try this:
cat /etc/issue

or run this:
#!/bin/sh
# Detects which OS and if it is Linux then it will detect which Linux Distribution.

OS=`uname -s`
REV=`uname -r`
MACH=`uname -m`

GetVersionFromFile()
{
	VERSION=`cat $1 | tr "\n" ' ' | sed s/.*VERSION.*=\ // `
}

if [ "${OS}" = "SunOS" ] ; then
	OS=Solaris
	ARCH=`uname -p`	
	OSSTR="${OS} ${REV}(${ARCH} `uname -v`)"
elif [ "${OS}" = "AIX" ] ; then
	OSSTR="${OS} `oslevel` (`oslevel -r`)"
elif [ "${OS}" = "Linux" ] ; then
	KERNEL=`uname -r`
	if [ -f /etc/redhat-release ] ; then
		DIST='RedHat'
		PSUEDONAME=`cat /etc/redhat-release | sed s/.*\(// | sed s/\)//`
		REV=`cat /etc/redhat-release | sed s/.*release\ // | sed s/\ .*//`
	elif [ -f /etc/SuSE-release ] ; then
		DIST=`cat /etc/SuSE-release | tr "\n" ' '| sed s/VERSION.*//`
		REV=`cat /etc/SuSE-release | tr "\n" ' ' | sed s/.*=\ //`
	elif [ -f /etc/mandrake-release ] ; then
		DIST='Mandrake'
		PSUEDONAME=`cat /etc/mandrake-release | sed s/.*\(// | sed s/\)//`
		REV=`cat /etc/mandrake-release | sed s/.*release\ // | sed s/\ .*//`
	elif [ -f /etc/debian_version ] ; then
		DIST="Debian `cat /etc/debian_version`"
		REV=""

	fi
	if [ -f /etc/UnitedLinux-release ] ; then
		DIST="${DIST}[`cat /etc/UnitedLinux-release | tr "\n" ' ' | sed s/VERSION.*//`]"
	fi
	
	OSSTR="${OS} ${DIST} ${REV}(${PSUEDONAME} ${KERNEL} ${MACH})"

fi


echo ${OSSTR}

#!/bin/sh
# Detects which OS and if it is Linux then it will detect which Linux Distribution.

OS=`uname -s`
REV=`uname -r`
MACH=`uname -m`

GetVersionFromFile()
{
	VERSION=`cat $1 | tr "\n" ' ' | sed s/.*VERSION.*=\ // `
}

if [ "${OS}" = "SunOS" ] ; then
	OS=Solaris
	ARCH=`uname -p`	
	OSSTR="${OS} ${REV}(${ARCH} `uname -v`)"
elif [ "${OS}" = "AIX" ] ; then
	OSSTR="${OS} `oslevel` (`oslevel -r`)"
elif [ "${OS}" = "Linux" ] ; then
	KERNEL=`uname -r`
	if [ -f /etc/redhat-release ] ; then
		DIST='RedHat'
		PSUEDONAME=`cat /etc/redhat-release | sed s/.*\(// | sed s/\)//`
		REV=`cat /etc/redhat-release | sed s/.*release\ // | sed s/\ .*//`
	elif [ -f /etc/SuSE-release ] ; then
		DIST=`cat /etc/SuSE-release | tr "\n" ' '| sed s/VERSION.*//`
		REV=`cat /etc/SuSE-release | tr "\n" ' ' | sed s/.*=\ //`
	elif [ -f /etc/mandrake-release ] ; then
		DIST='Mandrake'
		PSUEDONAME=`cat /etc/mandrake-release | sed s/.*\(// | sed s/\)//`
		REV=`cat /etc/mandrake-release | sed s/.*release\ // | sed s/\ .*//`
	elif [ -f /etc/debian_version ] ; then
		DIST="Debian `cat /etc/debian_version`"
		REV=""

	fi
	if [ -f /etc/UnitedLinux-release ] ; then
		DIST="${DIST}[`cat /etc/UnitedLinux-release | tr "\n" ' ' | sed s/VERSION.*//`]"
	fi
	
	OSSTR="${OS} ${DIST} ${REV}(${PSUEDONAME} ${KERNEL} ${MACH})"

fi


echo ${OSSTR}

From http://www.novell.com/coolsolutions/feature/11251.html

What linux distro is this?

linux

Bash