Adding cronjobs using crontab in Ubuntu 12.04/Mint 13

Cronjobs are a good way to run a script every so often (hour, day, week, at reboot, etc.) Some things I use it for are:
To keep my public ip address updated and saved in my Dropbox folder,
To mount my external hard drive on my ubuntu server every time it reboots,
And to update my psmouse-alps driver which needs to be updated at reboot as well.

I'm sure someone else can find many other possible more useful applications for this.

First think you need to do is find out what privileges you need to do what you want to do. Since all i need to update my public ip is access to the internet and also my dropbox folder, I only needed my regular user privileges.

Crontab has some pretty good explanations and even gives you an example in the comment in the file. The first 5 fields (separated by spaces) are to tell it when/how often you want to run a certain command/script. Right after the first five fields you just put the command/script you want to run.
The example used in the file:

0 5 * * 1 tar -zcf /var/backups/home.tgz /home/

I found some pretty good examples to help you to understand the schedule notation that crontab uses. Wikipedia has a useful article here. Also this site was very useful. What I found was also very useful was some of the shortcuts, listed here.
They are:

@reboot
@yearly
@annually
@monthly
@weekly
@daily
@midnight
@hourly 

So on my ubuntu server, since I need root privileges to mount my external drive, I edit the crontab by executing:

sudo crontab -e

Then I choose to edit it with vim since it is my preferred text editor, and add this line to have my external hard drive mount at boot:

@reboot mount -t ntfs-3g /dev/sdb1 /media/external

And to have my ip update every day I run:

crontab -e

(as a regular user, I don't need root for this)

and have it run my script to update the ip daily:

@daily /home/user/bin/ip_script

For any interested my script is very simple(3 lines), and only needs the curl utility installed.

sudo apt-get install curl

also dropbox if you don't already have it.

then open a text editor and write

#! /bin/bash

curl ifconfig.me >> public_ip

mv public_ip ~/Dropbox/

Then name and save the file, make it executable and add it to crontab.

Setting up opendns.com with Ubuntu 12.04/Mint 13

opendns.com is a great service for blocking and/or tracking web access. Although most people probably have a dynamic ip address, and it can be difficult to find a good way to keep your ip up to date with their site and servers. This is the way I found the easiest for me.

Go to www.opendns.com click on 'Sign In' in the top right corner. Then click on the Get Started! link and set up an account. I would suggest either of the free accounts. The only difference is that the FamilyShield account is preconfigured. I ended up configuring it myself anyway.

Then log in. Go to the Settings tab. Your own ip should be at the very top of the page(above the nav bar). You can use that to add your network. Once you have added your network you can click on your network/ip and set up your filtering preferences.
allowed on this network.
Now the way I chose to set my network up to go through the opendns servers was by configuring the ip addresses of the opendns servers on my router. This can be different depending on your router, mine was very simple. There was a place to specify static dns servers. I just entered the ip's (they can be found on the opendns website at the bottom of the page.) saved the configuration and all my web traffic was now going through the opendns servers.

Once you get to this point, if you try to visit a blocked site it should come up with an opendns site telling you the domain is blocked. If you have a static ip, then at this point you are done. Most of us I would imagine have a dynamic ip and need to set something up so that this will stay updated. I used DNS-O-Matic provided by same people who made opendns

Go to DNS-O-Matic website: http://www.dnsomatic.com/
Since it is an opendns service you don't need to create an account, you can use the one you just created with opendns.
Click on Sign In, use your opendsn username & password.
Click on the 'Add a service' button and select OpenDNS from the drop down list.
It will add the opendns service and then the status will be waiting for confirmation or something similar.

Now is the fun part. I found my preferred method to keep this up to date was by using ddclient. In a terminal type:
sudo apt-get install ddclient
It will then ask you a bunch of questions. I tried to match this as close as possible although, the questions and names for things are slightly different so it doesn't matter too much what you put in there since we will go to the config file and change it anyways.
After it is installed open up with sudo/root priviledges /etc/ddclient.conf in your favorite text editor. For me:
sudo vim /etc/ddclient.conf

and make it look like this.
The only unique change you need are your username and password, everything else you want to match the file in the previous link. Save the file and run: sudo ddclient

Now you can run ddclient every time your ip changes and it will keep everything updated or you can add it as a cron job, I would say once a day would be enough for most any isp. See how here.

Regular things I do after a fresh install. (Ubuntu 12.04/Mint 13)

Here's some things I like to do after a fresh install of ubuntu/mint.

Install apt-fast:

sudo add-apt-repository ppa:apt-fast/stable
sudo apt-get update; sudo apt-get install apt-fast

Then update(I always use apt-fast since I know there will be a lot to download):
sudo apt-fast update; sudo apt-fast upgrade

Install vim from apt(if not already installed)

Edit my /etc/hosts file to include all of the computers on my home network. Copy over files that I backed up on those computers.

Disable apport(if ubuntu. if mint then disable after installing software-center):
sudo vim /etc/default/apport   --- change '1' to '0' and save.
sudo service apport stop

Install chromium-browser use apt
Install chrome from .deb file
Install google-earth from .deb
Install google music manager from .deb
Install google talk plugin from .deb
Install teamviewer from .deb
Install VMware Player from .bundle (rename from .txt when saving(yes you can just still execute it regardless... just change it... because.))
Install synapse from apt
Install fogger:

sudo add-apt-repository ppa:loneowais/fogger
(update; and install fogger)

Install gimp if not at least 2.8(because I like the single window mode)

sudo add-apt-repository ppa:otto-kesselgulash/gimp
(update; and install gimp)

Install dropbox from apt
run/setup dropbox

Tmux basics

Using tmux. What is tmux? How does it work and what's it useful for? Someone once recommended tmux as something useful to use. So I started looking into it without really knowing what it was. Here I'll tell you how it's actually useful to me. So, what is it? Here's what they have to say about it on sourceforge. "tmux is a terminal multiplexer. What is a terminal multiplexer? It lets you switch easily between several programs in one terminal, detach them (they keep running in the background) and reattach them to a different terminal. And do a lot more. See the manual."

Well that didn't make much sense to me and it took a bit of searching around and reading manuals and the like to find out how tmux would actually be useful to me. 
For me tmux is pretty much just a way to run multiple terminals inside of one. Here's mine with 3 terminals open:

It just looks like one of course(you can only type into one at a time). If you look at the green bar at the bottom you can see the names of each: 0:bash, 1:bash~, 2:bash*

So far this hasn't impressed me. I mean, that's just like having different tabs right? I can even do that with the terminal so that's not useful unless maybe I was on a server install. -- True. Where tmux really becomes useful is with it's ability to detach and attach sessions. I have 3-4 different computers(one isn't on too much) and I'm too lazy to get up and go to each computer when I find something cool that I want to install on all my computers, or when they all need to be updated. A lot of the time when I am at home it's not a problem to simply leave a terminal open connected to one of the computers via ssh while it installs something/updates/while running a script. Although if I decide I do want to get off my lazy but and go to one of the other computers(for instance from my laptop to my desktop) then I have to make sure the laptop stays up and running, or I have to kill the command and rerun it on the computer when I get there. If I am using tmux however I can simply detach the session, and reattach it when I get to the other computer. 

Where I find I get the most use out of tmux is when I am connecting to a school server, or when I am connecting on my laptop from somewhere other than home. When connecting from somewhere other than home(and especially if I am installing something/running a script that will take a while I can't be sure that my in-laws internet will stay connected the whole time(if you look a the box(modem) wrong it disconnects). With tmux I can start apt-get then detach and it will be running in the background the whole time... and I don't need to be connected to that computer via ssh.

So now that I've bored you all with the usefulness of tmux for me, here's a few simple commands that I use that can hopefully get you started. If you start to find it useful and want to use it more I recommend going to one of the other sites out there to see more things you can do with it.

To start tmux simply type the command:

    tmux

To open a new terminal instance:

    Ctrl+b c

To close a terminal:

    Ctrl+b x

To go to the next terminal:

    Ctrl+b n

To detach the session:

    Ctrl+b d

To reattach after detaching use command:

    tmux attach

UPDATE: Wow I just realized this post is pretty long. For a crash course just install tmux and play with the above commands in the last paragraph. After learning and using tmux a bit more I'd say its time to add some more commands.

I simply looked at the man pages and created a cheat sheet of just the commands here.

Some of the main ones I'm using aside from the above are:

To split terminal  vertically:

   Ctrl+b %

To split horizontally:

   Ctrl+b "

To navigate through existing panes:

   Ctrl+b LEFT,RIGHT,UP,DOWN

Holding Ctrl+b down while using the navigation buttons will resize your current pane.