Linux

One of Linux five star things is the cronjobs. They allow you to automatically run stuf (scripts, applications, etc.) at quite specific times.

The crontab is the place controlling when the stuff is run and you can list the crontab using the commaand crontab -l for the current user.

If you want to edit the crontab, just use the command crontab -e and it launches the crontab in the default editor (set EDITOR env variable to change the editor used). The format is basically like this:

My little server ran into an issue, and started reporting the error:

No space left on device

No worries, lest figure out which disk has full and clean up…

Using the df command with the -h (for human-readable output) it should be easy to find the issue:

root@server:~# df -h
Filesystem Size Used Avail Use% Mounted on
udev 483M 0 483M 0% /dev
tmpfs 100M 3.1M 97M 4% /run
/dev/vda 20G 9.3G 9.4G 50% /
tmpfs 500M 0 500M 0% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 500M 0 500M 0% /sys/fs/cgroup
cgmfs 100K 0 100K 0% /run/cgmanager/fs
tmpfs 100M 0 100M 0% /run/user/1000

Strange. Notice who the /dev/vda is 50% fillled and all other disk devices seems to be finde too. Well after a little digging, thinking and googling, it turns out device space consists of two things - space (for data) on the device and iNodes (the stuff used to mange the space - where the data go - simplified).

So I’ve installed a Raspberry Pi and it’s been running smoothly day in, day out. I’d like it to stay that way, but as the server is running it’s gathers lint in log files, databases grows and knowing how the load on CPU and memory is utilized through out time, I was looking for a tool which could help me to solve this problem.

As fun as it might be to build your own solution, I’ve learned to appreciate ready to use solutions, and it seems a nice little tool is available called RPi-Monitor. Assuming you run the Raspbian, the RPi-Monitor is available as a package ready to install through the standard package manager (once you’ve added the package repository).

As stated earlier this site is now running on a DigitalOcean droplet. A droplet is basically the same as having a “real server”, and when running a bare bones machine, it isn’t born with the ability to handle email - receiving nor sending. As a number of web apps require the ability to handle mail, I had to setup facilities on the server (or droplet) to handle mail.

The “default” way to do this would probably be to install sendmail or postfix, as they are full-featured mail server, but configuring a mail-server, keeping it secure and updated is a nightmare I’d like to avoid. Therefore it was time to look for another option.

df -lP |awk '{sum += $3} END {printf "%d GiB\\n", sum/2\*\*20}'

- via @clmagic

So, I’ve been moving the site to a VPS - a Virtual Private Server. A VPS is basically the same as a physical server to which you can’t have physical access. When you get your virtual server, most likely it will be setup with a basic disk image with an Operating System and a root account. In my case at DigitalOcean I choose to setup an Ubuntu Linux image and here are the first moves you should take after creating the VPS to get the basic security in place.

A firewall is a basic filter that can provide an efficient protection to your server by only allowing the traffic in and out as the rules of the firewall allows it. Setting up a firewall on a Ubuntu Linux server does not need to be complicated - in fact the one used in this example is called “uncomplicated firewall”.

To get the firewall up and running make sure it’s installed through the package manager. Login and switch to a root shell, then install the firewall with this command:

Sometimes there’s a need to keep a simple log in a database. A common format could be a table with a layout like this:

log

• area (char)
• lognotice (char or text)
• logtime (timestamp when the event was logged).

Fetching

Fetching all log entries from a certain area is a simple matter of fetching by the area field, but when building a dashboard with the most recent entry from each area is slightly more complicated - the Query to fetch the data could typically look like this:

This site (and my other site in Danish) have been hosted on a cheap shared hosting site a few years. As shared hosting platforms go, the service and features at GigaHost was quite reasonable, but their servers seemed continuously overloaded and the site had a few issues from time to time. I’ve been moving everything from the shared hosting platform to the smallest available VPS server at DigitalOcean.

Why the move?

• Performance on shared hosting platforms never seems to amaze.
• Limited set of features - no shell access, dummy selfcare interface, reasonable features - but limited.
• Was dirt cheap when I moved in, but not as much - the VPS is actually priced lower.

How did I move the site?

The various parts of the move will probably be described in details in further posts on the site in the foreseeable future, but basically the steps included:

VirtualBox is a free tool, which allows you to run virtual machines on a host computer. Using VirtualBox you can install Linux, Windows and other operating systems to play and experiment with.

Start the process by closing virtualbox (I usually also dettach the virtual harddisk due to be resized). Go on to a shell and find the directory where the virual machines are located.

If your initial harddisk was cloened from another virtualbox, you may get an error like this: