Configure a port adding or removing options before installing.

make WITHOUT="IPV6" WITH="RSS_DIFF SSL"
make install clean

Configure a port adding or removing options including dependencies before installing.

make config-recursive
make install clean

Install a port and automatically select YES to all questions.

make install clean BATCH=yes

Show compiled options.

make showconfig

Remove current port configuration prior to installation.

make rmconfig

Remove current port configuration recursive prior to installation.

make rmconfig-recursive

echo 'OPTIONS_UNSET=IPV6' >> /etc/make.conf

mkdir /cdrom
mount -t cd9660 /dev/cd0 /cdrom

FreeBSD does not have an md5sum command install it like this.

cd /usr/ports/sysutils/coreutils && make install clean

Then use the command like this.

/usr/local/bin/gmd5sum filename

interface_name equals your network card name i.e em0 eth0 wlan0.

/etc/rc.d/netif restart em0

cd into the directory where you get the error then run

ls | xargs rm -fR