Mac Tips: Mac OS X Remote Power Management

Mac OS X offers two different technologies for starting and stopping servers and for remote power management, including Wake on LAN (WoL) and the Lights Out Management (LOM) processor. Details on both follow.

A common goal in many multiple-system environments involves being able to either power up from a sleep state, or to power up from a complete powered-down state. The former operates from a low-powered sleep state, the latter requires hardware within the server that can keep the NIC and some related hardware and firmware processing powered up.

Wake on LAN

The former approach is common with various client systems, and is known by various names including Wake on LAN (WoL). In simplest terms, send a so-called Magic Packet at a sleeping Mac box, and the box should awaken and boot; booting from sleep state, rather than from a power-off state.

To enable WoL, the “Wake for Administrator Access” setting is available within the Power Saver settings on Mac OS X 10.5 Leopard release; awaken for network access.

Historically, WoL goes back as far as features of the Digital Equipment Corporation (DEC) DEQNA Q-bus Ethernet network interface controller (NIC) commonly used on the MicroVAX series systems that were available and common during the 1980s. If not from earlier NICs. See the TRIGGER command within the DECnet NCP utility for related details.

Xserve Lights Out Management (LOM)

The latter approach is a full cold-start from a powered-down server. Xserve is the only box around that (once configured) can inherently do a full cold-start remote power up; Xserve has a LOM module that's always on when the box is plugged in, and the LOM is something which is not present on most other boxes.

Xserve LOM is low-level hardware, firmware, and software. The LOM hardware is available as a feature of Xserve servers, and is presently not available in other Mac systems. LOM has limited remote access capabilities, as well.

Apple TA24506 describes the LOM hardware, and HT2773 describes the LOM configuration process.

The HP analog of the Xserve LOM is the server management processor (MP) known as the iLO or the iLO2, typically. ILO and ILO2 provide advanced remote management capabilities, including remote network terminal access into the console. Older management boards for some of the HP product lines are known as the RMC or RCM, depending on the hardware and hardware generation.

ACPI Power Details

Wake On LAN (WoL) can be ACPI state S5 within various HP clients and the HP console (BIOS) console, or within the Xserve LOM. Apple Mac client hardware typically implements an ACPI S4-level save, and then resides in ACPI S3 state until the power is disconnected; S2 state.

In the case of the HP hardware or the Mac client hardware, some chunk of the components of the box have to remain powered up; the power supply, the NIC and the firmware all certainly need to be active, regardless of whether WoL starts from the S3, S4 or S5 state.

No box can boot from S2 state without an external switch; without an external control over the power.

Options and Alternatives

Apple typically does not cater to the enterprise, and does not have the breadth of products and features of vendors including HP.

HP has various options unavailable within the Mac product line; if an ACPI S5 state is a prerequisite for an installation, then you'll be choosing a different client, or a network-capable power strip or network-capable Less Interruptible Power Supply (LIPS) widget. Whether the distinction among S3, S4, or S5 or the LOM or WoL matters is a local decision.

For other mechanisms and options, see the Mac OS X Hints Wake on LAN document, see Apple TA21254, and the Brandeis Wake on LAN for Mac OS X and via iPhone. Also available is the Mac OS X Server documentation, as well as documentation for specific Apple Mac hardware.

Comments

Bonjour Sleep Proxy

Here's Mac OS X v10.6: About Wake on Demand (HT3774); where the Airport or Time Capsule router can wake a sleeping Mac.