Linux Administration - Kernel information

Files 

pre-2.6.x 
2.5.9 (3 digits)
first number - major release
second number - even (stable kernel), odd (development kernel)
third number - minor upgrade 

2.6.x and later
2.6.11.10 (4 digits)
first number - major release
second number - minor patches
third number - significant changes made by Linus Torvalds
forth number - trivial changes

Commands 
uname [-a --all]
Display all the kernel information.

uname [-i --hardware-platform]
Display the hardware platform.

uname [--help]
Display usage information for uname.

uname [-m --machine]
Display the machine architecture code.

uname [-n --nodename]
Display network hostname.

uname [-o --operating-system]
Display the OS information.

uname [-p --processor]
Display the machine cpu description.

uname [-r --kernel-release]
Display the kernel release number.

uname [-s --kernel-name]
Display the name of the kernel. (normally Linux)

uname [-v --kernel-version]
Display the kernel build date and time.

uname [--version]
Display the version of uname.