System Monitoring in linux

File containing Boot messages:
/var/log/boot.msg

To view the content of current kernel buffer:
# dmesg

Few /proc files containing system info:

/proc/cpuinfo : View processor information
/proc/meminfo : View memory information
/proc/devices : View the devices configured on your linux machine
/pro/ioports : View the I/O ports
/pro/interrupts : View the IRQ assignments
/proc/dma : View the DMA channels
/proc/bus/pci/devices : View the PCI information
/proc/scsi/scsi : View the scsi information

Fiew Commands to view hardware details:

To display the list of hardware(devices) installed in your system:
# hwinfo

To display hard drive info and manage its paramets:
# hdparm

To list the current disk partitions:
# fdisk

To display the CPU and I/O statistics:
# iostat

To display the list of PCI buses and the devices connected to it:
# lspci

To collect the system information in HTML or ASCII format:
# siga

To prepare system information using Perl:
# sitar

To display the current time, system uptime, # of users on the system:
# uptime

To list the network ports and their offered services:
# netstat -patune

To display current kernel version:
# uname -a

To display the cpu, memory, swap usage :
# top

To display the system memory and swap usage:
# free

To display memory, swap, io, system and cpu usage:
# vmstat

To display the kernel type:
# getconf LONG_BIT