Monday 15 June 2009
Part 2: Monitoring SSH status in Mac OS X Terminal
Friday 12 June 2009
Part 1: Monitoring AFP Status in Mac OS X Terminal
- The first is GeekTool which I've only come across recently. It's a great way to run multiple terminal commands which overlay on top of your desktop, which when you're playing around in unix is a useful way to monitor the output of various commands without continuously having to retype them.
- The second is CLIX a useful 'teaching aid' for unix on Mac OS X. I learnt some useful tail and cut commands from CLIX to get just the output from the terminal that I was looking for.
Proto Recv-Q Send-Q Local Address Foreign Address
tcp4 0 0 *.afpovertcp *.* LISTEN
tcp6 0 0 *.afpovert *.* LISTEN
Netstat is telling us that there is a server process LISTEN-ing for remote connections from any address (*.*) that want to connect to a service running on the local machine called afpovertcp (afp-over-tcp).
Disable Apple File Sharing in System Preferences and run Netstat again. This line disappears i.e. the computer is no longer listening for incoming AFP connections.
Great! so netstat tells us whether or not AFP is enabled in System Preferences. But I don't want to navigate through the verbose output of nestat each time to view this. Fortunately, there are various unix commands to help us limit the output of netstat to just what we are looking for.
First, we can limit the output of nestat and speed up it's response by limiting the results it returns to look at one particular address family, in this case we can use inet6:
netstat -a -f inet6
Try it! Secondly we can 'pipe' the output of netstat through grep - to limit the output to the exact line that we are looking for:
netstat -a -f inet6 | grep afpovert
This command firstly runs netstat -a -f inet6 but only returns the lines which include the text afpovert. i.e. grep is acting like a filter to return only the lines we are interested in. Here's the result:
tcp6 0 0 *.afpovert *.* LISTEN
However, the response time is still slower that what I'd like as netstat is still having to run a command to investigate all network connections on the inet6 family of addresses, before it returns its result subsequently filtered by grep. If you're running Tiger, you'll see what I mean.
If we look at the options of netstat:
man nestat
We find we can add the -n option to only show us port numbers rather than an interpreted symbolic address i.e. if we know what port number AFP is running on, we can look for this in netstat's output, rather than asking netstat to do extra work of displaying the symbolic address of all connections. Fortunately, AFP consistently runs on port 548 so we can change our command to:
netstat -naf inet6 | grep 548
Great! an instant result:
tcp6 0 0 *.548 *.* LISTEN
So if I run this command and it returns a result, then I know that AFP is enabled in my System Preferences. Or do I?
Actually, my grep command isn't sophisticated enough. What if there is a different service running on port 5482? or 1548? or any combination of numbers which includes the pattern 548? We will then return an incorrect result as to whether file sharing is enabled or not. We need to improve our grep filter to match exactly what we are looking for in netstat's result.
Lets first ensure we include the *. before the 548 so no numbers can preceed the actual port value we are looking for:
netstat -naf inet6 | grep [*][.]548
As * and . are special characters as part of regular expressions, we need to surround them each with a [ square brace ]. Finally we want to ensure there is a blank space character after 548. To do this, we need to use an escape character \ and a space surrounded by square braces to ensure we force grep to pattern match exactly the number we are looking for. Our expression then becomes:
netstat -naf inet6 | grep [*][.]548[\ ]
For good measure, lets also ask grep to also only return results from netstat of connections which are actively listening for connections, as the AFP service should do:
netstat -naf inet6 | grep [*][.]548[\ ].*LIST
The . after the square brace means 'concatenate' or add the next thing that comes to the query. The following * effectively means: any number of characters inbetween the end of the space character we've just looked for until the next pattern. LIST is for LISTEN in order to remove pattern matching of other connections from the list e.g. ESTABLISHED etc...
So here we have our command for checking if AFP is enabled:
netstat -naf inet6 | grep [*][.]548[\ ].*LIST
phew!
Tuesday 9 June 2009
Preview: Who Is Connected?
Monitoring SSH & AFP Status for Mac OS X
I've always wanted to glance up into the menu bar and see the status of Apple File Sharing (AFP) and Remote Login (SSH) on my Mac. Apple provide a whole range of menu bar (NSStatus) options for AirPort, bluetooth, sound, date, time, battery life etc... But not for file sharing.
In fact, not only would I like to see what's happening in relation to File Sharing and SSH connections, I'd like to be notified of new connections. Having to jump into System Preferences in order to view current sharing status and monitor netstat via terminal to review current connections, seems a little too labour intensive for such a simple request.
After extensive Googling, I was surprised that I couldn't find any ready made solutions. The best I could find was AFPStatus over at sparrer-online.de, however, I wanted something with a smaller footprint, a simpler icon and additional functionality of monitoring incoming SSH connections.
After playing around with AppleScript and the excellent Growl notification framework, I quickly had a working version of a simple notification application which highlighted new incoming SSH connections. So how big would the step be to get this working as a true app for Mac OS X?
Having wanted to for a while, I had finally found an excuse to take the plunge and dive into Xcode. So over the next few blogs, I'll run through my journey of creating Version 1.0 of Who Is Connected? due for release June 09.
>> Part 1: Monitoring AFP Status in Mac OS X Terminal