change log level & enable sysrq

echo 9 > /proc/sysrq-trigger

echo 1 >  /proc/sys/kernel/sysrq

alt + sysrq  +  p :  show cpu info

alt + sysrq  + t : show current task list

alt  + sysrq  + m : show memory info

redirect output from serial port

1. modify bios:

   (1)Change BIOS settings /Server/Serial Console Features/BIOS Redirection Port to

       [Serial port 1 or 2]

   (2)change direct to modem 

2.  modify /boot/grub/menu.lst for suse

     modify /boot/grub/grub.conf  for red hat

    console=ttyS0, 115200,vt100

3. modify /ect/inittab

    c0:2345:respawn:/sbin/agetty ttyS0 19200 vt100    

4. modify  /etc/securetty

    ttyS0

How to Scan new LUNs on Linux with QLogic driver

http://bash.cyberciti.biz/diskadmin/rescan-linux-scsi-bus/

line number

nl: number lines

cpu info

cat /proc/cpuinfo

interrupt context

1. can not relinquish cpu by calling sleep functions

GFP_KERNEL

allocate memory:

1. GFP_KERNEL:

    kmalloc() is allowed to go to sleep and wait for pages to get freed up.

2.GFP_ATOMIC:

   Used by interrupt context code to get hold of memory. In this mode, kmalloc() is not allowed to    sleep-wait for free pages, so the probability of successful allocation with GFP_ATOMIC is lower    than with GFP_KERNEL.