6 On Sun Systems And Break

Anyone who has turned off a terminal used as a console for a Sun system will know what happens and why this is a problem. Sun hardware recognises a serial BREAK as a command to halt the OS and return to the ROM monitor prompt. A serial BREAK is an out-of-band signal on an RS-232 serial port that involves making the TX DATA line active (i.e. pulled down to less than -5v) for more than two whole character times (or about 2ms on a 9600bps line). Alas, this BREAK signal is all to easily generated by serial hardware during power-on or power-off. And the Stallion card does, in fact, generate breaks when the power to the PC fails. Unless fixed, this problem would mean that every Sun box connected to the console server would be halted whenever the power failed (due to dead power supplies, or fat-fingered operators unplugging it, or whatever). This is clearly not an acceptable situation.

Fortunately, Sun have come up with a set of fixes for this. For Solaris™ 2.6 and later, the kbd(1) command can be used to disable the ROM-on-BREAK behaviour. This is a good start, but leaves you out of luck in the situation where a break is needed to get into a broken machine.

Starting with Solaris 8, the kbd command can also be used to enable an alternate break sequence using the kbd -a alternate command. When this is set, the key sequence ReturnTildeCtrl-B (within 5 seconds) will drop to the ROM. You can enable this permanently by editing the /etc/default/kbd file; see the kbd(1) man page. Note that this alternate break sequence is only active once the kernel has started running multiuser and processed the default file. While the ROM is active (during power-on and during the boot process) and while running single-user, you still need to use a BREAK to get to the ROM prompt. The console client can cause the server to send a BREAK using the escape sequence Esccl1.

If you have a Sun software support contract, there are patches available for Solaris 2.6 and 2.7 that add the “alternate break” capability integrated into Solaris 2.8. Solaris 2.6 requires patch 105924-10 or higher. Solaris 2.7 requires patch 107589-02 or higher.

We have added this patch to all our Solaris 2.6 servers, and added it (and the entry in the /etc/default/kbd file) to our jumpstart configuration so it will automatically be added to every new install.

We have confirmed by direct testing that neither the Cisco 16xx, 26xx, or Catalyst® hardware suffers from the BREAK sent when the Stallion card loses power. Contemporary Cisco software listens for BREAK signal only for first 30 seconds after power-on or reboot.