Freq used Linux commands:
File system:
List files/dirs: ls (long: -l human-readable: -h dir itself: -d)
File system space usage: df (-h)
View file content: cat
Create empty file/update file timestamp: touch
Create dir: mkdir (-p)
Remove(delete) file/dir: rm (-rf), rmdir
Copy file : cp (-r)
Change dir: cd (..,~, -, "")
Current dir: pwd
Trace file change: tail -F
Find in files: grep (-iname, -mtime, -mmin, -exec)
Change file mode (rwx): chmod
Change file owner: chown
Software management:
dpkg/apt (Ubuntu)
yum (REL/CentOS)
Command/process:
What is this command? which/type
Put process in background/foreground: &, bg, fg
User management:
who, whoami, w, id, useradd/userdel
Misc:
Looking for help: man ("man 5 crontab" for help on files)

Editor
gedit
nano
vim
Dev environment:
java
mysql
     GUI: sqlyog
mongo
     GUI: robomongo
git
     GUI:gitk
Resources:
免费linux体验环境 http://linuxlearn.net