Tainted kernels:

Some oops reports contain the string 'Tainted: ' after the program
counter, this indicates that the kernel has been tainted by some
mechanism.  The string is followed by a series of position sensitive
characters, each representing a particular tainted value.

  1: 'G' if all modules loaded have a GPL or compatible license, 'P' if
     any proprietary module has been loaded.  Modules without a
     MODULE_LICENSE or with a MODULE_LICENSE that is not recognised by
     insmod as GPL compatible are assumed to be proprietary.

  2: 'F' if any module was force loaded by insmod -f, ' ' if all
     modules were loaded normally.

The primary reason for the 'Tainted: ' string is to tell kernel
debuggers if this is a clean kernel or if anything unusual has
occurred.  Tainting is permanent, even if an offending module is
unloading the tainted value remains to indicate that the kernel is not
trustworthy.


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from /usr/src/Lnx/linux-2.4.17/Documentation/oops-tracing.txt

