UNIX Basics

• Table of Contents
• Login / Logout
• UNIX File System
• UNIX File Pathnames
• UNIX Commands

• UNIX®
• a multiuser, multitasking, hierarchical file structure operating system.

Reference: A Practical Guide to UNIX System V, by Mark G. Sobell

• Logging On
• login: pid

Password: __ (Some UNIX systems will initially require the user to establish a password for a new account.)

• The password should be changed by execution of the passwd utility program.
  


• Virtual Terminals
• Multiple terminal emulation exists under UNIX. By executing the X-Windows xterm menu command, (or xterm& from the X-command line), repeatedly, several terminal sessions and programs can be executing simultaneously (alt+ctrl F1-F4).


• Shutting Down
• halt

From the command line, provides checks for maintaining the file system integrity. Wait until prompted to hit any key to reboot before powering down the system.

• Logging Out
• % exit or <Ctrl-D>

UNIX command normally used to end a user's session, but not shut down the machine, closes a terminal session.

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UNIX File System



• Directories (branches) contain either files or subdirectories (branches of branches). Directories are analogous to DOS subdirectories. File system is normally viewed as inverted (upside down) tree.

Highest level directory = root / Users current directory is the "working directory", by default: /home/major/username

• Pathname: filename preceded by directories leading to the file.
• Absolute pathname: the complete pathname of a file starting with the root /.

e.g., /home/major/smith/courses/cs/1044/prog1.c

• Relative pathname: pathname that implicitly starts at the working directory,

e.g., courses/cs/1044/prog1.c

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UNIX File Pathnames



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Special Files
• Every directory contains at least two files: "." and ".."

. is an abbreviation for the current working directory; stores location of current directory. .. is an abbreviation for the directory containing the current working directory (i.e., it's parent); stores location of parent directory.

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UNIX Commands

• Syntax:
  Command [-options] [arguments]

Commands (as filenames) are case sensitive, e.g., "foobar" is not the same as "FooBar". .login or .profile files allow absolute pathnames of commands to be omitted. UNIX commands do not produce messages; by design commands are terse, to allow for piping and redirection (more later).

• [2]% pwd
• Print working directory: displays current working directory path.
• [3]% cd class
• Change directory: alters working directory; used to traverse UNIX hierarchical tree file structure.
• Pathname can be absolute or relative. cd with no arguments returns to home directory. cd .. moves up to parent directory.
• [4]% rmdir p2
• Remove directory: deletes a subdirectory which must be empty.
• [5]% mkdir pascal
• Make directory: creates a directory in the working directory.
• [6]% cat notes
• Concatenate: displays one or more files on the screen.
• [7]% more notes
• More: displays file(s) one screenful at a time, forward or backward through file, and can search for patterns.
• [8]% lpr notes
• Line printer: prints one or more files on the default line printer.
• [9]% ls -aFl
• List: displays files (hidden), following directories with a slash and executable files with asterisks in long form.
• Example:

  total 12
  drwxrwxr-x  6 smith cs1044  480 Dec  6 17:42 .
  drwxrwx--- 26 root  system  816 Dec  6 14:45 ..
  -rw-rw-r--  1 smith cs1044  161 Dec  6 17:15 .profile
  drwxrwxr-x  2 smith cs1044   80 Oct 25 08:33 bin/
  drwxrwxr-x  2 smith cs1044  144 Nov 30 14:25 C/
  -rw-rw-r--  1 smith cs1044  104 Sep 12 19:54 notes
  -rwxrw-r--  1 smith cs1044   85 Jan  4 20:06 run*
  drwxrwxr-x  2 smith cs1044   32 Mar 23 13:45 memos/
  drwxrwxr-x 16 smith cs1044 1296 Dec  6 17:33 shell/
  

ls without a directory argument following the options defaults to the current directory, as do most UNIX commands. ls with file arguments lists information about only those files. Hidden files (.filename) are not displayed without the -a option.

ls output explanation:

• Total line gives the number of blocks in the directory. A block in most UNIX systems = 1/2K (512 bytes), the above directory contains 6K.
• The first character indicates the type of file:

d = directory; - = plain file; l = link

• Characters 2 . . . 10 give the file access permissions:

r = read; w = write; x = execute.

• Characters 2, 3, 4 give the owner's permissions, followed by group and other user's permissions. A - denotes absence of the permission.
• Number of links to the file.
• File owner's name.
• Group name for the file.
• Size of the file in bytes (characters).
• File creation or modification date and time, and the name of the file.

Last modified: Mon Sep 1 22:27:17 EDT 1997