MacOS Sierra HowTo - Linux / Unix Q & A from nixCraft

Windows like Ctrl + Alt + Delete on MacOS App To Kill Tasks

in Mac OS X, UNIX last updated May 24, 2017

On Windows, I can hit Ctrl + Alt + Delete and kill apps or do other stuff. Sometimes Firefox browser hangs on macOS. Is there an equivalent of Ctrl + Alt + Delete keyboard shortcut to kill frozen apps on Apple macOS Sierra?

How to copy a single file to multiple directories in Linux or Unix

in BASH Shell, CentOS, Debian / Ubuntu, FreeBSD, Linux, RedHat and Friends, Suse, Ubuntu Linux, UNIX last updated January 17, 2017

If I want to copy a single file into three locations (directories), by using a single cp command (e.g. cp file /dir1/ /dir2/ /dir3/. Would that be possible? If yes, please provide the command for GNU/Linux or Unix operating systems.

How to fix: MacOS keep asking passphrase for ssh key after upgrade or reboots

in Mac OS X, OpenBSD, UNIX last updated January 17, 2017

I recently upgraded my MacOS Sierra and now ssh command keep asking for passphrase as follows when I try to login to my remote Linux/Unix server:
Enter passphrase for key ‘/Users/vivek/.ssh/id_ed25519’:
How do I fix MacOS Sierra upgrade that keep breaking ssh keys in terminal?

Mac OS X Sierra Install wget Network Downloader Utility

in BASH Shell, Commands, Mac OS X, UNIX last updated April 1, 2017

I recently learned that “wget” can continue getting a partially-downloaded (resume download) file. I am unable to find wget command on Mac OS X. How do I install install wget on Mac OS X (Mountain Lion/ Mavericks / Snow Leopard)? How can I install wget in Mac OS X without 3rd-party repo such as Homebrew or MacPorts?