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As of the latest CentOS 7, the default Python version still remains python 2.7, and python3 is not available in base repositories. If you need to use python3 as part of Python application dependency, there are several ways to install python3 on CentOS.

When you want to create a new server which has exactly the same set up as any existing server X, you need to find out what packages have been installed on server X. Also when you are trying to migrate your old Linux system to to a freshly installed newer OS release, you need to keep track of previously installed package list. In other times, you may just want to know what packages you installed from a specific third-party repository.

GNOME Keyring is a daemon program which caches user's secret keys, login credentials and certificates, and makes them available to other applications requesting them according to the GnuPG protocol. Essentially GNOME Keyring plays the same role as gpg-agent, but is active only within GUI desktop sessions. GNOME Keyring also implements SSH agent protocol for SSH authentication to replace ssh-agent.

When the Python interpreter executes a program which imports a module, it examines all directory paths listed in sys.path until it finds the module. By default, sys.path is constructed as a concatenation of (1) the current working directory, (2) content of PYTHONPATH environment variable, and (3) a set of default paths supplied by the installed Python interpreter.

Originally based on BSD RCP protocol, SCP (Secure copy) is a mechanism that allows you to transfer a file between two end points over a secure SSH connection. However, as a simple secure copy protocol, SCP does not understand range-request or partial transfer like HTTP does.

When you are writing code for your program, you must understand that there are standard coding styles to follow. For example, "trailing whitespaces" are typically considered evil because when they get into a code repository for revision control, they can cause a lot of problems and confusion (e.g., "false diffs").

Amazon AWS security credentials are used to authenticate you and authorize any third-party application to access your AWS account. There are different types of AWS security credentials available, e.g., password, access key, multi-factor authentication, X.509 certificates, etc.

Many Java programs or Java-based IDE environments require JAVA_HOME environment variable being set. This environment variable is supposed to point to the top directory where the Java development kit (JDK) or Java runtime environment (JRE) is installed. The JDK contains everything the JRE offers, but also provides additional binaries and libraries needed to compile Java programs.

There are different ways to tell what shell you are currently in. The easiest way to find that out is by using special shell parameters. For one, a special parameter named "$$" denotes the PID of the current instance of the shell you are running. This parameter is read-only and cannot be modified.

When a Java program is built, the build environment sets a "target" which is the oldest JRE version the program can support. If you run the Java program on a Linux system which does not meet the lowest JRE version requirement, you will encounter the following error while starting the program.

Unlike Ubuntu server, installation of Ubuntu desktop is pretty much auto-pilot, not leaving much room for customization, such as custom disk partitioning, manual network settings, package selection, etc. While such simple, one-shot installation is considered user-friendly, it leaves much to be desired for those users looking for "advanced installation mode" to customize their Ubuntu desktop installation.

In multi-user Linux environment, it's a standard practice to create user accounts with some random default password. Then after a successful login, a new user can change the default password to his or her own. For security reasons, it is often recommended to "force" users to change the default password after the first login to make sure that the initial one-time password is no longer used.

The modern Linux kernel has been growing significantly over the years to support a wide variety of hardware devices, file systems or networking functions. During this time, "loadable kernel modules (LKM)" came into being in order to keep the kernel from being bloated, while flexibly extending its capabilities and hardware support under different environments, without having to rebuild it.

When you run a process that wants to read or write to a USB device, the user/group of the process must have appropriate permission to do so. Of course you can change the permission of your USB device manually with chmod command, but such manual permission change will be temporary. The USB device will revert to its default permission mode when you reboot your Linux machine.

When you run performance-critical HPC applications or network-heavy workload on multi-core NUMA processors, CPU/memory affinity is one important factor to consider to maximize their performance. Scheduling closely related processes on the same NUMA node can reduce slow remote memory access.

In Ubuntu environment, there are several ways for the kernel to get upgraded. On Ubuntu desktop, Software Updater allows you to check for and update to the latest kernel on a daily basis. On Ubuntu server, the unattended-upgrades package takes care of upgrading the kernel automatically as part of important security updates.

For Linux desktop users, there are many ways to access weather forecasts, e.g., using standalone weather apps, desktop widgets, or panel applets. If your work environment is terminal-based, there are also several ways to access weather forecasts from the command line.

I have an application running, which forks a number of threads at run-time. I want to know how many threads are actively running in the program. What is the easiest way to check the thread count of a process on Linux?

Open vSwitch (OVS) is the most popular open-source implementation of virtual switch on the Linux platform. As the today's data centers increasingly rely on the software-defined network (SDN) architecture, OVS is fastly adopted as the de-facto standard network element in data center's SDN deployments.

Wine was developed as compatibility layer software for Linux, which allows you to run Microsoft Windows applications on Linux and other UNIX-based operating systems (OS X, FreeBSD, Solaris). Wine achieves this by implementing compatible Windows application binary interfaces. PlayOnLinux is a graphical frontend for Wine.