How do I set shutters speeds slower than 1/30 on canon 5d markII ? In the manual setting I cannot seem to scroll down slower than 1/30.
If the top of camera LCD display and viewfinder are showing [30"] (without the brackets) the selected shutter speed is 30 seconds which is the same as one-half minute. For shutter speeds slower than 30 seconds you will need to use Bulb mode (B on the Mode Dial) and time the shot with a watch or use a cable release with a built in timer.
If the display in the viewfinder and top of camera LCD is showing  (without the brackets) the selected shutter speed is 1/30 second.
On quick way to double check is to use the Quick Control screen. While shooting in M or Tv mode press the small, 8-way button at the top right of the LCD screen on the back of the camera straight down. The Quick control screen will appear on the LCD and the selected shutter speed (Tv) will be displayed in the upper left corner. If you have selected a speed of 1/4 second or shorter the Tv will be displayed as a fraction [1/30]. For shutter speeds between 1/4 and 1 second the display will show [0"] followed by a number denoting tenths of seconds. So [0"3] is 3/10 seconds, [0"4] is 4/10 seconds, and so on. If you have selected a shutter time of one second or longer, the number of seconds followed by ["] and then tenths of seconds, if any, will be displayed [30"]
Another way to see the Quick Control Screen is to use the Custom Functions to map the SET button to turn on the Quick Control Screen. Set C. Fn IV:3 (Assign SET Button) to option 5: Quick Control screen. When in normal shooting mode press the Set button in the middle of the large control dial on the back of the camera to turn on the Quick Control Screen.
Select B on the mode dial, not M. The 5DMkII has an explicit bulb mode setting, so you don't have to scroll past 30" to get to bulb mode. In Bulb mode, you can then hold down the shutter button for the duration of shutter speed you want, or use a cable release with a lock. The top LCD panel displays a count of the seconds that the shutter is open.