How do I enable or disable an apache virtual host?

To enable an apache virtual host run the following command:

sudo a2ensite example.com

To disable an apache virtual host run the following command:

sudo a2dissite example.com

Both of the examples above assume you're interested in enabling/disabling the site configured via the following file:

/etc/apache2/sites-available/example.com

Lastly, if you're interested in learning more about the a2ensite/a2dissite command, checkout the following notes:

#This manual page documents briefly the a2ensite and a2dissite commands.

#a2ensite  is a script that enables the specified site (which contains a
#<VirtualHost> block) within the apache2 configuration.  It does this by
#creating   symlinks   within   /etc/apache2/sites-enabled.    Likewise,
#a2dissite disables a site by removing those symlinks.   It  is  not  an
#error  to  enable  a  site  which is already enabled, or to disable one
#which is already disabled.

#The default site is handled specially: The resulting  symlink  will  be
#called 000-default in order to be loaded first.

How do I list all running processes and the amount of memory/cpu each is consuming on a linux machine?

First, start off by listing the processes that are running on your machine (i.e. their names). You can do so via the following command:

ps -e

After running the above command you'll see a list of running process and their names. Find the one you're interested in (or the one you think you're interested in) and then use its name in the following command:

ps -U www-data -u www-data u

In this case we used the name 'www-data'. You should see the instances of that process listed and the percentage of memory/cpu each is using.

Lastly, you may be wondering what the 'ps' command does (other than what you've observed here). If you run the following command, you can read all about it:

man ps

Lastly (again), the 'top' command is really awesome. It does the same stuff as the commands above but in real-time:

top

What's the best tutorial for getting set up with ruby and rails on Mac OS X?

http://createdbypete.com/articles/ruby-on-rails-development-with-mac-os-x-mountain-lion/

What's the quickest way to install homebrew on Mac OS X?

ruby <(curl -fsSkL raw.github.com/mxcl/homebrew/go)

What's the easiest way to get the latest version of ruby installed on my local *nix machine?

Using RVM (Ruby Version Manager). You can checkout the official site here: https://rvm.io/.

In short though, you can install ruby (and gems such as rails) via the following command:

curl -L https://get.rvm.io | bash -s stable --rails

How do I install a command line tool after uncompressing it?

First, you need to cd into the directory created as a result of uncompressing via tar. Something along the lines of:

cd path-to-software/

Once in the directory, run the following command:

./configure

"./configure" will configure the software to ensure your system has the necessary functionality and libraries to successfully compile the package.

If you're doing this on a Mac and you get a missing "c compiler" type error then you probably just need to install Xcode's command line tools package. To do so, simply open Xcode, go to preferences then downloads. There is an "Install" link to add the command line tools. Once this has been completed, make sure to re-open your terminal window.

Then run:

make

"make" will compile all the source files into executable binaries.

The purpose of the make utility is to determine automatically which pieces of a large program need to be recompiled, and issue the commands to recompile them.

Then run:

sudo make install

From the documentation, "make install" will copy the executable file into a directory that users typically search for commands; copy any auxiliary files that the executable uses into the directories where it will look for them (e.g. /usr/local/bin/).

Lastly, most software packages have a README or INSTALL file you should probably take a look at. You can do so by running the following command:

cat README

How do I uncompress a tarball?

To uncompress a tarball, execute the following command(s) depending on the extension:

tar zxf file.tar.gz
tar zxf file.tgz
tar jxf file.tar.bz2
tar jxf file.tbz2

The following doc snippets explain the tar options being used:

#Extract: tar -xf <archive-filename>
#-z, -j, -J, --lzma  Compress archive with gzip/bzip2/xz/lzma

Lastly, if you were to run "tar zxf file.tar.gz" you would end up with a new directory named "file" in your current directory.