If you need to ask a question on the FreeBSD-questions mailing list then
https://www.FreeBSD.org/doc/en_US.ISO8859-1/articles/\
freebsd-questions/index.html
contains lots of useful advice to help you get the best results.
To quickly create an empty file, use "touch filename".
-- Dru
You can open up a new split-screen window in (n)vi with :N or :E and then
use ^w to switch between the two.
Need to find the location of a program? Use "locate program_name".
-- Dru
You can use the 'fetch' command to retrieve files over ftp, http or https.
fetch 
will download the beastie image from the FreeBSD web site.
To set a quota of 10 GB for the user named foo on a ZFS dataset, run the
following command:
# zfs set userquota@foo=10G pool/home/foo
The zfs userspace command can display the quota and current space usage:
# zfs userspace pool/home/foo
To unset a quota, assign "none" as the value.
-- Benedict Reuschling
You can search for documentation on a keyword by typing
apropos keyword
To see the MAC addresses of the NICs on your system, type
ifconfig -a
-- Dru
Want to know how much memory (in bytes) your machine has installed? Let
sysctl(8) tell you with the following command:
sysctl hw.realmem
The realmem value is memory before the kernel and modules are loaded, whereas
hw.physmem is what is left after they were loaded.
The number of active CPUs is displayed using this command:
sysctl hw.ncpu
-- Benedict Reuschling
To see the 10 largest files in a directory or on a UFS partition, use
du -h /partition_or_directory_name | sort -rh | head
-- Dru
To see how much disk space is left on your UFS partitions, use
df -h
-- Dru
If you accidentally end up inside vi, you can quit it by pressing Escape, colon
(:), q (q), bang (!) and pressing return.
If you want to get a sorted list of all services that are started when FreeBSD boots,
enter "service -e".
-- Lars Engels
To clear the screen, use "clear". To re-display your screen buffer, press
the scroll lock key and use your page up button. When you're finished,
press the scroll lock key again to get your prompt back.
-- Dru
"man tuning" gives some tips how to tune performance of your FreeBSD system.
-- David Scheidt
To set a custom ZFS property on the mypool pool, you need to provide it
using the "key1:key2=value" syntax, where the colon (:) is used as the
separator and identifier from the built-in ZFS properties:
# zfs set warranty:expires=2038-01-19 mypool
The custom property is applied to all datasets and can be queried like any
built-in properties using zfs get:
zfs get warranty:expires mypool
To reset the value of a custom property, use the inherit subcommand:
# zfs inherit warranty:expires mypool
Removing a custom property from a pool is done using the -r flag to the
"zfs inherit" command:
# zfs inherit -r warranty:expires mypool
-- Benedict Reuschling
If you `set watch = (0 any any)' in tcsh, you will be notified when
someone logs in or out of your system.
Want to run the same command again?
In many shells (e.g., tcsh, zsh, bash) you can type "!!".
Can't remember if you've installed a certain port or not? Try "pkg info
-x port_name".
To see the 10 largest files in a directory or on a UFS partition, use
du -h /partition_or_directory_name | sort -rh | head
-- Dru