https://www.tecmint.com/free-online-linux-learning-guide-for-beginners/
http://www.linux-tutorial.info/
https://linuxconfig.org/linux-tutorials
http://heather.cs.ucdavis.edu/~matloff/unix.html
https://www.howtoforge.com/
http://www.thegeekstuff.com/2010/12/50-unix-linux-sysadmin-tutorials/?utm_source=feedburner
http://www.sanfoundry.com/1000-linux-command-tutorials/
http://www.freeos.com/guides/lsst/
http://kalilinuxtutorials.com/
https://www.shellscript.sh/
http://www.linuxplanet.com/tutorials
https://hackr.io/tutorials/learn-system-administration
http://landoflinux.com/
http://www.kalitut.com/
https://www.linuxtechi.com/
http://freelinuxtutorials.com/
http://searchdatacenter.techtarget.com/tutorial/77-Linux-commands-and-utilities-youll-actually-use
http://www.omnisecu.com/gnu-linux/index.php