How Many Linux Systems Do You Use? Don’t Answer Too Quickly

linux-154544_640

“Linux? Where you have to type everything and it’s all a bunch of cryptic nonsense like this?
ls -laRF | less
I don’t use it, I never would!”

Don’t answer so fast.

While Linux runs 97% of the top 500 supercomputers in the world, it runs on many devices you encounter in everyday life. And it’s not just Android phones.

Raspberry Pi single-board low-cost Linux computer
Raspberry Pi single-board Linux computer

Linux is a big part of the “Internet of Things.” In most of those applications it’s buried so far inside that you will never notice it unless you very carefully read the paperwork that comes with a new purchase (yeah, right) or you become curious enough to carry out your own investigation.

The Raspberry Pi Linux system that goes for $25-35 is the best known single-board computer, but there are also a lot of BeagleBones out there. They’re the visible side of a booming industry of very low-cost computers about 2×3 inches in size.

Do You Travel By Air?

Airline seatback entertainment systems tend to run Linux. You can’t tell while it’s running, as the interface is a simple panel of buttons to poke, but sometimes you will see them reset the systems if you have boarded early. Tux the penguin mascot appears on all seatbacks, followed by the console boot narrative sequence.

Do You Watch Movies At Home?

I had been very happy with a Philips DVD player, and when it finally gave out I bought a Philips Blu-ray player to replace it. Hmmm, there’s an Ethernet port on the back, and its hardware address is printed on the rear panel. I’ll plug it into my Ethernet switch, and I’ll start Wireshark and capture its traffic. It connects to the manufacturer every time it starts, to see if any software update is available.

I had noticed that the paperwork included what first appeared to be a small booklet but turned out to be a large sheet of very thin paper. Fully unfolded to 2×3 feet, it was a large collection of open-source licences for a wide variety of software, including the Linux kernel. It also included a few non-open-source licenses for some codecs, including MP3, MPEG, and Microsoft’s WMA and WMV audio and video formats. An nmap scan revealed that the player runs Linux.

I started mentioning that Philips Blu-ray players ran Linux when I taught Learning Tree’s Linux server administration course. Then one week an engineer from Sony was in the room, he laughed and said that they all run Linux.

“All Sony players also run Linux?”

“No, all DVD players other than the really low-end ones. If there is an Ethernet jack in the back, or 802.11 wireless network connectivity, it runs Linux.”

I also get to learn in these courses!

Do You Use Electricity and Water?

A student in a recent run of the Linux server administration course worked at a company that manufactures utility meters for electricity, water, and gas companies. All their products are based on embedded Linux single-board computers, the same as most if not all of their competitors.

Is Your Home Connected To The Internet?

I only recently noticed that my Motorola Arris SURFboard cable modem runs Linux. I had to replace the old cable modem, and was curious about the new one. Nmap revealed that it runs Linux.

# nmap cablemodem
Starting Nmap 6.47 ( http://nmap.org ) at 2015-11-24 10:29 EST
Nmap scan report for cablemodem (192.168.100.1)
Host is up (0.00035s latency).
Not shown: 997 closed ports
PORT    STATE    SERVICE      VERSION
80/tcp  open     http         NET-DK 1.0
139/tcp filtered netbios-ssn
445/tcp filtered microsoft-ds
Device type: general purpose
Running: Linux 2.6.X
OS CPE: cpe:/o:linux:linux_kernel:2.6
OS details: Linux 2.6.9 - 2.6.33

Checking further, a Netgear DSL router shows this:

# nmap 192.168.254.254
Starting Nmap 6.47 ( http://nmap.org ) at 2015-11-27 12:41 EST
Nmap scan report for dslrouter.netgear.com (192.168.254.254)
Host is up (0.0024s latency).
Not shown: 996 closed ports
PORT     STATE SERVICE    VERSION
53/tcp   open  domain     dnsmasq 2.40
80/tcp   open  http       GoAhead-Webs embedded httpd
443/tcp  open  ssl/http   GoAhead-Webs embedded httpd
4567/tcp open  tcpwrapped
Device type: general purpose
Running: Linux 2.6.X
OS CPE: cpe:/o:linux:linux_kernel:2.6
OS details: Linux 2.6.15 - 2.6.26 (likely embedded)

Just last week, someone shared an interesting paper about NTP (or the Network Time Protocol). It’s “Attacking the Network Time Protocol“, by several researchers at Boston University. In the course of their research they did a zmap scan of what they casually refer to as “the IPv4 address space,” meaning all the IPv4 addresses out there. They wanted to take a census of the IPv4 NTP devices out there: what versions of NTP were running on publicly reachable hosts, and what percentage of them had a vulnerability?

I found it puzzling that out of the 10,110,131 responding NTP hosts, the vast majority of those running some form of Linux were running 2.* kernels. Since the 3.0 kernel released in July, 2011, that seemed strange.

Rank Version Number
1 2.6.18 123,780
2 2.4.23 108,828
3 2.6.32 97,168
4 2.4.20 90,025
5 2.6.19 71,581
6 2.4.18 68,583
7 2.6.27 61,301
8 2.6.36 45,055

A large percentage of these 2.* Linux devices must be home cable/DSL modems. The zmap scan could reach them, and they responded to NTP, but they weren’t what we would normally think of as Linux systems.

Food for thought: My Blu-ray player checks for updates every time I start it, and it is protected behind my address-translating firewall. As far as I can tell, my cable modem never checks for an update and it’s exposed to the Internet.

image sources

  • raspberry-pi-4717: Bob Cromwell

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