Linux commands

lsof 

http://ehaselwanter.com/en/blog/2009/03/13/tomcat-too-many-open-files/

http://alvinalexander.com/blog/post/linux-unix/linux-lsof-command

http://www.thegeekstuff.com/2012/08/lsof-command-examples/

http://unix.stackexchange.com/questions/163351/how-to-find-the-process-with-maximum-file-descriptors

http://www.cyberciti.biz/tips/linux-procfs-file-descriptors.html

 

grep 

http://www.cyberciti.biz/faq/howto-use-grep-command-in-linux-unix/

http://www.computerhope.com/unix/ugrep.htm

http://www.tutorialspoint.com/unix_commands/grep.htm

 

sudo

http://www.howtogeek.com/111479/htg-explains-whats-the-difference-between-sudo-su/

https://www.linux.com/blog/how-use-sudo-and-su-commands-linux-introduction

https://en.wikipedia.org/wiki/Sudo

https://linuxacademy.com/blog/linux/linux-commands-for-beginners-sudo/

http://www.computerhope.com/unix/sudo.htm

http://www.tutorialspoint.com/unix_commands/sudo.htm

http://www.tecmint.com/su-vs-sudo-and-how-to-configure-sudo-in-linux/

 

Unix commands

https://www.tutorialspoint.com/unix/index.htm