It's not shutdown, anycase take a look at the following command:
pm-action - Suspend or Hibernate your computer
pm-suspend [--quirk-*] [--help]
pm-suspend-hybrid [--quirk-*] [--help]
From man page:
These commands can be used to put the machine in a sleep state. The precise way how this
is done can be influenced by installing executables and configuration snippets. For some
options external programs are needed.
These commands will usually be called by UPower or hald when triggered to do so by a
program in a desktop session such as gnome-power-manager. Calling them from the command
line is also possible, but it is not guaranteed that all programs in your desktop session
keep working as expected.
During suspend most devices are shutdown, and system state is saved in RAM. The system
still requires power in this state. Most modern systems require 3 to 5 seconds to
enter and leave suspend, and most laptops can stay in suspend mode for 1 to 3 days
before exhausting their battery.
During hibernate the system is fully powered off, and system state is saved to disk.
The system does not require power, and can stay in hibernate mode indefinitely. Most
modern systems require 15 to 45 seconds to enter and leave hibernate, and entering and
leaving hibernate takes longer when you have more memory.
Hybrid-suspend is the process where the system does everything it needs to hibernate,
but suspends instead of shutting down. This means that your computer can wake up
quicker than for normal hibernation if you do not run out of power, and you can resume
even if you run out of power. s2both(8) is an hybrid-suspend implementation.