Linux Note 1 20160714

Some explaining: as I am using ubuntu(linux, English version), what the fuck thing is that I don't know how to type in Chinese by pinyin.So these days I have to keep learning linux until I know how to change the current situation. So what you see now will only be English. Fast may I learn!
```
# orders
```
application_name # run it
application_name & #run it in the backyard
sleep 5000 # sleep for 5000 seconds
ctrl + c #can terminate the process above
ctrl + z #pause
bg code # let the process in the backyard run
fg code # put the process in the front yard(of course it will run)
```
# Basic file system structure of Linux
path is divided by '/'
## current working index
```
pwd #print work directory
touch file_name #create a new file or update the exiting file's time
#if a file's name begin with . , it will get hided.
```
```
ls #show the directory's files
ls -a #show all the files including the hidden ones(most of the hidden files are setting files)
ls -l # detailed information
ls -R #show the file index in the son files
ls file_name #
ls -ld file_name 
file file_name # what kind of the file is
```
### absolute path & relative path
absolute path: begin with '/' to the target
relative path: from the current path to the target path
```
cd +
. #current index
.. # the upper index
- # return the last index
~ # the user's home index
Enter #back home
```