Snort is included with SuSE but not Red Hat. If you need it (or you want to upgrade), download the source distribution from http://www.snort.org and unpack it:

$ tar xvpzf snort-*.tar.gz

Then compile it:

$ cd `ls -d snort-* | head -1`
$ ./configure
$ make

and install the binary and manpage as root:

# make install

Next, create a logging directory. It should not be publicly readable, since it will contain potentially sensitive data:

# mkdir -p -m go-rwx /var/log/snort

Finally, install the configuration files and rules database:

# mkdir -p /usr/local/share/rules
# cp etc/* rules/*.rules /usr/local/share/rules