/proc/version - kernel version

/proc/version This string identifies the kernel version that is currently running. It includes the contents of /proc/sys/kernel/ostype, /proc/sys/kernel/osrelease, and /proc/sys/kernel/version. For example:

Linux version 1.0.9 (quinlan@phaze) #1 Sat May 14 01:51:54 EDT 1994

proc(5)