i have S2600CP2 server board
this is operating in a custom chassis with 9 cooling fan with pwm control pin ( STS200C CPU cooler 2ea / system fan 6ea / rear fan 1ea)
can i control the fan speed through ipmitool or anything, without change the pwm offset value in bios?
As the fan control is handled by the Baseboard Management Controller automatically,the closest to your request is Advanced/System Acoustic and Peformance Configuration section within the BIOS:
Besides, I checked into the System Configuration utility (syscfg) Utility (click here for its download), but did not find any instructions as to how to manually change the fan speed through any of its commands.