Introduction to UNIX and SFTP

Transcription

1 Introduction to UNIX and SFTP

2 Introduction to UNIX 1. What is it? 2. Philosophy and issues 3. Using UNIX 4. Files & folder structure

3 1. What is UNIX? UNIX is an Operating System (OS) All computers require an OS The OS is a program that effectively controls a computer s resources Memory Hard drive and files Peripherals Among other things, the OS allows you to launch programs, save files, and communicate with other computers

4 What is UNIX, cont d UNIX comes in many flavours and typically runs on larger, multi-user machines, or on the machines of the technically savvy Our Sun machines run SunOS and Solaris Mac OS X runs BSD Unix Many of our PCs run Linux UNIX is common on Internet-based machines You should already have an ACN UNIX account

5 2. Open Source/Free Software Which is better, Linux or Windows? Should we have to pay for an OS? Is it really the Microsoft Tax? What are the advantages/disadvantages of letting everyone have access to an OS s source code? Should you use Linux?

6 3. Using UNIX Recall that in COMP 1260, you used claimid to claim your U of M mail account This is also your UNIX account Many of the computers that run UNIX on campus are behind locked doors You can still use them; you don t need a key, just your password and a communications client

7 Connecting with telnet telnet is a communications client Available on some Microsoft Windows platforms Acts as a client for a corresponding server on another (remote) computer Your computer Remote computer Telnet client (running a telnet server)

8 A Problem with telnet Telnet uses the Internet to communicate with the remote computer The protocols that are used on the Internet are very good at providing robust, flexible communication They do not provide secure communication, though Telnet sends its packets in clear text form This means that information you type into telnet (like userid s and passwords) is vulnerable to being intercepted by someone with malicious intent We want a communications client that encrypts (scrambles) our communications

9 SSH Short for Secure Shell It is a communications client that encrypts its information If someone intercepts the packets, the information will just be gibberish SSH Secure Shell for Workstations (and Windows) is available at Software Express It also contains a secure FTP client

10 Using SSH client Choose File Connect Enter Host Name and UMnetID you get another dialog for your password You can save this info as a Profile so you don t need to type it

11 With OS X on a Macintosh Use Terminal (in Utilities) To connect, at the prompt enter ssh -l UMnetID Host You will be prompted for your password

12 Another Option SSH is a text-only program You type text commands, you get text responses Recall from COMP 1260: there are graphical user interfaces to UNIX Many are based on X (or X-Windows) There are X terminals in the labs, and X programs available on Software Express

13 After Connecting OK, I can get in. Now what? Regardless of whether you are using X or SSH, you will have a window where UNIX commands can be executed This command line will have a prompt such as pollux% or mira% This is where you enter UNIX commands and launch programs (more later!) Your UNIX account will potentially allow you to do many things. In this class we will use it to host our personal web pages.

14 4. Files and Folder Structure The UNIX environment Among other things, your UNIX account is used to store directories and files A UNIX directory is similar to a Windows folder Files consist of documents, applications, and data ~ file1 dir1 file2 dir2 file1 file2

15 UNIX Every UNIX directory and file can be identified by a unique path name ~/file1 ~/dir1/file1 ~/dir1/dir2/... ~ file1 dir1 file2 dir2 file1 file2

16 UNIX The tilde (~) represents your home directory Every UNIX user has their own home Name matches user id At the top of the hierarchy is the root directory represented by / / u1 u2 u3 umable umbaker umchan

17 UNIX This means that all your files are on the same computer (same hard drive) as everybody else s For privacy s sake, files have permissions Can decide whether or not they are accessible to others

18 UNIX When permissions allow, it is possible to access files in another user s home directory You don t have to know exactly where; shortcut: ~umchan/file2 / u1 u2 u3 umable umbaker umchan file2

19 UNIX Making files available on the web will require a directory known as public_html under your home directory An HTML file in there called index.html will be the starting point (home page) of your site ~ public_html index.html another.html some_dir

20 UNIX Exercise: name the paths to all 6 files in the following diagram ~ dir1 dir2 file1 file2 dir3 file3 dir4 file4 file5 file6

21 File Types and File Transferring 1. File types 1. Platform Dependence (ASCII vs binary) 2. Transferring files between platforms 3. SFTP 1. Uploading 2. Auto Select 3. Changing permissions

22 1. File types There are many types of files on a computer Executable (application) files Documents created by applications (word processor, graphics, sound, video, etc.) OS files Library files (dll s) Text files (txt, html, ps) Most of them are meant to be read by the computer or a program these are referred to as binary files Text files are meant to be read by humans

23 File Types Application Text Editor ASCII Table

24 Representing bytes All files consist of a series of bytes Recall a byte consists of 8 binary digits (bits) A byte is usually represented using hexadecimal (hex) digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F Each one represents 4 bits, so a byte is represented by 2 hex digits Writing hex is often easier than writing binary e.g = 5C

25 Interpreting bytes Since all files are just a series of bytes, what is the difference between binary and text files? All files are made up of bytes In a sense, all files are binary It s in the way they are interpreted An application is interpreted as a series of machine instructions An MS Word document is interpreted as a description of the document s contents A text file is interpreted as a sequence of characters (typically ones from a keyboard)

26 ASCII In order to interpret bytes as characters, we use a code that maps bytes to characters The ASCII (American Standard Code for Information Interchange) code is the most common e.g. some characters and ASCII codes (in hex) 0 (30), 1 (31), 9 (39) A (41), B (42), Z (5A) a (61), b (62), z (7A)! (21),? (3F), ( (28), ) (29), { (7B), (7C)

27 Collating sequence The ASCII codes form a collating sequence that is used to sort text alphabetically 1. We compare two strings byte by byte 2. When we find 2 bytes that are different, the text string with the smaller byte is first alphabetically 3. a string formed by adding to the end of another string appears later alphabetically e.g. cat < dog (63 < 64) see Spot < see spot (53 < 73) Gord < Gordy (rule 3)

28 Whitespace Some ASCII codes represent whitespace Characters that aren t visible but control the layout of the text e.g. Tab (09), Space (20), Backspace (08), CR (carriage return go to beginning of line) (0D), NL (new line move down a line) (0A), NP (new page) (0C) In Unix, man ascii will give a table of all the ASCII codes ASCII tables are available on the web (see last slide)

29 Text editors A text editor like Notepad allows us to type text and store it as a sequence of ASCII bytes When we open a text file, the editor interprets the bytes as ASCII characters Binary files can be opened in a text editor, but the result would be mostly gibberish most of the bytes aren t aren t likely meant to be interpreted as characters

30 Typing in a text editor What happens when we type the following into a text editor? Hello Goodbye What is the sequence of bytes stored in the text file? Hello = C 6C 6F Goodbye = 47 6F 6F What about?

31 Platform dependence Unfortunately, different computers deal with Enter in different ways When you type Enter, it is stored differently DOS/Windows C 6C 6F 0D 0A 47 6F 6F D 0A Mac UNIX C 6C 6F 0D 47 6F 6F D C 6C 6F 0A 47 6F 6F A

32 2. Transferring files Platform dependence is a problem when we want to transfer files between computers Binary files can be transferred without change Text files created on one platform cannot be transferred to another platform without changes

33 Transferring files The Internet is used to transfer millions of files every day both binary and text We don t worry about platform dependence when using a browser because it performs the conversion of text files automatically We will use Secure File Transfer Protocol (SFTP) to transfer files from our computer to a remote computer

34 3. SFTP SFTP is a secure Internet client used to transfer files between computers It is aware of the platform dependence of text files and performs the conversion for us when we transfer text files. We just have to tell it what sort of transfer to use for a particular file Binary transfer the bytes unchanged ASCII substitute the correct character(s)

35 SFTP Terms SFTP transfers files between a local computer and a remote computer An SFTP client runs on the local computer It communicates with an SFTP server on the remote computer Remote computer sometimes called a host SFTP has two transfer modes Binary and ASCII (text) Transfers to the local computer are called downloads Transfers to the remote computer are called uploads

36 Secure File Transfer Client Connect to a host just like SSH Save as a profile Client has 2 file navigation windows left is for local computer right is for remote computer

37 SFTP with OS X on a Macintosh Use FileZilla (available from Software Express) or TextWrangler for text or html files File / Open from FTP/SFTP Server (downloads file from server) File / Save to FTP/SFTP Server (uploads file to server) File / Save a copy to FTP/SFTP Server (uploads a copy of the file to server)

38 Transferring files and folders Drag and drop from one window to the other The bottom window shows the status of the transfer

39 Auto Select Secure File Transfer Client can automatically choose between binary and ASCII transfer mode Based on a file s extension Edit Settings File Transfer - Mode Add extensions (e.g..txt) to the list Any file with an extension from the list will be transferred in ASCII mode All others are transferred in binary mode Be sure to choose Auto Select from the toolbar

40 Using SFTP You ll likely develop your web pages on a PC and transfer them when they re ready for publication We can use Secure File Transfer Client to create a public_html directory and transfer our web site to our Unix account Connect to ccu.umanitoba.ca (with your UMnetID) Tell the client to create public_html in your home directory Copy index.html and your other files into public_html

41 File Permissions with SFTP By default, no one can access your web page Recall that we have to make our files readable You can use Secure File Transfer Client to change the file permissions. right click on the file or folder and choose Properties (more on this later)

42 File naming conventions Windows and Unix differ in their rules for naming files Windows file names are case insensitive e.g. index.html and Index.HTML are the same Unix file names are case sensitive e.g. index.html and Index.HTML are different Windows file names may contain blanks Unix file names may not contain blanks

43 File naming conventions Some older Windows applications may be case destructive i.e. file names are converted to uppercase Keep these differences in mind when constructing a web site offline Otherwise, a web site that works fine on your Windows computer may be broken when uploaded to a Unix web server

44 File naming conventions File naming conventions for a web site that will be uploaded to a Unix server: lowercase letters (a z) digits (0 9) dash (-) and underscore (_) NO BLANKS!