Openstack CLI: Unset all variables beginning with prefix OS_

When using the Openstack CLI, you typically will get a shell script that you would source, which will export a bunch of variables to your session. I have run into the problem of switching between two different Openstack installs that were on different versions, and needed different variables. Also you will be need this when you will be generate parameters in different areas of scope for last version of keystone. Accordingly, the following example will unset all Openstack variables (all variables that begin with OS_)

Need create file reset_OS.sh with next content:

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#!/bin/bash
# ${!varprefix@} Matches all previously declared variables beginning with varprefix
unset ${!OS_@}

and use in next manner:

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$ . ./reset_OS.sh

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QEMU/KVM: Changing the default connect URI in libvirt

All the libvirt related commands, like virsh, virt-viewer or virt-install take a connect URI as parameter. The connect URI can be thought as specifying which set of virtual machines you want to control with that command, which physical machine to control, and how.

For example:

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virsh --connect "qemu+ssh://super@servers.arcade.click" start node011

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Supervisord: php script as pseudo-daemon

If and when you need to run a certain php script as a kind of daemon program, you can use the popular supervisord software package for this purpose.
Very often this will work much better, more efficiently and more conveniently as a replacement for clumsy php scripts in the system cron. Run the application in a short cycle, set the counter of time and repetitions – you’re done!

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CF: cf-cache-status headers explanation

When we are using Cloudflare in proxy mode, we see that the response headers contain invaluable information by lending insight into what’s really going on with our static object on pages.
This notice is small reminedr about the specifics of the cf-cache-status header, what its values mean.
It is very important in situations when you are making changes of css or js files and don’t see updates in window of browser, even if you are using suffixes for each URL.

When we work on site in production mode, each static object passthrough 3 level of caches before participation in rendering of page in browser:

  • cache plugin of WP(W3TC etc)
  • external caches of edge servers CF
  • local cache web browsers of clients

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