• cpushimage(4),
• crm(1),
• cshutdown(4),
• cname(1),
• cnum(1),
• clist(1),
• c3.conf(5),
• c3-scale(5)

Index

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

GENERAL

SETUP

ENVIRONMENT

FILES

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Last modified: March 12, 2019