'Dedicated administrator connections are not supported. (ObjectExplorer)' error

Dedicated Administrator Connection (DAC) is a new feature of SQL Server 2005; it is a special diagnostic connection for administrators that can be used to connect to a server when standard connections are not possible.

If you are trying to connect to a server using the DAC with SQL Server Management Studio and you keep getting the following error:

Dedicated administrator connections are not supported. (ObjectExplorer)

it means that you are trying to connect Object Explorer using the DAC.

Object Explorer cannot connect using the DAC; only Query Window can. That means that you cannot press the New Query button; you have to use the Database Engine Query button.

HOWTO: Calculate MD5 checksum in Windows (and other checksums, too)

On Linux that's trivial - there is the md5sum program.

Windows does not come with such a tool, but you can use md5deep package.

md5deep is a cross-platform set of programs to compute MD5, SHA-1, SHA-256 Tiger, or Whirlpool message digests on an arbitrary number of files. The programs run on Windows, Linux, Cygwin, *BSD, OS X, Solaris, and should run on most other platforms. md5deep is similar to the md5sum program found in the GNU Coreutils package (...)

HOWTO: Perform a scheduled shutdown without installing additional software

The easiest way of performing a scheduled shutdown of a Linux computer, that came to my mind, was executing something like this:

  sleep 3600 && poweroff

However, this couldn't work, since root privileges are necessary to run poweroff command. So you have to use:

  sleep 3600 && sudo poweroff

But this will cause the computer to wait for 1 hour (3600 seconds) and then prompt for the root password. And what we are trying to avoid is sitting in front of the computer at that time.

But there is a very simple solution:

1. Type sudo visudo to edit the /etc/sudoers file.
2. Add the following line:

    your_username ALL= NOPASSWD: /sbin/poweroff

Now you can execute sudo poweroff without typing the password.

ISNULL, implicit conversion and integer data type

SELECT ISNULL(CAST(NULL as int), '+')
0

SELECT ISNULL(CAST(NULL as int), '-')
0

SELECT ISNULL(CAST(NULL as int), '/')
Server: Msg 245, Level 16, State 1, Line 1
Conversion failed when converting the varchar value '/' to data type int.

To explain the above one must to remember that:

1. ISNULL returns the same type as the check expression (that's the 1st parameter),
2. varchar and char data types can be implicitly converted to int (if you don't know what it means, try executing SELECT 2 + '2'),
3. SQL Server treats '+' and '-' characters as a number - 0.

So this is what happens - ISNULL tries to return int data type and it converts the replacement value (that's the 2nd parameter); it succeeds in 2 cases, but fails in the 3rd one, because '/' is not a numeric expression.

Linux applications - languages

If a Linux application starts and the interface is translated into some language that you don't want to use (or even worse - it is partly translated, as it was in my case, so names in the menus were a mix of English and Polish words), you can go to:

/usr/share/locale/[language_folder]

and delete [application_name].mo file.

Rather a dirty hack, but it works.

You will need root privileges, of course.