Editing Wake-on-LAN (section)

==Other machine states and LAN wakeup signals==
In the early days of Wake-on-LAN the situation was relatively simple: a machine was connected to power but switched off, and it was arranged that a special packet be sent to switch the machine on.

Since then many options have been added and standards agreed upon. A machine can be in seven [[Advanced Configuration and Power Interface#Power states|power states]] from S0 (fully on) through S5 (powered down but plugged in) and disconnected from power (G3, Mechanical Off), with names such as "sleep", "standby", and "hibernate". In some reduced-power modes the system state is stored in RAM and the machine can wake up very quickly; in others the state is saved to disk and the motherboard powered down, taking at least several seconds to wake up. The machine can be awakened from a reduced-power state by a variety of signals.

The machine's BIOS/UEFI must be set to allow Wake-on-LAN. To allow wakeup from powered-down state S5, wakeup on PME (Power Management Event) is also required. The Intel adapter allows "Wake on Directed Packet", "Wake on Magic Packet", "Wake on Magic Packet from power off state", and "Wake on Link".<ref>{{cite web |url= https://cs.uwaterloo.ca/~brecht/servers/docs/PowerEdge-2600/en/IntelNIC/wol.htm |title=Remote Wake-Up: Intel® Network Adapters User Guide |first=Tim |last=Brecht |work=[[University of Waterloo]] |year=2003 |access-date=28 October 2015}}</ref> Wake on Directed Packet is particularly useful as the machine will automatically come out of standby or hibernation when it is referenced, without the user or application needing to explicitly send a magic packet. Unfortunately in many networks waking on directed packet (any packet with the adapter's MAC address or IP address) or on link is likely to cause wakeup immediately after going to a low-power state. Details for any particular motherboard and network adapter are to be found in the relevant manuals; there is no general method. Knowledge of signals on the network may also be needed to prevent spurious wakening.

===Waking up without operator presence===

If a machine that is not designed to support Wake-on-LAN is left powered down after power failure, it may be possible to set the BIOS/UEFI to start it up automatically on restoration of power, so that it is never left in an unresponsive state. A typical BIOS/UEFI setting is ''AC back function'' which may be ''on'', ''off'', or ''memory''. ''On'' is the correct setting in this case; ''memory'', which restores the machine to the state it was in when power was lost, may leave a machine which was hibernating in an unwakeable state.

Other problems can affect the ability to start or control the machine remotely: hardware failure of the machine or network, failure of the BIOS/UEFI settings battery (the machine will halt when started before the network connection is made, displaying an error message and requiring a keypress), loss of control of the machine due to software problems (machine hang, termination of remote control or networking software, etc.), and virus infection or hard disk corruption. Therefore, the use of a reliable server-class machine with [[RAID]] drives, redundant power supplies, etc., will help to maximize availability. Additionally, a device which can switch the machine off and on again, controlled perhaps by a remote signal, can force a reboot which will clear problems due to misbehaving software.

For a machine not in constant use, energy can be conserved by putting the machine into low-power RAM standby after a short timeout period. If a connection delay of a minute or two is acceptable, the machine can timeout into hibernation, powered off with its state saved to disk.