Applied Math Website

Basic Unix

``Hey, it's Unix! I know this!'' - Lex, Jurassic Park	Many of us folks who actually work with Unix a lot rolled our eyes at this point in the movie. Lex was using a mouse to move around and click on graphical images on the computer screen, none of which seemed to require any acquaintance with Unix. In general, Unix computers may not have as good a graphical interface (windows, menus, folders, icons, etc.) as a Macintosh computer. But that's OK. We still tend to do different things on the Unix workstations than we would on a Mac/PC. Many times it's easier, or just as easy, to type a command as to fiddle with mouse/windows/menus. (Lines of distinction are becoming blurred -- new Macs actually are based on Unix, while the graphical interface of newer Linux versions are feeling more like other familiar systems -- and both can emulate Windows.) Anyway, the real strengths of Unix lie elsewhere.

``Hey, it's Unix! I know this!''
- Lex, Jurassic Park

Many of us folks who actually work with Unix a lot rolled our eyes at this point in the movie. Lex was using a mouse to move around and click on graphical images on the computer screen, none of which seemed to require any acquaintance with Unix.

In general, Unix computers may not have as good a graphical interface (windows, menus, folders, icons, etc.) as a Macintosh computer. But that's OK. We still tend to do different things on the Unix workstations than we would on a Mac/PC. Many times it's easier, or just as easy, to type a command as to fiddle with mouse/windows/menus. (Lines of distinction are becoming blurred -- new Macs actually are based on Unix, while the graphical interface of newer Linux versions are feeling more like other familiar systems -- and both can emulate Windows.)

Anyway, the real strengths of Unix lie elsewhere.

Unix is designed to run dozens of processes, and handle multiple users, simultaneously on a single computer. If one process (program) crashes, it doesn't freeze or crash the whole computer. Generally our workstations can run continuously for months, although the administrator may reboot a workstation for reasons of his own :-)
Your files are available on any of the 20+ workstations in our LAN, day and night, requiring only your login password. You can access (log on, type Unix commands on) these workstations via the internet from anywhere in the world, using ssh.
You can control exactly which of your files or directories are readable and/or writeable by others
The workstations have the most important computational software, like Mathematica, Matlab, and compilers for Fortran and C. You can run large numbercrunching jobs in the background -- that is, start the job, log off and go home, and let the computation continue even while others use the computer
All our files are stored centrally and backed up nightly. There is disk space for dozens of gigabytes of files on our systems, and each workstation in the Newton Lab has at least 256 Mb of RAM.
The Newton Lab is usually better maintained and less crowded than the public Mac/PC labs

	The sometimes mysterious-looking typed Unix commands are the core of this workshop. Usually there are several versions of a command, and you must read the manual page for that command to understand them. While the Unix commands may be weird, they are at least short (usually 2-4 letters long) for quick typing, and have at least some mnemonic content. Most of the commands are about manipulating files and directories; creating, naming, moving, deleting, reading. Plain text files (``ASCII files'') get the most attention; there are commands for editing, spellchecking, wordcounting, compiling, displaying, printing, and filtering.

The sometimes mysterious-looking typed Unix commands are the core of this workshop. Usually there are several versions of a command, and you must read the manual page for that command to understand them.

While the Unix commands may be weird, they are at least short (usually 2-4 letters long) for quick typing, and have at least *some* mnemonic content.

Most of the commands are about manipulating files and directories; creating, naming, moving, deleting, reading. Plain text files (``ASCII files'') get the most attention; there are commands for editing, spellchecking, wordcounting, compiling, displaying, printing, and filtering.

the directory tree -- how things are arranged, how to move around and know where you are
about file names -- Unix is case-sensitive, and touchy about punctuation
creating and renaming and copying and deleting files and directories
editing text files -- there is vi, and the rest
other commands for text files -- displaying, filtering, and other tricks
help with spelling -- spell and look
special kinds of files

The power of the basic Unix commands increases tenfold when combined with the succinct Unix syntax. The output from one command can be directed into a new file, or appended to an existing file, or passed along as input to another command. Wildcard characters let you specify multiple files. The semicolon separates multiple commands on a single line, and you can define your own simple aliases for often-used long Unix commands, in the special file .cshrc (located in your home directory). Also in .cshrc is the definition of your ``search path'' and other important system variables.

	The power of the basic Unix commands increases tenfold when combined with the succinct Unix syntax. The output from one command can be directed into a new file, or appended to an existing file, or passed along as input to another command. Wildcard characters let you specify multiple files. The semicolon separates multiple commands on a single line, and you can define your own simple aliases for often-used long Unix commands, in the special file `.cshrc` (located in your home directory). Also in `.cshrc` is the definition of your ``search path'' and other important system variables.

redirecting output into a file or into another program
JOB CONTROL -- juggling multiple processes
the secrets of your .cshrc and .login files, including aliases
the file .ssh/known_hosts

	Traditionally, you could connect to other computers using telnet and rlogin and (for transferring files from one computer to another) ftp. All three programs, however, are insecure; crackers (malicious hackers) can and do have programs that can intercept network traffic -- including passwords -- which then enables them to log on to computers and do malicious hacking in somebody else's name. The Applied Math computers, like most computers on campus, have been hacked into now and then, which is why we now disallow (or at least discourage) the use of telnet & rlogin & ftp. Instead, secure versions are available: ssh and scp. These replace telnet and ftp, respectively, and cleverly encrypt/decrypt outgoing and incoming communications so that any hacker's ``sniffer program'' will hear only gibberish. Examples of usage:

Traditionally, you could connect to other computers using telnet and rlogin and (for transferring files from one computer to another) ftp. All three programs, however, are insecure; crackers (malicious hackers) can and do have programs that can intercept network traffic -- including passwords -- which then enables them to log on to computers and do malicious hacking in somebody else's name.

The Applied Math computers, like most computers on campus, have been hacked into now and then, which is why we now disallow (or at least discourage) the use of telnet & rlogin & ftp. Instead, secure versions are available: ssh and scp. These replace telnet and ftp, respectively, and cleverly encrypt/decrypt outgoing and incoming communications so that any hacker's ``sniffer program'' will hear only gibberish. Examples of usage:

ssh newton.colorado.edu log on securely to the workstation newton
scp data.html amath: copy (securely) the file ``data.html'' into my home directory on workstation amath
scp amath:/www/courses/2360/data.html ./datfile copy (securely) the named file on amath to this computer, in the current directory, as file ``datfile''

	You may maintain personal web pages in your account on ucsu, or on the Applied Math department's web server amath, or on both. Or, you may need to maintain web pages on amath for an Applied Math course. For any Applied Math web pages, personal or course-related, you can either

ssh amath and edit HTML files directly on amath, or
create a web page (HTML file) by other means (e.g., using Netscape, StarOffice, or Word) and then copying it to amath using scp

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Basic Unix

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Unix syntax and special files

basic Unix commands