Shutdown Totally Explained

Everything about Shutdown totally explained

Shutdown can be used to mean "turning off" something, but most commonly used for machines or industrial plants such as computers, engines, nuclear reactors, petroleum refineries, fossil fuel power plants, and petrochemical plants. It also has a use in economics, for profit maximization.

Nuclear reactors

In a nuclear reactor, shutdown refers to the state of the reactor when it's subcritical by at least a margin defined in the reactor's technical specifications. Further requirements for being shut down may include having the reactor control key be secured and having no fuel movements or control systems maintenance in progress.
The shutdown margin is defined in terms of reactivity, frequently in units of delta-k/k (where k is taken to mean k-effective,web the effective multiplication factor) or occasionally in dollars. Shutdown margin refers to the margin by which the reactor is subcritical when all control rods are in OR the margin by which the reactor would be shut down in the event of a scram. Hence, care must be taken to define shutdown margin in the most conservative way in the reactor's technical specifications; a typical research reactor will specify the margin when in the cold condition, without xenon. Under this specification, the shutdown margin can be simply calculated as the sum of the control rod worths minus the core excess.
Minimum shutdown margin can be calculated in the same way as shutdown margin, except that the negative reactivity of the most reactive control rod is ignored. This definition allows the reactor to be designed so that it remains safely shut down even if that most reactive control rod becomes stuck out of the core. See also: scram

Computers

In Unix, the shutdown command can be used to turn off or reboot a computer.
   One commonly issued form of this command is shutdown -h now, which will shut down a system immediately. Another one is shutdown -r now to reboot. Another form allows the user to specify an exact time or a delay before shutdown: shutdown -h 20:00 will turn the computer off at 8:00 PM, and shutdown -r -t 60 will automatically reboot the machine within 60 seconds (one minute) of issuing the command.
   The complete syntax of the Linux version of the command is:
usage: shutdown [-akrhfnc] [-tsecs] time [message] -a use /etc/shutdown.allow -k don't really shutdown, only warn -r reboot after shutdown -h halt after shutdown -f do a 'fast' reboot (skip fsck) -F force fsck on reboot -n don't go through "init" but go down real fast -c cancel a running shutdown -t secs delay between warning and kill signal
   Generally you must be the superuser (usually root) to shut the system down. This prevents unprivileged users (for example, schoolchildren) from causing potentially catastrophic damage to a server.
   In Mac OS X the computer can be shut down by choosing "Shut Down…" from the Apple Menu or by pressing the power key to bring up the power management dialog box. An administrator may also use the Unix shutdown command as well.
In Microsoft Windows, a PC or server is shut down by selecting the Shutdown item from the Start menu on the desktop. Options include shutting down the system and powering off, automatically restarting the system after shutting down, or putting the system into stand-by mode. There is also a shutdown command that can be executed within a command shell window. ==

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