new page, 'Linux File Permissions', and corresponding screenshots

content/guides/running_applications/linux_file_permissions.md

++++
+title = "Linux File Permissions"
+description = "How to view and change file permissions with Linux commands"
+weight = 20
++++
+
+- [Opening a Terminal Window] (#opening-a-terminal-window)
+- [Listing File Permissions] (#listing-file-permissions)
+- [Changing File Permissions] (#changing-file-permissions)
+
+## Opening a Terminal Window
+-----------------------
+
+Use your local terminal to connect to a cluster, or open a new terminal window on [Crane](https://crane.unl.edu). 
+
+Click [here](https://hcc.unl.edu/docs/quickstarts/connecting/) if you need help connecting to a cluster 
+with a local terminal.
+	
+Click [here](https://hcc.unl.edu/docs/guides/running_applications/jupyter/) if you need 
+help opening a new terminal window within JupyterHub.
+
+## Listing File Permissions
+
+Type the command `ls -l` to list the files and directories with file permissions for your current location.
+
+{{< figure src="/images/LinuxList.png" >}}  
+
+The first character denotes whether an item is a file or a directory. If 'd' is shown, it's a directory, and if '-' is shown, it's a file.
+ Following the first character you will see some 
+combination of r,w,x, and -. The first rwx is the ‘read’ ‘write’ ‘execute’ file permissions for the creator
+ of that file or directory. A ‘-‘ instead means a particular permission has not been granted. For example “rw-“ means the 
+ ‘execute’ permission has not been granted. The next three entries are the permissions for ‘group’ and the last three are the 
+ permissions for everyone else.
+ 
+ Following the file permissions are the name of the creator, the name of the group, the size of the file, the date it was created, and finally 
+the name of the file.
+
+
+## Changing File Permissions
+
+To change file permissions, use the command "chmod [permissions] [filename]" where permissions are indicated by a three-digit code.
+Each digit in the code correspondes to the three digits mentioned above in the permissions printout: One for the creater permissions, 
+one for the group permissions, and one for everyone else. The command is interpreted as follows: 4=read 2=write 1=execute and any combination of these is given by summing their codes.
+Each chmod command will include 3 codes.
+For example, to give the creator of mars.txt rights to read, write and execute, the group rights to read and execute, and everone else only the right to read,
+we would use the command `chmod 754 mars.txt`
+
+{{< figure src="/images/LinuxChange.png" >}}