How to Enable or Disable a processor in Sun Solaris

In multiprocessor environments, Sun Solaris can allow enabling or
disabling Processors. This although is not something that we would do
all the time but can come handy when troubleshooting hardware issues.

Sun
Solaris has the psradm utility which allows enabling or disabling a
Processor on the system. The psradm utility changes the operational
status of processors. The legal states for the processor are on-line,
offline, spare, Faulted, and no-intr. An online processor processes
LWPs (lightweight  processes) and can be interrupted by I/O devices in
the system.

To enable or disable
a processor on the system we need to know the Processor ID. This can be
found using the psrinfo utility as follows:

sunsolaris# psrinfo
0       on-line   since 05/09/2008 19:41:32

where 0 is the processor ID.

To know the path of the psradm command

sunsolaris# which psradm
/usr/sbin/psradm

To disable a processor

sunsolaris# psradm -f 0

where ‘0′ is the processor ID and ‘-f’ indicates the processor is taken offline (disable)

To enable a processor

sunsolaris# psradm -n 0

where ‘0′ is the processor ID and ‘-n’ indicates the processor is brought online (enable)

Source: http://www.sunsolarisadmin.com/hardware/how-to-enable-or-disable-a-processor-in-sun-solaris/#more-57