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Celebrating 25 Years of Linux Kernel Development

September 9, 2016 8:22 am / Leave a comment

Linux is now 25 years old, but it’s no hipster. It’s not chasing around Pokemon, and it’s not moving back in with its parents due to crippling student debt. In fact, Linux is still growing and evolving, but the core ideas of the Linux State of Mind remain the same.

You see, Linux is much more than an operating system, it’s a mindset. Even if you don’t agree with its philosophy, you can’t afford to ignore it.

That’s why we decided to pay homage to this iconic operating system and the ever-growing community of developers who keep it going.

25 years of Linux: Honoring the great penguin coup

To mark the occasion, the Linux Foundation recently published the seventh edition of its Linux Kernel Development Report, which offers a detailed recap of all the work done over the past couple of decades. The adoption of Git, 10 years ago, made tracking easier (not that we’re looking for exact numbers here). It’s estimated that more than 14,000 developers have invested time and effort in Linux kernel development since 2005. This army of talent comes from more than 1,300 companies, and the report lists a number of industry heavyweights as the main sponsors of Linux kernel development: Intel, Samsung, Red Hat, AMD, Google, ARM, Texas Instruments and more.

While it’s the epitome of open-source, Linux kernel development is not a hobby. Not anymore. So, as we wish Linux a happy birthday, let’s take a quick look at some kernel development highlights:

25 years of development
Contributions from 14,000 developers since 2005
5,000 new developers joined the effort in the past 30 months
~22 million lines of code currently constitute the Linux Kernel
More than 4,500 lines of new code added each day
Development is speeding up

Linux State of Mind

When it was first released in August 1991, few could have imagined the long-term impact of Linus Torvalds’ open-source OS on the software industry. At the time, the tech landscape was dominated by a handful of big players, the likes of Microsoft, Apple, and IBM. The nineties were an era of rapid technological progress, and new technologies – most notably the Internet – made remote, distributed development a possibility.

Developers halfway around the globe could finally collaborate on immensely complex software projects. It goes without saying that Toptal, and indeed every freelancer, owes a debt of gratitude to Linux pioneers who validated the concept of remote software development in an era of dial-up internet. They made it work, without Git, Skype, broadband, and a bunch of other technologies and tools we take for granted today. In fact, most of these tools were in part made possible by Linux-based servers and many are open-source.

But what drove the industry to adopt Linux? Well, to put it bluntly, the simple fact of not being Microsoft was a big part of it. A lot of UNIX people just had an issue with proprietary operating systems and wanted an open-source alternative. Diehards couldn’t reconcile with the fact that mainstream operating systems were a proprietary walled garden. Their vision was to create an open-source alternative, something that everyone could use free of charge, something they could modify and redistribute at will.

Idealism and business rarely cross paths, but when they do, we often end up with novel ideas backed by passionate proponents and criticized by equally passionate detractors. The idea of an open-source software ecosystem is as powerful today as it was in the early nineties, and with a quarter century of Linux development behind us, we can get a better idea of its profound impact on industry.

Open-Sourcing and Democratising The Internet

But wait, most of us are reading this on non-Linux systems: Windows and Mac rigs, smartphones and tablets running UNIX-like operating systems, so why aren’t we on Linux systems? Well, we are, at least sort of. How many LAMP servers sprung into action today, to serve you your daily dose of emails, social feed updates, useless ads and (mis)information?

Personally, I think this is the biggest contribution to mankind made by the Linux community: Linux-based servers helped our industry take off and legitimized the open-source concept.

It was no longer about UNIX enthusiasts trying to create an open-source alternative to fight The Empire; Linux took on big brands on their home turf and emerged victorious. The concept was vindicated and mainstreamed, proving once and for all that open-source isn’t just a heartwarming notion; It’s good for business.

What did we get out of it?

Linux helped lower the bar for developers and entrepreneurs entering the industry. Successful Linux distros grabbed a sizeable market share in the hosting industry, generating pressure on competing platforms. In this war of attrition, Linux servers prevailed thanks to a number of factors. In the end, they came to dominate many market segments. Today, anyone can get a reasonably powerful hosting plan for peanuts, and if they’re looking for the cheapest possible solution, they’re bound to end up with a flavor of Linux. The rest of the stack is usually as free and open as Linux itself.

That’s what our side of the industry got out of Linux: The ability to quickly deploy products on low-cost, open-source infrastructure.

How many pet projects, started on the cheap, turned into multi-billion enterprises? How many would have failed had it not been for Linux?

Where’s the Money Linuxowski?

A common misconception about Linux development is that it’s handled solely by enthusiasts and that it’s not a niche for people looking to cash in. While Linux is a labor of love, it’s also big business in its own way.

As I highlighted earlier, development is speeding up, and more Linux developers from more companies are choosing to contribute. They’re not simply choosing to set aside their precious time because they are good Linux folk; the latest report states that the number of unpaid developers working on the kernel has dropped to 7.7 percent, dipping into single-digit territory for the first time.

While some might not agree, I see this is a very positive trend. Enthusiasm doesn’t pay bills, and it’s hard to keep any project going on enthusiasm alone for more than a few years, let alone a gargantuan project like Linux that came into being a generation ago.

It doesn’t end there. According to numerous surveys, demand for Linux talent remains robust, and is actually increasing, and so is the Linux server market share. A few years ago, it would have been much easier to tally up the number of shipped servers, motherboards, and other hardware, and figure out the number of Linux boxes in the wild.

This is no longer the case.

Linux in The Cloud

A dark Cloud came along and made this process more difficult, much to the dismay of analysts. When your job is to look at numbers and market trends, any lack of data or ambiguity is bad for business, and for a while analysts expressed concerns about the future of Linux in the post-cloud era. These concerns made a lot of sense (and, to some extent, still do) because the cloud ecosystem was an oligopoly from the get-go, dominated by the Amazons and Googles of the world.

Does the Cloud spell doom for cheap Linux servers and is there a silver lining?

The Cloud did not kill off small Linux servers, but it hasn’t been kind to them either:

At one end of the spectrum, you’ll find people who believe the cloud will transform the server market, and through consolidation, will forever change the hosting industry. This economy of scale argument is tempting because it’s logical to assume cloud industry leaders will offer superior pricing by virtue of their size. You don’t get sweetheart hardware deals if you have a small, regional datacenter and need a couple of hundred fresh boxes every year; you get them if you have a massive cloud infrastructure and need dozens of new servers on a weekly basis. However, I find this argument overly simplistic.
The opposing camp espouses equally simplistic views, but it tends to be more optimistic. A lot of Linux veterans have high hopes for cloud development; they believe CloudStack and OpenStack will help turn the tide, and they think there will always be room for smaller players.

As usual, the truth is somewhere in the middle, but let’s not weigh in on this; it’s beyond the scope of this article. Suffice it to say that both options could work for Linux in the long run. Even if the hosting industry is forever transformed and consolidated, that doesn’t mean demand for Linux talent will evaporate. On the contrary, it’s likely to increase regardless of what happens, although demand will evolve to meet new requirements.

The Next 25 Years

What do the next 25 years have in store for Linux?

It’s hard to say, but I have a feeling Linux isn’t going anywhere, at least not in the foreseeable future:

The server industry is evolving, but it’s been doing so forever. Linux has a habit of seizing server market share, although the cloud could transform the industry in ways we’re just beginning to realize. Either way, Linux servers aren’t going anywhere just yet.
Linux still has a relatively low market share in consumer markets, dwarfed by Windows and OS X. This will not change anytime soon.
Linux does not have a significant share in mobile, although Android currently dominates this space. Mobile is becoming an Android/iOS duopoly. It’s oversaturated; there are too many software and hardware platforms out there, so it’s doubtful Linux will ever take off in this market.
Gaming is a potentially huge, untapped market for Linux. This market is dominated by Windows in the desktop segment, proprietary operating systems in the console space, and Android and iOS in mobile. Valve’s SteamOS is the latest attempt to get Linux on gaming rigs, and it’s a promising concept. Unfortunately, demand for Steam Machines has been soft and Linux still has a negligible market share in the gaming industry.
Emerging segments include the Internet of Things (IoT), wearables, smart home devices, and more. Due to its open-source nature and the potential for a very small OS footprint, Linux-based operating systems could find their way into a range of connected devices, from our homes and cars to our places of business.
High-performance computing has a good chance of becoming a Linux-only space. Linux has practically replaced UNIX and other operating systems in current-generation supercomputers.

It’s hard to make Linux-related predictions due to the nature of the OS and the Linux community. Evolution doesn’t necessarily have to be a straight line, and Linux developers have proven this time and again. Linux could morph into something completely different over the next couple of decades and become the OS of choice for various products and services we can’t even imagine today.

This article was written by Nermin Hajdarbegovic, a Toptal Technical Editor.

11 Essential Linux Interview Questions

September 9, 2016 8:20 am / Leave a comment

1. How would you swap the stdout and stderr of a command?

$ command 3>&2 2>&1 1>&3

To swap stdout and stderr of a command, a third file descriptor is being created (in this case 3), which is assigned to the same target that stderr is pointed to (referenced by &2). Then stderr is pointed to the same target stdout is pointed to (&1). Finally,stdout is pointed back to where the newly created file descriptor is pointed (which is the same target stderr originally pointed to.)

2. How would you count every occurrence of the term “potato” in all the files appearing under the current directory, and its subdirectories, recursively?

$ grep -orI potato . | wc -l

To list every occurrence of the term “potato” on a separate line, one must run grep -o potato <path>. Adding the r flag to the command makes the search recursively process every file under the given path, and the I flag ensures that matches in binary files are ignored. In addition, the w flag can be included to match the exact term only, and ignore superstrings such as “potatoes”, and to make the search case-insensitive, the i flag can be added as well:

$ grep -iworI potato . | wc -l

The number of lines yielded by this grep command is the number of occurrences of the desired term, which can then be counted by piping it into the wc -l command.

3. How would you write a shell script that prints all the additional arguments passed to it in reverse order?

for (( i = ${#}; i > 0; i-- )); do
        echo ${!i}
done

The arguments are available as $<n>, where n is the position of the argument. For example, $0 would give the name of the script, $1 would give the first additional argument, $2 the second, and so on. The total number of additional arguments is found in $#.

A loop that starts at $# and ends at 1 can be used to print each additional argument in reverse order.

4. How would you write a shell script and ensure that only one instance of the script may run for every user? Strong atomicity is not required.

In Bash:

LOCKFILE=/tmp/lock-`whoami`
if [ -e ${LOCKFILE} ] && kill -0 `cat ${LOCKFILE}`; then
    echo "Already running!"
    exit 1
fi
trap "rm -f ${LOCKFILE}; exit" INT TERM EXIT
echo $$ > ${LOCKFILE}

Start by determining a name for the lock file. In this case, the lock file is generated by suffixing a common name with the username of the current user.

Then, check if the lock file exists and if the PID contained within the lock file is running. If it is, exit with a message.

Create a trap to remove the lock file on a clean exit, or unclean exits (any exit with the signal INT or TERM).

Finally, if the script has not exited yet, create the lock file, and store the PID of the current process ($$) in it.

5. What are shared, slave, private, and unbindable mountpoints?

A mount point that is shared may be replicated as many times as needed, and each copy will continue to be the exact same. Other mount points that appear under a shared mount point in some subdirectory will appear in all the other replicated mount points as it is.

A slave mount point is similar to a shared mount point with the small exception that the “sharing” of mount point information happens in one direction. A mount point that is slave will only receive mount and unmount events. Anything that is mounted under this replicated mount point will not move towards the original mount point.

A private mount point is exactly what the name implies: private. Mount points that appear under a private mount point will not be shown elsewhere in the other replicated mount points unless they are explicitly mounted there as well.

An unbindable mount point, which by definition is also private, cannot be replicated elsewhere through the use of the bind flag of the mount system call or command.

6. What are some basic measures that you would take to harden a server’s SSH service?

There are a some very simple steps that can be taken to initially harden the SSH service, such as:

Forcing the service to use only version 2 of the protocol will introduce both security and feature enhancement.
Disabling root login, and even password-based logins, will further reinforce the security of the server.
The whitelist approach can be taken, where only the users that belong to a certain list can login via SSH to the server.
Disabling password-based login will require you to then allow key based logins, which is secure, but can be taken further by restricting their use from only certain IP addresses.
Changing the port to something other than 22 significantly decreases random brute force attempts from the internet.

Sometimes the use of having an SSH service on a server may just be transferring files to and from the server (typically using tools like scp). In such a case, it is possible to change the shell of the user to something restrictive, such as rssh.

Finally it is often desirable to know exactly what is going on while you are not logged into the server. The logging verbosity may be increased if needed. Often, it is the logs that allow one to figure out if a key has indeed been stolen and is being abused.

7. What is a Unix shell? Is Bash the only Unix shell?

A Unix shell is a software that provides a user interface for the underlying operating system. Unix shells typically provide a textual user interface – a command line interpreter – that may be used for entering and running commands, or create scripts that run a series of commands and can be used to express more advanced behavior.

Bash is not the only Unix shell, but just one of many. Short for Bourne-Again Shell, it is also one of the many Bourne-compatible shells. However, Bash is arguably one of the most popular shells around. There are other, modern shells available that often retain backwards compatibility with Bash but provide more functionality and features, such as the Z Shell (zsh).

8. Where is the target path of a symlink stored? How are permission settings for symlinks handled?

The target path of a symlink is stored in an inode – the data structure used to store file information on disk.

Typically, the permission settings of the symlink itself only control the renaming and removal operations performed on the symlink itself. Any operation that deals with the contents of the file linked to are controlled by the permission settings of the target file.

9. What are terminal multiplexers? What are some of their key features? What are some of the more popular ones currently available?

Terminal multiplexers enable several terminals to be created and controlled from a single screen or from a single remote session. The terminals and sessions can be detached and left running, even with the user logging off.

Two of the more common ones available today are GNU Screen and tmux.

Screen enables you to connect to multiple remote servers without needing to open multiple terminal shells. Work can be preserved and a session detached, for example, to wait for the output of a long-running command. On subsequent reconnection, users can reattach to existing sessions or run new sessions. Sessions can also be shared among different users, which may be useful in audit or training scenarios.

Both Screen and tmux support split-screen functionality (to be more precise, tmux supports this and Screen supports it via a plugin). This allows, for example, runningtail on a service’s log file in one part of the screen, and editing the configuration of that service, and restarting it if necessary, in another.

10. What would be a simple way to continuously monitor the log file for a service that is running?

Probably the simplest and most common way to do this would be by using the command:

tail -F $LOGFILE

where $LOGFILE is an environment variable corresponding to the path to the log file to be monitored.

By default, the Linux tail command prints the last 10 lines of a given file to standard output. The -F option causes additional file content to be displayed in realtime as the file continues to grow. This yields a simple mechanism for monitoring services via their log files in close to realtime.

Two other specific command line options of interest in this context are:

The -s option causes tail to sleep for a specified number of seconds between updates (e.g., tail -F -s 10 will update the displayed file contents roughly every 10 seconds rather than in close to realtime as the file is updated).
The -n option can be used to specify a number of lines other than 10 to initially display (e.g., tail -n 20 -F will first display the last 20 lines of the file and will then continue updating the output in realtime).

11. What is a Linux null (or Blackhole) route? How can it be used to mitigate unwanted incoming connections?

A Linux null (or Blackhole) route is a type of routing table entry which, upon matching a packet, discards it without forwarding the packet any further or sending any ICMP.

Using this technique, it is possible to block an IP (or range of IP addresses) by running a simple command. For example, blocking 192.168.0.1 can simply be done with the following command:

# ip route add blackhole 192.168.0.1/32

This article is from Toptal.

video installation SAP NetWeaver 7.4 using Oracle 12c on SuSE Linux Enterprise Server 11 SP 4

November 30, 2015 2:14 pm / Leave a comment

This video show you on step by step installation of SAP NetWeaver 7.4 using Oracle 12c as database server on SuSE Linux Enterprise Server 11 SP 4.

Preparation :

Installation part 1 :

Installation part 2 :

Installation part 3 :

Installation part 4 :

Enjoy !!

Video Step by step upgrade SLES 11 SP 4 (with SAP ERP 6 EHp 5) to SLES 12

October 26, 2015 12:11 am / Leave a comment

This video show you on how to step by step upgrade SuSE Linux Enterprise Server 11 SP 4 (with SAP ERP 6 EHp 5 on it) to SuSE Linux Enterprise Server 12.

There are few problems especially on uuidd (UUID daemon) and libuuid1 but it all solved. You can check it out.

Happy watching !!

Video Upgrade SLES 11 SP 2 with SAP ERP 6 EHp 5 to SLES 11 SP4

October 24, 2015 9:42 am / Leave a comment

I have installed SAP ERP 6 EHp 5 on SuSE Linux Enterprise Server SP 2. Then I need to upgrade my OS from SLES 11 SP 2 to the latest version of SLES 11, which is SLES 11 SP 4.

Here are the video.