The uname command writes to standard output the name of the operating system that you are using.

# Print all system information
uname -a
# Linux system-hostname 3.2.0-4-amd64 #1 SMP Debian 3.2.32-1 x86_64 GNU/Linux

# Print the hostname
uname -n
# system-hostname

# Print the kernel release
uname -r
# 3.2.0-4-amd64

# Print the kernel version, with more specific information
uname -v
# #1 SMP Debian 3.2.32-1

# Print the hardware instruction set
uname -m
# x86_64

# Print the kernel name
uname -s
# Linux

# Print the operating system
uname -o
# GNU/Linux