Filesystem

Boiled down:

Everything is a File

• Linux has a hierarchical file system with access controls for the user, group, and all others
• A file is a sequence of characters (or bytes)
• The size of the file is not stored in the file
• The name of the file is not stored in the file
• The is no end-of-file (EOF) marker in the file
• There are ordinary, directory & device files
• text files vs Binary files
• Text files
  Contain plain text as typed at the keyboard
  Basic separator is the newline (LF char)
  Uses with cat, more,(less a superset of more with vi commands), vi, pico etc
• Binary files:
  Contain characters not .on the keyboard. and that can.t be displayed on the screen
  Created by a compiler (or even MS Word)

Directories vs. Files

• Directories
  a file representation of the disk structure
  Can't be directly modified by the user . the shell does this for you
  User can view "it"s contents. using ls
  It is a representation of (part of) the file structure
  Contains filename & indode #
  Inode is the data structure that contains files attributes, disk block location(s), etc
• Device Files
  A file system representation of each linux device
  You can read from a device (file)
  You can write to a device (file)
  But it is actually empty. it provides a consistent way to address all devices by representing them as files

Hierarchical File System

• Absolute path names
• Relative path names
. and ..
• $PATH
  What is searched and in what order?
  Is the current working directory (pwd) part of the path?
• $HOME
  $HOME is the shell (environment) variable that keeps track of your home directory.
  Like an absolute web address, you should never "hard code" your home directory. it might move
• pwd is very useful when starting with linux
  - Keep track of your current working directory
  - Used in scripts
• cd we will use directories for organization, but also as places for project separation

Filenames

• Letters, digits, -, period, comma
• 255 characters was old limit
• Hidden files
  Common for "start up" files
  In Linux a hidden file is not displayed in response to a normal listing (ls)
• File Commands
  • make a directory - mkdir
  • Change to a directory - cd
  • List files in a directory - ls (See page 70 for options to ls)
  • Display working directory - pwd
  • Remove a directory - rmdir
  • File Copy - cp source destination (-R for recursive)
  • Move file - mv source destination
  • Print file - lpr filename
  • wc - count lines word and characters in file
  • od -bc
  • tar -cvf archive.tar file_list (-x extracts, -t displays)
  • gzip list of files (creates .gz file_
  • unzip filename.zip

Typical Unix directories

• /etc
• /var
• /usr
• /tmp
you should know /tmp where you (anyone) may create temporary files
• /sys
• cd without any parameters takes you to home directroy (echo $HOME)

All work herein is subject to copyright. Original content to Dr. Deborah Whitfield, text content (Practical Guide to Linux) to Prentice Hall publishing.