Is There A Network Equivalent Of Alt-SysReq?

Random Q. Hacker asks: "Alt-SysReq has saved me from filesystem damage and runaway processes more than once. Unfortunately, several of the machines I admin are thousands of miles away in data centers, and it takes 15 minutes for data center personnel to go to our cage, hook up a monitor to the right system, and call back for interactive troubleshooting. I have played with snmpd, but it's a userspace daemon, and most of its functionality involves executing external programs and accessing files. Sometimes a system gets hung so bad (say, on root becoming unavailable, or memory becoming completely full) that the only thing still working is the kernel itself. Is there a kernel backdoor (as in a patch) that could let me have (secure, authenticated) SysReq functionality through the network?"

Comments

Re:I never knew what SysReq did anyway.

[coyote-san]

The easiest way to answer this is to compare it to the "break" signal on serial ports, or the hook "flash" on telephones. The SysReq key is (or is supposed to be) an equivalent "out of band" signal from the keyboard and should always be recognized even if the keyboard buffer is full, hosed, or otherwise unusable.

What do you do with "SysReq"? Anything you want. On some systems, particularly in a "secure" environment, the "SysReq" key is how you get a login prompt because it is how you can ensure that you're seeing the real login program, not a password sniffing userspace front-end. That's the thinking behind WinNT using "Ctl-Alt-Del" to bring up the login screen.

On Linux, the kernel can be configured to bring up a very small "monitor" that allows you to perform a few tasks (e.g., sync'ing the hard disks and performing a clean shutdown) when all else fails.

I don't believe any handlers are installed for Windows non-NT or DOS.