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Latest Updates: bsd

• SSH Client: Automatically Connect to a Servers’ Non-Standard Port

  10:18 on August 2, 2009 | 0 Comments Tweet This! | Digg This!
  Tags: bsd, linux (28), os x (24), tips (64)

  If you run an SSH server, or many SSH servers, then you may have set the SSH daemon to run on a non-standard port. SSH normally listens on port 22, but with the large amount of script/bot attacks now on this port, attempting random logins, changing it to something different is a quick way to stop the majority of these automated attacks.  I’ve detailed this in another post here.

  Once you’ve done this, though, you probably get bored with having to specify the port every time you connect by typing ssh -p 1234 hostname or scp -P 1234 hostname (where 1234 is the port SSH is running on hostname) – I know I do!

  You can get around this problem, by using the ~/.ssh/config file (config in the .ssh directory in your home directory).

  You can add multiple hosts to this file, along with their port, so you can simply ssh hostname and it’ll connect  using whatever port is set in that file.

  The entry you need to add is:

  Host host.example.org
    Port 1234

  Where host.example.org is the hostname you SSH too (if you SSH to an IP address, then this will need to be set here) and Port 1234 is the port number SSH is running on hostname.

  Once this is done, you’ll be able to:

  ssh host.example.org

  … and it’ll know that you need to connect on the port set in the file.

  You can add multiple hosts to this file, if you access multiple SSH servers:

  Host host.example.org
    Port 1234

  Host host2.example.com
    Port 4567

  Give it a try – it’s certainly saved me some time!

  You may also want to checkout another post on droptips.com with further options for the ~/.ssh/config file:  http://droptips.com/ssh-client-saving-server-configuration-alias-port-username

   

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• Quick command to check the status of a URL (Linux, BSD, OS X)

  22:54 on July 28, 2009 | 0 Comments Tweet This! | Digg This!
  Tags: bsd, linux (28), os x (24), tips (64)

  There may be times when you just want to do a quick check to see whether a web site is up, and/or what status message the web server is showing. This won’t actually show you if the page it served up is correct or not, purely the web server status code on whether or not it served something/anything/nothing!

  There are lots of status codes for web servers, and they are detailed here: http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html

  So, to be able to see the status message, and to check if a host is up or not, we can use the curl command.  curl is installed by default on OS X, but you may need to install it on your Linux distribution or BSD installation.

  So, to do a quick check from a command line:

  curl -Is http://droptips.com | head -n 1

  And you’ll get something back similar to:

  HTTP/1.1 200 OK

  Status code 200 is “OK”.

  HTTP/1.1 200 OK

  As another example, to show you how this will display different status codes, you’ll notice that if you visit: http://www.droptips.com you are redirected to http://droptips.com, purely because I prefer not to have www in the URL.  I do this by implementing a 301 (Permanently moved) from within Apache for any client going to http://www.droptips.com:

  $ curl -Is http://www.droptips.com | head -n 1

  HTTP/1.1 301 Moved Permanently

  As you can see, the web server returned a 301, and this is shown.

  curl can also take full URLs, so you can check whether or not a particular page/path is being served or not:

  curl -Is http://droptips.com/tag/tips/ | head -n1
  HTTP/1.1 200 OK

  So if you want to see if that new redirect is working, or just to see if your web server is up and serving requests, give curl a go!  This is just a basic overview of one thing you can do with curl - it’s a very flexible command, and can be used in a number of scenarios, some of which I will post about in the future.

   

• Command Help using Manual Pages (man) (OS X, Linux, BSD)

  20:42 on July 27, 2009 | 0 Comments Tweet This! | Digg This!
  Tags: bsd, linux (28), os x (24), tips (64)

  As you start using the command line, you’ll come across thousands of different commands, all with their own options and ways of taking options.  Every command is different, but help is on hand in the form of man pages.

  Manual Pages (or man page for short) are the documentation distributed with every command (or, at least, should be with every command) which tells you how a particular command works.

  From a Terminal in OS X, Linux, or BSD, you should have access to a command called man.  man is the reader for these man pages, and parses them nicely onto the screen for you.

  So, for example, if you wanted help with the mount command, you would simply do:

  man mount

  … and you would be presented with the manual page for mount.

  This is true of any command, and there should always be a manpage with the command. It’s good practice to do this as a developer, but you may find cases where people don’t.

  There are also various web sites which have html versions of these manpages, and you can normally find these on the Linux or BSD distribution’s site you are using, or the Apple site.  For the sake of this post, the three below are for Ubuntu, FreeBSD, and OS X.

  Ubuntu - http://manpages.ubuntu.com/

  FreeBSD – http://www.freebsd.org/cgi/man.cgi

  OS X – http://developer.apple.com/documentation/Darwin/Reference/ManPages/

  So the next time you need help with a particular command, do a quick man thecommand and hopefully, you’ll have all the help you need!