OSX Open Command – Launch Custom Application

The OSX “open” command line tool is very useful.  Use it to launch a URL or point to a folder and the web browser or Finder pops up automatically.  But what about when you want to launch a particular app to handle a resource you provide?  It can do that as well.  Easily.

In this example I’m setting up my environment to launch several Windows remote desktop client sessions using the wonderful CoRD application.  The idea is that I can put the CoRD app in a folder with a shell script and have an easily transportable launcher package to give to others – without them having to install a RDP client, etc.

Because I’m not install the CoRD application globally, the RDP protocol doesn’t get associated with the app.  Therefore, when using the open command I need to explicitly tell it what application to launch it with, using the “-a” flag:

The benefit to using the open command here is that it won’t launch new CoRD instances, but will add them as sessions to the existing one.  Likewise, open will start the process and return you to the command line – so you can list several open statements in a script and it will run them all without having to do any funky backgrounding step.

Thanks to this old OSXDaily post for pointing me in the right direction.  I had given up on the command because I didn’t realise there were more options.  Next time I’ll read the manual first!



Google wants “mobile-friendly” – fix your WordPress site

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Google mobile check fixed success

TheNextWeb reports: “Google will begin ranking mobile-friendly sites higher starting April 21“.  It’s always nice having advance warning, so use it wisely – here’s how to tweak WordPress to increase your mobile-friendliness.

Google Mobile-Friendly Check

I use a self hosted WordPress site and wanted to make sure it was ready for action.  I already thought it was, because I’ve accessed in on a mobile device very often and it worked okay.

I even went onto the Google Web Admin tools and the mobile usability check said things were fine, but… Continue reading “Google wants “mobile-friendly” – fix your WordPress site”

iPhone cable – loose connection?

iPhone cable – mysterious loose connection bothering you?  Before buying a new gold plated cord or adapter, clean out the port with a toothpick.  You will be amazed!

HP Scanning on OSX Yosemite [SOLVED]

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Vuescan website
Vuescan website

Vuescan website
Vuescan website
It was time to solve my HP scanning problem on OSX Yosemite.  My HP LaserJet CM1312 MFP – multifunction printer is getting a bit old, or at least HP’s support is falling by the wayside. Don’t bother with the HP software as it’s for 10.7. It did work at one point on this laptop but then totally gave up.

I spent too long trying to find new drivers that enable scanning, with no luck, until I found Vuescan.  It’s a free trial (with watermark).  I’m sure it supports lots of scanners, just get it and see before paying.

After a $29 Paypal and 7MB download I was scanning instantly – didn’t even have to point it to my printer.


Twitter cards made easy in WordPress

Just a note to self and others using WordPress – the Yoast WordPress SEO plugin did the trick to get Twitter cards working well – with only a couple clicks.   If you are tempted to hack your own HTML headers, you are going the wrong direction – follow this tutorial instead: http://www.wpbeginner.com/

Thanks WPBeginner and Yoast!

Supertunnels with SSH – multi-hop proxies

I never know what to call this process, so I’m inventing the term supertunnels via SSH for now. A lot of my work these days involves using clusters built on Amazon EC2 cloud environment. There, I have some servers that are externally accessible, i.e. web servers. Then there are support servers that are only accessible “internally” to those web servers and not accessible from the outward facing public side of the network, i.e. Hadoop clusters, databases, etc.

To help log into the “internal” machines, I have pretty much one choice – using SSH through the public machine first. No problem here, any server admin knows how to use SSH – I’ve been using it forever. However, I didn’t really use some of the more advanced features that are very helpful. Here are two…

Remote command chaining

Most of my SSH usage is for running long sessions on a remote machine. But you can also pass a command as an argument and the results come directly back to your current terminal:

$ ssh user@host "ls /usr/lib"

Take this example one step further and you can actually inject another SSH command that gets into the “internal” side of the network.

This is starting to really sound like tunneling, though it’s somewhat manual and doesn’t redirect traffic from your client side, we’ll get to that later.

As an aside, in EC2-land you often use certificate files during SSH login, so you don’t need to have an interactive password exchange. You specify the certificate with another argument. If that’s how you run your servers (or with authorized_keys files) then you can push in multiple levels of additional SSH commands easily.

For example, here I log into ext-host1, then from there log into int-host2 and run a command:

$ ssh -i ~/mycert.pem user@ext-host1 "ssh -i ~/mycert.pem user@int-host2 'ls /usr/lib'"

That is a bit of a long line for just getting a file listing, but it’s easy to understand and gets the job done quickly. It also works great in shell scripts, in fact you could wrap it up with a simple script to make it shorter.

Proxy config

Another way to make your command shorter and simpler is to add some proxy rules to the ~/.ssh/config file. I didn’t even know this file existed, so was thrilled to find out how it can be used.

To talk about this, let’s use the external and internal hosts as examples. And let’s assume that the internal host is Obviously these don’t need to be specifically public or private SSH endpoints, but it serves its purpose for this discussion.

If we are typically accessing int-host2 via ext-host1 then we can setup a Proxy rule in the config file:

Host 10.0.*.*
ProxyCommand ssh -i ~/mycert.pem user@ext-host1 -W %h:%p

This rule watches for any requests on the 10.0… network and automatically pushes the requests through the ext-host1 as specified above. Furthermore, the -W option tells it to stream all output back to the same terminal you are using. (Minor point, but if you miss it you may go crazy trying to find out where your responses go.)

Now I can do a simple login request on the internal host and not even have to think about how to get there.

ssh -i ~/mycert.pem user@int-host2

I think that’s a really beautiful thing – hope it helps!

Another time I’ll have to write more about port forwarding…