Get Virtual Machines from VMware with PySphere

This is a simple example of how to get a list of Virtual Machines from a VMware host, using PySphere.

{% highlight python %} import pysphere

server = pysphere.VIServer() server.connect('vmware.zindilis.net', 'username', 'password')

vms = server.getregisteredvms() for vm in vms: virtualmachine = server.getvmbypath(vm) print virtualmachine.getproperty('name'), virtualmachine.getproperty('ip_address') {% endhighlight %}

Bash Special Variables

A couple of notes on special variables available in the Bash shell.

$0: Name of the script

The special variable $0 contains the name of the script. It is useful when returning usage instructions to the user that run the script. For example:

{% highlight bash %} echo "Usage: $0 --option-1 --option-2"; {% endhighlight %}

$#: Number of arguments

The special variable $# contains the number of arguments passed to the script. If no arguments are passed, it is equal to 0. It is useful to examine the value of this variable before taking further actions, if a script must be run with a minimum number of arguments.

Here is an example of $# used together with $0:

{% highlight bash %} if [ $# -eq 0 ]; then echo "Insufficient number of arguments!"; echo "Usage: $0 /path/to/file"; fi {% endhighlight %}

$?: Most recent exit code

The special variable $? contains the exit code of the most recently executed command. It is useful to examine this to determine whether or not the previous command completed succesfully or returned an error.

Typically, commands that complete succesfully return an exit code equal to 0, with other values indicating different errors, but check each command's documentation to verify this.

In the following example, the existense of the word "test" in a file is checked:

{% highlight bash %} grep test /path/to/file > /dev/null; if [ $? -eq 0 ]; then echo "/path/to/file contains the word 'test'"; else echo "/path/to/file does not contain the word 'test'"; fi {% endhighlight %}

screen

Links

Enable EPEL Repository on CentOS 6

The most updated information for enabling EPEL should always be at the Fedora Project's Wiki.

In that page's section "How can I use these extra packages?", there are links to the latest versions for CentOS 6 (and CentOS 5).

In that page, download the .noarch file, for example:

wget http://www.mirrorservice.org/sites/dl.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm

Then, install with yum:

yum install epel-release-*.noarch

ntpdate

Troubleshooting no server suitable for synchronization

If you have a cron jon periodically running ntpdate to update the time on a system, you might at some point hit the no server suitable for synchronization error. You can gain some insight into the problem with running ntpdate with the -d option, which will show debugging output from the actions of ntpdate, without actually changing the time on the system.

One example cause of this issue is that the value of strata exceeds a maximum value, in which case the NTP server is rejected by the system as being too far from its own source. You should then focus on either fixing the NTP server itself, or changing your ntpdate target to another system.

Enable logging in MySQL

These are some haphazardly written notes on logging in MySQL. For consistency, create a new subdirectory in /var/log/ and assign ownership to the user under which your MySQL server is running - by default that would be the mysql user:

mkdir /var/log/mysqld/
chown mysql:mysql /var/log/mysqld

I like to name the directory mysqld instead of mysql, to clarify that the logs in that directory are those of the MySQL Server and not those of the MySQL Client.

Slow Query Log

The slow query log contains queries the execution of which took more than the value of the long_query_time variable, which by default is 10 seconds.

To enable the slow query log on the next start of mysqld, add the following line in your MySQL server's configuration file (/etc/my.cnf by default), in the [mysqld] section:

slow-query-log
slow_query_log_file=/var/log/mysqld/slow-queries.log

Create the file and assign ownership to the mysql user:

touch /var/log/mysqld/slow-queries.log
chown mysql:mysql /var/log/mysqld/slow-queries.log

Finally, either restart the server to enable the logging, or enable it on the already running server with:

mysql> SET GLOBAL slow_query_log_file='/var/log/mysqld/slow-queries.log';
mysql> SET GLOBAL slow_query_log=1;

In any of those cases, the values of the global variables slow_query_log and slow_query_log_file, should change from the default:

mysql> show variables like 'slow_query_log%';
+---------------------+----------------------------------+
| Variable_name       | Value                            |
+---------------------+----------------------------------+
| slow_query_log      | OFF                              |
| slow_query_log_file | /var/run/mysqld/mysqld-slow.log  |
+---------------------+----------------------------------+

To:

mysql> show variables like 'slow_query_log%';
+---------------------+----------------------------------+
| Variable_name       | Value                            |
+---------------------+----------------------------------+
| slow_query_log      | ON                               |
| slow_query_log_file | /var/log/mysqld/slow-queries.log |
+---------------------+----------------------------------+
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Hello, I'm Marios Zindilis and this is my website. Opinions are my own. You also find me on LinkedIn and GitHub.

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