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Sending a single packet and waiting for a response is going to be one of the fastest possible ways, and ping is a fine way to do that. In fact, depending on your use case, I'd argue that it's too fast, since it doesn't really tell you if the system is actually doing anything useful, just that the kernel's network subsystem is alive and configured. But ...

I have had luck using PowerNap (it is packaged for ubuntu-sever, but the source is there so you should be able to compile it on anything) to suspend backup machines when they aren't doing anything. However, this won't wake them up automatically. There is also a PowerWake program bundled with the PowerNap source tarball (packaged as powerwake in Ubuntu) ...

OS X can do this now, as of Snow Leopard. It's made possible through the Sleep Proxy Service. It's pretty much automatic. The only requirement is that you have a second always-on Apple device on your LAN that can act as the sleep proxy. Their current low-power embedded boxes all support this, I believe: Airport, Time Machine, and Apple TV. In the ...

You need something that's capable of sending an Ethernet packet that will be seen by the device you want to wake up. The ether-wake command in BusyBox is exactly what you're after. If your BusyBox doesn't have it, consider recompiling BusyBox to include it. If you have a sufficiently “bloaty” netcat (BusyBox can have one of two nc implementations, one of ...

What you could do it ping the broadcast address which should cause all the computers to ping back. Then you could cross check this list against what you have in SQLite to ensure all the computers are up. Other then that a ping is probably the fastest way to ensure a computer is awake on a network. As mentioned by the other answer this doesn't provide any ...

Wake on LAN is a BIOS and NIC feature, not an OS feature, that is, you need a supporting BIOS and NIC to do it. Once you've enabled it in your BIOS (if you can), you can check if your NIC has WOL support enabled by checking the output of ethtool [interface]. If the value of Supports Wake-on contains g, your NIC supports WOL magic packets. To check if it ...

Here are a couple of easy ways for your server to check if other devices are using it: Check the arp cache using /usr/sbin/arp or by reading /proc/net/arp. You'll see in there all the devices which the server has communicated with fairly recently. This includes the MAC address, so you can find your phone, etc. even in the face of DHCP. Use ping (or arping, ...

/dev/udp is recognized by bash and doesn't really exist in the filesystem, so give it a try. I think you can use syslogd without -l switch, as long as it supports -R. I have busybox with syslogd withount -R, no nc nor bash and I'm still stuck.