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Unix Filesystem

Unix Filesystem. January 26 th , 2004 Class Meeting 2. * Notes adapted by Christian Allgood from previous work by other members of the CS faculty at Virginia Tech. Unix Filesystem. The filesystem is your interface to: physical storage (disks) on your machine storage on other machines

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Unix Filesystem

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  1. Unix Filesystem January 26th, 2004 Class Meeting 2 * Notes adapted by Christian Allgood from previous work by other members of the CS faculty at Virginia Tech

  2. Unix Filesystem • The filesystem is your interface to: • physical storage (disks) on your machine • storage on other machines • output devices • Everything in Unix is a file (programs, textfiles, peripheral devices, terminals) • There are no drive letters in Unix – the filesystem is a logical view of the storage devices

  3. Working Directory • Working Directory – the current directory in which you are located • pwd (print working directory) command outputs the absolute path (more later) of your working directory • Unless you specify another directory, commands will assume that you want to operate on the working directory

  4. Home Directory • Directory for users to store personal files • At login, your working directory will be set to your home directory • The path (more later) to your home directory can be referred to by the ~ (tilde) symbol • The home directory of “user1” is represented by ~user1

  5. Unix File Hierarchy • Root Directory: / • Directories may contain plain files or other directories • Result is a tree structure for the filesystem • Unix does not recognize any special filename extensions / bin home etc user1 user2 textfile cs2204 lab1txt lab2txt

  6. Unix Paths • Separate directories by / • Absolute Path • start at root and follow the tree • Example: • /home/user1/textfile • ~users1/textfile • ~/textfile / bin home etc user1 user2 textfile cs2204 lab1txt lab2txt

  7. Unix Paths (cont) • Relative Path • start at working directory • . . – level above • . – working directory / bin home etc user1 user2 textfile cs2204 lab1txt lab2txt

  8. Some Standard Directories • / - root directory • /bin – standard commands and utilities • /dev – block and character device directory • /etc – host-specific configuration files and directories • /home – users directory • /lib – library directory • /sbin – system commands and utilities (needed to boot) • /tmp – temporary files • /usr – most user utilities and applications • /var – files that vary as the system runs (logs, spools)

  9. Changing Directories • cd – changes the working directory • cd <directory_path> • can use absolute or relative path names • cd without any arguments is the same as: cd ~ • Examples: • cd /home/user1 • cd ../../user1

  10. Output of ls -lF lrwxrwxrwx 1 callgood Grads 20 Jan 24 20:16 home -> /home/grads/callgood/ -rw-r--r-- 1 callgood Grads 392419 Sep 22 10:07 atoll.jpg drwxr--r-- 2 callgood Grads 64 Jan 24 18:33 cs2204/ • We’ll keep coming back to this slide permissions user group modified date filename file type size

  11. Types of Files • Plain ( - ) • Most files, binary or text • Directory ( d ) • Directory is actually a file • Points to another set of files • Link ( l ) • Pointer to another file or directory • Special • b – block device (disks, CD-ROM) • c – character device (keyboard, joystick)

  12. Manipulating Files • touch <file> • create a new file or change last modified date • mv <file1> <file2> • rename file1 as file2 • mv <file1> <dir> • move file1 into the dir directory • mv <file1> <dir/file2> • move file1 into dir and rename as file2 • cp <file1> [<file2>|<dir>|<dir/file2>] • copy file with new name, into directory, or both • rm [-i] <file(s)> • remove file or list of files

  13. Creating and Removing Directories • mkdir <directory_name> • create a subdirectory of the current directory • rmdir <directory_name> • remove directory • only works for empty directories • rm -r <directory_name> • remove directory and all of its contents, including subdirectories

  14. Creating Links • ln -s <existing_file> <link_name> • creates a symbolic link • link_name will be a pointer to existing_file which may be in another directory or even on another physical machine

  15. File Ownership • Each file has a single owner • chown command can be used to change the owner; usually only root user can use this command • Users can also belong to various groups • Groups may have different permissions than everyone else

  16. File Permissions • Permissions are used to allow or disallow access to files or directories • Three types of permission: • Read ( r ) • Write ( w ) • Execute ( x ) • Permission exists on three levels: • User ( u ) • Group ( g ) • World ( o )

  17. File Permissions (cont) • chmod <mode> <file(s)> • chmod 700 textfile • chmod g+rw textfile r w xuser r w xgroup r w xworld ugo +/- rwx

  18. File Modification Date • Last time a file was changed • Useful when . . . • there are many copies of a file • many users are working on a file • touch command can be used to update the modification date to the current date (or to create a file if it doesn’t exist)

  19. Looking at File Contents • cat <filename(s)> • short for concatenate • output the contents of the file all at once • more <filename(s)> • output the contents of the file one screen at a time • allows forward and backward search

  20. Getting Help on Unix Commands • man <command_name> • shows all of the documentation for a command (more-style output) • apropos <keyword> • shows you all of the commands with the specified keyword in their description

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