Switching to runlevel 'S' appears to cause server hang

This document (7006930) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 11

Situation

Switching to runlevel 'S' (either from another runlevel, or during server startup) causes the server to appear to hang while starting microcode.ctl. At this same time, the following messages are seen on the console:

microcode: CPu0 sig=0x6fb, pf=0x40, revision=0xb7
platform microcode: firmware: requesting intel-ucode/06-0f-0b

If enough time is given, the server will actually continue to boot. However, there is a delay of 60 seconds per CPU core during this microcode firmware update. This causes the appearance of a server hang.

Resolution

The cause of this hang is the microcode firmware update which is being initiated from microcode.ctl. This update fails in runlevel 'S' due to the boot.udev and sysfs not being available in this runlevel.

To resolve this issue, disable microcode.ctl in runlevel S through the following steps:

1. Edit /etc/init.d/microcode.ctl and remove the 'S' runlevel from Default-Start. In other words, change:
        # Default-Start:     1 2 3 5 S
    to
        # Default-Start:     1 2 3 5

2. Remove and re-add microcode.ctl to system startup using:
       insserv -r microcode.ctl
       insserv microcode.ctl

The above changes will be the default configuration in newer versions of the microcode startup script.

Disclaimer

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