Tag Archives: automation

GNU and UNIX Commands: Using a while Loop to Populate Configuration File

I recently had a need to generate a lot of Nagios host definitions. The hosts all had a similar naming convention:

foo-nnnnprjenv

Here, nnnn was a zero-padded number from 0 to 9999. In this particular environment, there were 41 hosts. A simple multiline echo command inside a while loop fed by seq produces the appropriate host stanzas we can add to our Nagios configuration. We also look up the servers IP addresses via the host command and insert those too:

$ seq -w 1 41 | while read num; do
   echo "define host {
        use             generic-host
        host_name       foo-00${num}prjenv
        alias           foo-00${num}prjenv
        address         $( host foo-00${num}prjenv | awk '{print $NF}' )
        register        1
}
"
done

$ seq -w 1 41 | while read num; do

echo "define host {

use generic-host

host_name foo-00${num}prjenv

alias foo-00${num}prjenv

address $( host foo-00${num}prjenv | awk '{print $NF}' )

}

done

The -w option to seq causes it to output a leading-zero padded number. Redirect the output of this loop to a file, and you’ll have your Nagios host configuration. This is another reasons why having a naming convention for a large number of servers is important - it will aid you in automation and administration down the track.

Script: add_users.sh

Script Name

add_users.sh

Script Summary

Add users to a system en-masse.

Script Description

This script will read a list of space separated Firstname Lastname entries, one per line, from a file specified. It will create an appropriate group (specified within the script) to add users to if it doesn’t already exist. If the group does exist, the users will be created via useradd and a random password set, and those passwords outputted to STDOUT.

Script Limitations

Only tested on RHEL/OEL/CentOS 5.x and 6.x.
Will handle duplicate usernames semi-gracefully by exiting with an error, rather than doing anything fancy - you’ll need to add those users manually

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An Introduction to Solaris 11 Zones

Solaris Zones (or Containers) were first introduced in Solaris 10. I wrote about them a while back in How to Get Started with Solaris Containers, but a lot has changed in Solaris 11. Solaris Zones provide an easy way to either provide a sparse chroot-like environment so that applications can run in an environment that will not be detrimental to global system resources, or a full branded environment (running a Solaris 10 branded zone, for example). Delegated administration can be configured so that a zone can be managed by someone other than the global sysadmin. Zones provide an excellent way to split a system into several logical units, each with their own filesystem resources, system resources and management. Most of what I wrote about previously is still very pertinent, but Solaris 11 has built upon zone technology, placing it at its very core.

In Solaris 10, the default IP type for zones was shared, which meant that the zone shared the IP stack with the global zone. Within a zone on Solaris 10, an administrator was unable to configure network settings, unless exclusive IP was used, in which case the zone would be bound to a physical NIC in the global zone, and that NIC would only be available for exclusive use by that zone. With Solaris 11, and virtual networking, all zones can be created with an exclusive IP type. A Virtual NIC (VNIC) is created for each zone, over some physical NIC on the global zone. This network virtualisation allows each zone to maintain its own TCP/IP stack, and the zone administrator can change the zone’s network configuration from within the zone itself. A new anet interface type has been introduced within zonecfg to handle this.

Solaris 11 zones are now provisioned using the new Image Packaging System (IPS) and in a default configuration, packages will be installed from the repository configured (http://pkg.oracle.com, for example) in the global zone. It would make sense to have a local repository if you were rolling out large numbers of systems or zones, but for our testing purposes, downloading a couple of hundred megabytes of packages is no big issue.

This article will walk through the creation of a simple Solaris 11 zone, and introduce a method of installing zones without operator intervention using System Profiles.