AIX Distributed Shell (dsh) The NOT new but often
overlooked tool
Mohammad Almasri
4000 Legato Road
Suite 1100
Fairfax, VA 22033
Telephone 703.896.7620
IT-Solutions@five9group.com
AIX Distributed Shell (dsh) - The NOT new but often overlooked tool
By Mohammad Almasri
If you are an AIX system administrator, chances are you have multiple LPARs to manage on daily
basis.
If you have a need to type the same command into several machines at once, you can login to each
one with SSH and do it serially, or you can save yourself a lot of time and effort and use a tool like
dsh.
The dsh command runs commands concurrently on remote targets nodes (including Linux and the
different flavors of UNIX), hardware devices, or both and returns the output back to your current
terminal. Targets can be selected from multiple contexts. A context is a target database that contains
node and device definitions. The dsh command issues a remote shell command for each target
specified, and returns the output from all targets, formatted so that command results from all nodes
can be managed.
DSH is installed with AIX as part of the Cluster Systems Management (CSM) client file sets. These
file sets are necessary to support dynamic LPAR (DLPAR) operations in a partitioned AIX
environment. The actual dsh tool is installed as a symbolic link from /usr/bin/dsh to /opt/csm/bin/dsh,
via the csm.dsh fileset
NOTE: Starting with AIX 7.1, CSM is no longer supported or available. It has been replaced by
Distributed Systems Management (DSM). Section 5.2 of the IBM AIX 7.1 Differences Guide
Redbook provides details of the new DSM capabilities.
To use dsh you must configure your user environment appropriately. This involves two steps. First,
configure your SSH keys between the admin host and all of your remote hosts. While either rsh or
ssh can be used to execute commands on remote nodes, from a security perspective, I recommend
using ssh only. Many online tutorials explain the different ssh configuration options that allow you to
execute commands on another host without being prompted for a password.
Once you can execute a command on all your hosts without being prompted for a password, you're
ready to configure dsh.
Configuration
DSH requires that these environment variables are set within your shell (normally ksh):
$ env | egrep 'DSH|NODE_LIST'
DSH_NODE_RSH=/usr/bin/ssh
DSH_NODE_LIST=/home/user_name/aix
Place these entries in your .kshrc file:
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export DSH_NODE_RSH=/usr/bin/ssh
export DSH_NODE_LIST=/home/user_name/aix
export DSH_NODE_OPTS="-q"
The DSH_NODE_RSH variable indicates which remote command executable to use when dsh is
called. Set this to /usr/bin/ssh so that dsh will use the ssh command when connecting to remote
hosts.
The next variable is DSH_NODE_LIST. Known as the working collective, it points to a file that
contains a list of all the hosts that you want to execute a command on:
$ cat $DSH_NODE_LIST
lpar1
lpar2
lpar3
lpar4
The final variable, DSH_NODE_OPTS, is optional. It specifies which options are passed to the
remote command. Set this to "-q" so ssh runs as "ssh -q". This to suppress the ssh banner message.
Using dsh and Related Tools
From time to time you may need to execute commands on only some of your host systems. The "-w"
flag allows you to list the specific nodes on which to execute a command:
$ dsh –w lpar1,lpar2 date
lpar1: Tue Sep 16 16:40:31 EET 2008
lpar2: Tue Sep 16 16:40:30 EET 2008
Other tools are included with dsh. Some you may find useful include dcp, dping and dshbak. The
dcp command copies a file (or files) to multiple nodes in parallel. You will need to include the
following variables in your .kshrc file first, so that dcp will use scp as the file transfer method.
export DCP_NODE_RCP=/usr/bin/scp
export DCP_NODE_OPTS="-q"
The dping utility allows you to ping several hosts at once. It's useful for performing a quick "up or
down" health check on several systems:
$dping -n lpar1,lpar2,lpar3
lpar1: ping (alive)
lpar2: ping (alive)
lpar3: ping (alive)
The dshbak utility formats dsh command output, showing the hostname and output from the
command underneath:
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$ dsh –w lpar1,lpar2 date | dshbak
HOST: lpar1
---------------Tue Sep 16 16:40:43 EET 2008
HOST: lpar2
---------------Tue Sep 16 16:40:43 EET 2008
To view the current settings for your dsh environment, execute dsh with the "-q" flag:
$ dsh -q
DSH:DCP_DEVICE_OPTS=
DSH:DCP_DEVICE_RCP=
DSH:DCP_NODE_OPTS=-q
DSH:DCP_NODE_RCP=/usr/bin/scp
DSH:DSH_CONTEXT=
DSH:DSH_DEVICE_LIST=
DSH:DSH_DEVICE_OPTS=
DSH:DSH_DEVICE_RCP=
DSH:DSH_DEVICE_RSH=
DSH:DSH_ENVIRONMENT=
DSH:DSH_FANOUT=
DSH:DSH_LOG=
DSH:DSH_NODEGROUP_PATH=
DSH: DSH_NODE_LIST=/home/user_name/aix
DSH:DSH_NODE_OPTS=-q
DSH:DSH_NODE_RCP=
DSH:DSH_NODE_RSH=/usr/bin/ssh
DSH:DSH_OUTPUT=
DSH:DSH_PATH=
DSH:DSH_REPORT=
DSH:DSH_SYNTAX=
DSH:DSH_TIMEOUT=
DSH:RSYNC_RSH=
DSH isn't a replacement for having a configuration management system or any of the other best
practices when managing a number of machines. However, if you need to do something quickly
outside of your usual toolset or process, dsh is indispensable. It can save a lot of time when doing
tasks that need to be done on more than one machine, but like any power tool, it can cause a lot of
damage if used haphazardly. Always make sure you have the correct target servers in your
$DSH_NODE_LIST variable and I would recommend running a "read only" type of command, e.g.
uptime before I execute any commands that will modify the system settings on the target clients.
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