Twitter
Home Blog Page 315

GCC: Optimizing Linux, the Internet, and Everything

By
Margaret Lewis
-

Software is useless if computers can’t run it. Even the most talented developer is at the mercy of the compiler when it comes to run-time performance – if you don’t have a reliable compiler toolchain you can’t build anything serious. The GNU Compiler Collection (GCC) provides a robust, mature and high performance partner to help you get the most out of your software. With decades of development by thousands of people GCC is one of the most respected compilers in the world. If you are building applications and not using GCC, you are missing out on the best possible solution.

GCC is the “de facto-standard open source compiler today” [1] according to LLVM.org and the foundation used to build complete systems – from the kernel upwards. GCC supports over 60 hardware platforms, including ARM, Intel, AMD, IBM POWER, SPARC, HP PA-RISC, and IBM Z, as well as a variety of operating environments, including GNU, Linux, Windows, macOS, FreeBSD, NetBSD, OpenBSD, DragonFly BSD, Solaris, AIX, HP-UX, and RTEMS. It offers highly compliant C/C++ compilers and support for popular C libraries, such as GNU C Library (glibc), Newlib, musl, and the C libraries included with various BSD operating systems, as well as front-ends for Fortran, Ada, and GO languages. GCC also functions as a cross compiler, creating executable code for a platform other than the one on which the compiler is running. GCC is the core component of the tightly integrated GNU toolchain, produced by the GNU Project, that includes glibc, Binutils, and the GNU Debugger (GDB).

“My all-time favorite GNU tool is GCC, the GNU Compiler Collection. At a time when developer tools were expensive, GCC was the second GNU tool and the one that enabled a community to write and build all the others. This tool single-handedly changed the industry and led to the creation of the free software movement, since a good, free compiler is a prerequisite to a community creating software.” —Dave Neary, Open Source and Standards team at Red Hat. [2]

Optimizing Linux

As the default compiler for the Linux kernel source, GCC delivers trusted, stable performance along with the additional extensions needed to correctly build the kernel. GCC is a standard component of popular Linux distributions, such as Arch Linux, CentOS, Debian, Fedora, openSUSE, and  Ubuntu, where it routinely compiles supporting system components. This includes the default libraries used by Linux (such as libc, libm, libintl, libssh, libssl, libcrypto, libexpat, libpthread, and ncurses) which depend on GCC to provide correctness and performance and are used by applications and system utilities to access Linux kernel features. Many of the application packages included with a distribution are also built with GCC, such as Python, Perl, Ruby, nginx, Apache HTTP Server, OpenStack, Docker, and OpenShift. This combination of kernel, libraries, and application software translates into a large volume of code built with GCC for each Linux distribution. For the openSUSE distribution nearly 100% of native code is built by GCC, including 6,135 source packages producing 5,705 shared libraries and 38,927 executables. This amounts to about 24,540 source packages compiled weekly. [3] 

The base version of GCC included in Linux distributions is used to create the kernel and libraries that define the system Application Binary Interface (ABI). User space developers have the option of downloading  the latest stable version of GCC to gain access to advanced features, performance optimizations, and improvements in usability. Linux distributions offer installation instructions or prebuilt toolchains for deploying the latest version of GCC along with other GNU tools that help to enhance developer productivity and improve deployment time.

Optimizing the Internet

GCC is one of the most widely adopted  core compilers for embedded systems, enabling the development of software for the growing world of IoT devices. GCC offers a number of extensions that make it well suited for embedded systems software development, including fine-grained control using compiler built-ins, #pragmas, inline assembly, and application-focussed command-line options. GCC supports a broad base of embedded architectures, including ARM, AMCC, AVR, Blackfin, MIPS, RISC-V,  Renesas Electronics V850, and NXP and Freescale Power-based processors, producing efficient, high quality code. The cross-compilation capability offered by GCC is critical to this community, and prebuilt cross-compilation toolchains [4] are a major requirement. For example, the GNU ARM Embedded toolchains are integrated and validated packages featuring the Arm Embedded GCC compiler, libraries, and other tools necessary for bare-metal software development. These toolchains are available for cross-compilation on Windows, Linux and macOS host operating systems and target the popular ARM Cortex-R and Cortex-M processors, which have shipped in tens of billions of internet capable devices. [5]

GCC empowers Cloud Computing, providing a reliable development platform for software that needs to directly manages computing resources, like database and web serving engines and backup and security software. GCC is fully compliant with C++11 and C++14 and offers experimental support for C++17 and C++2a [6], creating performant object code with a solid debugging information.  Some examples of applications that utilize GCC include: MySQL Database Management System, which requires GCC for Linux [7]; the Apache HTTP Server, which recommends using GCC [8]; and Bacula, an enterprise ready network backup tool which require GCC. [9]  

Optimizing Everything

For the research and development of the scientific codes used in High Performance Computing (HPC), GCC offers mature C, C++, and Fortran front ends as well as support for OpenMP and OpenACC APIs for directive-based parallel programming. Because GCC offers portability across computing environments, it enables code to be more easily targeted and tested across a variety of new and legacy client and server platforms.  GCC offers full support for OpenMP 4.0 for C, C++ and Fortran compilers and full support for OpenMP 4.5 for C and C++ compilers. For OpenACC, GCC supports most of the  2.5 specification and performance optimizations and is the only non-commercial, nonacademic compiler to provide OpenACC support.

Code performance is an important parameter to this community and GCC offers a solid performance base.  A Nov. 2017 paper published by Colfax Research evaluates C++ compilers for the speed of compiled code parallelized with OpenMP 4.x directives and for the speed of compilation time. Figure 1 plots the relative performance of the computational kernels when compiled by the different compilers and run with a single thread. The performance values are normalized so that the performance of G++ is equal to 1.0.

Figure 1. Relative performance of each kernel as compiled by the different compilers. (single-threaded, higher is better).

The paper summarizes “the GNU compiler also does very well in our tests. G++ produces the second fastest code in three out of six cases and is amongst the fastest compiler in terms of compile time.” [10]

Who Is Using GCC?

In The State of Developer Ecosystem Survey in 2018 by JetBrains, out of 6,000 developers who took the survey GCC  is regularly used by 66% of C++ programmers and 73% of C programmers. [11] Here is a quick summary of the benefits of GCC that make it so popular with the developer community.

  • For developers required to write code for a variety of new and legacy computing platforms and operating environments, GCC delivers support for the broadest range of hardware and operating environments. Compilers offered by hardware vendors focus mainly on support for their products and other open source compilers are much more  limited in the hardware and operating systems supported. [12]

  • There is a wide variety of GCC-based prebuilt toolchains, which has particular appeal to embedded systems developers. This  includes the GNU ARM Embedded toolchains and 138 pre-compiled cross compiler toolchains available on the Bootlin web site. [13] While other open source compilers, such as Clang/LLVM, can replace GCC in existing cross compiling toolchains,  these would need to be completely rebuilt by the developer. [14]

  • GCC delivers to application developers trusted, stable performance from a mature compiler platform. The GCC 8/9 vs. LLVM Clang 6/7 Compiler Benchmarks On AMD EPYC article provides results of 49 benchmarks ran across the four tested compilers at three optimization levels. Coming in first 34% of the time was GCC 8.2 RC1 using “-O3 -march=native” level, while at the same optimization level LLVM Clang 6.0 came in second with wins 20% of the time. [15]

  • GCC delivers improved diagnostics for compile time debugging [16] and accurate and useful information for runtime debugging. GCC is tightly integrated with GDB, a mature and feature complete tool which offers ‘non-stop’ debugging that can stop a single thread at a breakpoint.

  • GCC is a well supported platform with an active, committed community that supports the current and two previous releases. With releases schedule yearly this provides two years of support for a version.

GCC: Continuing to Optimize Linux, the Internet, and Everything

GCC continues to move forward as a world-class compiler. The most current version of GCC is 8.2, which was released in July 2018 and added hardware support for upcoming Intel CPUs, more ARM CPUs and improved performance for AMD’s ZEN CPU. Initial C17 support has been added along with initial work towards C++2A. Diagnostics have continued to be enhanced including better emitted diagnostics, with improved locations, location ranges, and fix-it hints, particularly in the C++ front end. A blog written by David Malcolm of Red Hat in March 2018 provides an overview of usability improvements in GCC 8. [17]

New hardware platforms continue to rely on the GCC toolchain for software development, such as RISC-V, a free and open ISA that is of interest to machine learning, Artificial Intelligence (AI), and IoT market segments. GCC continues to be a critical component in the continuing development of Linux systems. The Clear Linux Project for Intel Architecture, an emerging distribution built for cloud, client, and IoT use cases, provides a good example of how GCC compiler technology is being used and improved to boost the performance and security of a Linux-based system. GCC is also being used for application development for Microsoft’s Azure Sphere, a Linux-based operating system for IoT applications that initially supports the ARM based MediaTek MT3620 processor. In terms of developing the next generation of programmers, GCC is also a core component of the Windows toolchain for Raspberry PI, the low-cost embedded board running Debian-based GNU/Linux that is used to promote the teaching of basic computer science in schools and developing countries.

GCC was first released on March 22, 1987 by Richard Stallman, the founder of the GNU Project and was considered a significant breakthrough since it was the first portable ANSI C optimizing compiler released as  free software. GCC is maintained by a community of programmers from all over the world under the direction of a steering committee that ensures broad, representative oversight of the project. GCC’s community approach is one of its strengths, resulting in a large and diverse community of developers and users that contribute to and provide support for the project. According to Open Hub, GCC “is one of the largest open-source teams in the world, and is in the top 2% of all project teams on Open Hub.” [18]

There has been a lot of discussion about the licensing of GCC, most of which confuses rather than enlightens. GCC is distributed under the GNU General Public License version 3 or later with the Runtime Library Exception. This is a copyleft license, which means that derivative work can only be distributed under the same license terms. GPLv3 is intended to protect GCC from being made proprietary and requires that changes to GCC code are made available freely and openly. To the ‘end user’ the compiler is just the same as any other; using GCC makes no difference to any licensing choices you might make for your own code. [19]

Notes

 3. Information provided by SUSE based on recent build statistics. There are other source packages in openSUSE that do not generate an executable image and these are not included in the counts.
 

Margaret Lewis is a technology consultant who previously served as Director of Software Planning at AMD and an Associate Director at the Maui High Performance Computing Center.  

Thanks to the GCC Steering Committee and GNU Cauldron participants for their support and feedback on early drafts of this paper.

How Linux Is Changing The Face Of End-User Computing

By
Forbes
-

End-user computing (EUC) is changing quickly, and dramatically. In my work, I hear just how vital it is that organizations deliver better security, manageability and user experience every day. This is creating increasing pressure on the status quo of operating systems for end-user devices: Windows. And Windows simply can’t keep up with the requirements.

What you may not know is that this pressure is also giving rapid rise to the broad use of Linux on endpoint devices. In fact, according to a new IDC InfoBrief, Linux is the only endpoint operating system (OS) growing at a global level. (Full disclosure: IGEL sponsored the report.) While Windows market share remains flat, at 39% in 2015 and 2017, Linux has grown from 30% in 2015 to 35% in 2017, worldwide. And the trend is accelerating.

So, what is it about Linux that makes it so attractive for endpoint devices? Consider these factors:

Read more at Forbes

Add It Up: FaaS ≠ Serverless

By
The New Stack
-

Serverless architecture is not needed to use Function as a Service (FaaS). In fact, 54 percent of FaaS users without production deployments say their organization does not utilize a serverless architecture, according to a survey conducted in August 2018. In comparison, 96 percent of organizations with FaaS broadly deployed say they use a serverless architecture. Our upcoming Guide to Serverless Technologies covers serverless architecture, technology and computing, and will include the complete study results.

The survey defined FaaS as typically providing event-driven computing where developers run and manage application code with functions that are triggered by events or HTTP requests. Serverless architecture broadly describes an application design that incorporates third-party Backend as a Service (BaaS) services, and/or that includes custom code run in managed environments on a FaaS platform. In many ways, serverless architecture looks similar to other application designs focused on events and microservices.

Read more at The New Stack

 

Get Essential Security Information from Linux Security Summit Videos

By
Amber Ankerholz
-

In case you missed it, videos for Linux Security Summit NA are now available. On Linux.com, we covered a couple of these in depth, including:

Redefining Security Technology in Zephyr and Fuchsia By Eric Brown

If you’re the type of person who uses the word “vuln” as a shorthand for code vulnerabilities, you should check out the presentation from the recent Linux Security Summit called “Security in Zephyr and Fuchsia.” In the talk, two researchers from the National Security Agency discuss their contributions to the nascent security stacks of two open source OS projects: Zephyr and Fuchsia.

Building Security into Linux-Based Azure Sphere By Eric Brown

Microsoft’s Ryan Fairfax explained how to fit an entire Linux stack into 4 MiB of RAM in this presentation. Yet, the hard part, according to Fairfax, was not so much the kernel modification, as it was the development of the rest of the stack. This includes the custom Linux Security Module, which coordinates with the Cortex-M4’s proprietary Pluton security code using a mailbox-based protocol.

Greg Kroah-Hartman Explains How the Kernel Community Is Securing Linux By Swapnil Bhartiya

In this article, Swapnil Bhartiya interviewed Linux kernel maintainer Greg Kroah-Hartman about how the kernel community is hardening Linux against vulnerabilities. You can see excerpts from their talk in the accompanying video.

The entire list of 27 videos from the event also includes:

The next Linux Security Summit Europe, coming up October 25 – 26 in Edinburgh, offers more essential security information, with refereed presentations, discussion sessions, subsystem updates, and more. There’s still time to register and attend! Check out the full schedule and stay tuned for more coverage.

You can also sign up to receive event updates:

Auto Industry’s Thirst for Software is Quenched by Open Source

By
Automotive World
-

“It is very surprising to people just how much open source software is used in modern software development,” observed Jeff Luszcz, Vice President of Product, Management at US software specialist Flexera, during a recent Automotive World webinar. According to Flexera research, more than 50% of all code written today is open source. “If we look at any software product ten to 20 years ago, OSS was just filling in the gaps, but my experience is that 100% of IT organisations are using OSS today.”

Digital trends

Software content has become a differentiator for automakers, who had once relied on factors such as drivability or exterior design to sell their cars. Today, software-based features are often the focal point for advertising campaigns.

This software is derived from a multitude of different sources, and rarely originates from a single developer. Many vehicles today leverage Linux, an open source operating system. “Every device in a modern vehicle contains anywhere between 80 to 100 million lines of code. Some vendors have ten or more Linux computers running at the same time, and while these computers may have very similar software stacks, they will likely have been put together by different development teams, and have different reasons for existing,” added Luszcz.

Read more at Automotive World

The Future of Networking: Open Source Networking Is the ‘New Norm’

By
Network World
-

Open source networking has become the ‘new norm,’ and many at the recent Open Networking Summit Europe said they’re seeing it play out in the industry.

If you weren’t in Amsterdam for Open Networking Summit Europe 2018, you missed an extremely exciting conference This Linux Foundation event drew more than 700 networking, development and operations leaders and enterprise users from open source service providers, cloud companies, and more.

Chief among the conference themes was the idea that open source networking is the “new norm,” with lots of vendors attesting to how this theme is playing out in the IT industry. Dan Kohn who leads the Linux Foundation’s Cloud Native Computing Foundation cites cost savings, improved resilience and higher development velocity for both bug fixes and the rolling out of new features for this change. Arpit Joshipura, General Manager of Networking at The Linux Foundation used the term “open-sourcification” in his keynote.

Read more at Network World

Open Source Logging Tools for Linux

By
Jack Wallen
-

If you’re a Linux systems administrator, one of the first tools you will turn to for troubleshooting are log files. These files hold crucial information that can go a long way to help you solve problems affecting your desktops and servers. For many sysadmins (especially those of an old-school sort), nothing beats the command line for checking log files. But for those who’d rather have a more efficient (and possibly modern) approach to troubleshooting, there are plenty of options.

In this article, I’ll highlight a few such tools available for the Linux platform. I won’t be getting into logging tools that might be specific to a certain service (such as Kubernetes or Apache), and instead will focus on tools that work to mine the depths of all that magical information written into /var/log.

Speaking of which…

What is /var/log?

If you’re new to Linux, you might not know what the /var/log directory contains. However, the name is very telling. Within this directory is housed all of the log files from the system and any major service (such as Apache, MySQL, MariaDB, etc.) installed on the operating system. Open a terminal window and issue the command cd /var/log. Follow that with the command ls and you’ll see all of the various systems that have log files you can view (Figure 1).

Figure 1: Our ls command reveals the logs available in /var/log/.

Say, for instance, you want to view the syslog log file. Issue the command less syslog and you can scroll through all of the gory details of that particular log. But what if the standard terminal isn’t for you? What options do you have? Plenty. Let’s take a look at few such options.

Logs

If you use the GNOME desktop (or other, as Logs can be installed on more than just GNOME), you have at your fingertips a log viewer that mainly just adds the slightest bit of GUI goodness over the log files to create something as simple as it is effective. Once installed (from the standard repositories), open Logs from the desktop menu, and you’ll be treated to an interface (Figure 2) that allows you to select from various types of logs (Important, All, System, Security, and Hardware), as well as select a boot period (from the top center drop-down), and even search through all of the available logs.

Figure 2: The GNOME Logs tool is one of the easiest GUI log viewers you’ll find for Linux.

Logs is a great tool, especially if you’re not looking for too many bells and whistles getting in the way of you viewing crucial log entries, so you can troubleshoot your systems.

KSystemLog

KSystemLog is to KDE what Logs is to GNOME, but with a few more features to add into the mix. Although both make it incredibly simple to view your system log files, only KSystemLog includes colorized log lines, tabbed viewing, copy log lines to the desktop clipboard, built-in capability for sending log messages directly to the system, read detailed information for each log line, and more. KSystemLog views all the same logs found in GNOME Logs, only with a different layout.

From the main window (Figure 3), you can view any of the different log (from System Log, Authentication Log, X.org Log, Journald Log), search the logs, filter by Date, Host, Process, Message, and select log priorities.

Figure 3: The KSystemLog main window.

If you click on the Window menu, you can open a new tab, where you can select a different log/filter combination to view. From that same menu, you can even duplicate the current tab. If you want to manually add a log to a file, do the following:

  1. Open KSystemLog.

  2. Click File > Add Log Entry.

  3. Create your log entry (Figure 4).

  4. Click OK

Figure 4: Creating a manual log entry with KSystemLog.

KSystemLog makes viewing logs in KDE an incredibly easy task.

Logwatch

Logwatch isn’t a fancy GUI tool. Instead, logwatch allows you to set up a logging system that will email you important alerts. You can have those alerts emailed via an SMTP server or you can simply view them on the local machine. Logwatch can be found in the standard repositories for almost every distribution, so installation can be done with a single command, like so:

sudo apt-get install logwatch

Or:

sudo dnf install logwatch

During the installation, you will be required to select the delivery method for alerts (Figure 5). If you opt to go the local mail delivery only, you’ll need to install the mailutils app (so you can view mail locally, via the mail command).

Figure 5: Configuring Logwatch alert sending method.

All Logwatch configurations are handled in a single file. To edit that file, issue the command sudo nano /usr/share/logwatch/default.conf/logwatch.conf. You’ll want to edit the MailTo = option. If you’re viewing this locally, set that to the Linux username you want the logs sent to (such as MailTo = jack). If you are sending these logs to an external email address, you’ll also need to change the MailFrom = option to a legitimate email address. From within that same configuration file, you can also set the detail level and the range of logs to send. Save and close that file.
Once configured, you can send your first mail with a command like:

logwatch --detail Med --mailto ADDRESS --service all --range today
Where ADDRESS is either the local user or an email address.

For more information on using Logwatch, issue the command man logwatch. Read through the manual page to see the different options that can be used with the tool.

Rsyslog

Rsyslog is a convenient way to send remote client logs to a centralized server. Say you have one Linux server you want to use to collect the logs from other Linux servers in your data center. With Rsyslog, this is easily done. Rsyslog has to be installed on all clients and the centralized server (by issuing a command like sudo apt-get install rsyslog). Once installed, create the /etc/rsyslog.d/server.conf file on the centralized server, with the contents:

# Provide UDP syslog reception
$ModLoad imudp
$UDPServerRun 514

# Provide TCP syslog reception
$ModLoad imtcp
$InputTCPServerRun 514

# Use custom filenaming scheme
$template FILENAME,"/var/log/remote/%HOSTNAME%.log"
*.* ?FILENAME

$PreserveFQDN on

Save and close that file. Now, on every client machine, create the file /etc/rsyslog.d/client.conf with the contents:

$PreserveFQDN on
$ActionQueueType LinkedList
$ActionQueueFileName srvrfwd
$ActionResumeRetryCount -1
$ActionQueueSaveOnShutdown on
*.* @@SERVER_IP:514

Where SERVER_IP is the IP address of your centralized server. Save and close that file. Restart rsyslog on all machines with the command:

sudo systemctl restart rsyslog

You can now view the centralized log files with the command (run on the centralized server):

tail -f /var/log/remote/*.log

The tail command allows you to view those files as they are written to, in real time. You should see log entries appear that include the client hostname (Figure 6).

Figure 6: Rsyslog showing entries for a connected client.

Rsyslog is a great tool for creating a single point of entry for viewing the logs of all of your Linux servers.

More where that came from

This article only scratched the surface of the logging tools to be found on the Linux platform. And each of the above tools is capable of more than what is outlined here. However, this overview should give you a place to start your long day’s journey into the Linux log file.

Learn more about Linux through the free “Introduction to Linux” course from The Linux Foundation and edX.

Continuous Security with Kubernetes

By
Julie Dam
-

As the Chief Technologist at Red Hat for the western region, Christian Van Tuin has been architecting solutions for strategic customers and partners for over a decade. He’s lived through the rise of DevOps and containers. And in his role, he’s found that security is the highest adoption barrier for enterprises interested in harnessing the power of containers.

After all, “Now we’re seeing an increasing level of threats for geopolitical reasons, and we’re seeing the dissolving security perimeter,” says Van Tuin. “Everything doesn’t sit behind the firewall in your data center anymore, and there’s a shift to software-based storage, networking and compute. The traditional network base, the fences, are no longer good enough.”

But as he will share during his talk at OpenFinTech Forum in New York City, Oct. 10-11, there are security best practices in the areas of DevOps, containers, and Kubernetes that companies can adopt so that everyone can sleep better at night.

“We’re seeing this evolution to DevSecOps,” he says. “It’s all about reducing security and business risk, lowering costs, speeding up delivery and reaction time, falling in line with DevOps. And we’re doing this with automation process optimization and continuous security improvement.”

This is particularly relevant for FinTech companies. “With the move from physical to digital banking, DevSecOps ensures security is integrated into the process from the start of development rather than appended on in production,” says Van Tuin. “At the same time, it still allows for rapid and frequent releases without security becoming a bottleneck or burden on development.” For instance, OpenSCAP can be used to scan container images for compliance with PCI DSS (Payment Card Industry Security Standard) and customer security policies for banking.

Van Tuin’s best practices are wide-ranging: addressing security risks such as container images, builds, registry, hosts, and network; automating and integrating security vulnerability management and compliance checking in a DevOps CI/CD pipeline; and deployment strategies for container security updates. And he’s hopeful that there will be more improvements to security around Kubernetes with the growth of Istio service mesh and CoreOS operators.

“One of the keys to DevSecOps is to ensure that you can enable your developers to rapidly innovate and experiment,” says Van Tuin. And the first thing that needs to happen? “Embrace security into the culture of the company.”

To hear all about Chris’s strategies for continuous security with DevOps, containers, and Kubernetes, plus talks from other open source leaders, come to OpenFinTech Forum in New York City October 10-11. You can still register here!

Sign up to receive updates on Open FinTech Forum:

​IBM Mainframe Containers Grow More Secure

By
ZDNet
-

Everything old is new again. In the 1960s, IBM’s OS/650 mainframe operating system had two modes, MFT and MVT, in which process got its own address space and couldn’t interface with others processes running parallel with it. This was the ancestor to both virtual machines (VM) and containers. Fast forward to now, and IBM Secure Service Container for IBM Cloud Private enables you to run an operating system and applications in containers with their own address space and walls to keep them from interacting with other programs.

Of course, you can do a wee bit more with Secure Service Containers (SSC) on IBM LinuxONE and Z mainframes than you could on a 360 mainframe with a maximum of 1MB of memory. IBM Cloud Private is a Platform as a Service (PaaS) environment for developing and managing containerized applications. It’s built on top of the Kubernetes container orchestrator Kubernetes.

Read more at ZDNet

14 Common Network Ports You Should Know

By
OpenSource.com
-

The physical ports on your computer allow communicate with peripheral devices such as your keyboard and mouse and to connect with internet devices via Ethernet cables.

Within computer networking, ports serve a similar purpose. When a computer system seeks to connect to another computer, the port serves as a communication endpoint. It is also possible for different services running on the same computer to expose various ports and communicate with one another using these ports. In simple terms, if a software application or service needs to communicate with others, it will expose a port. Ports are identified with positive 16-bit unsigned integers, ranging from 0 to 65535. Other services use this port number to communicate with the service or app. Port numbers are divided into three ranges: well-known ports, registered ports, and dynamic or private ports.

Well-known ports (also known as system ports) are numbered from 0 through 1023. For example, to connect to the host example.com via SSH, I would use this command:

ssh username@example.com -v

In this example, -v stands for verbose,…

Read more at OpenSource.com

1...314315316...10,742Page 315 of 10,742