File System Structure

1
File System Structure

• Directory Structure
• Navigation
• -Absolute
• -Relative
• Access Permission
• -chmod
• -umask

2
File Naming Rules

• What can be used for naming files in Unix are
• -letters (uppercase, lowercase)
• -numbers
• -comma
• -underscore
• -period
• Number of characters
• -14 characters some to 225 characters
• To hide a file Use period at the beginning of the
  file name

3
File System

• How to organize all the programs and data on the
  storage device of the computer?
• Hierarchical structure
• -Like a family tree

4
Family Tree
5
Unix Tree
6
Navigation a sample tree
7
Navigation

• Via listing of the directories
• -End to a directory
• eg, /home/ce144f15/Personal
• -End to a file
• eg, /home/ce144f15/UNX122/Labs/Lab1/lab1a
• Via symbols
• / .. ../.. ../../../..

8
Types of Pathnames

• Absolute pathname
• -Begins from root
• eg,
• cd /home/ce144f15/UNX122
• eg,
• cd /UNX122/Labs/Lab1/lab1a
• ( represents /home/username)

9
Types of Pathname

• Relative pathname
• -Begins from the current directory
• eg,
• cd ../Labs/UNX122
• more ../Document/readme

10
Task 1

• Assume your current directory is not known. What
  command changes your current directory to a
  directory named Education, which is listed in a
  directory named Proposals, which is listed in
  your home directory?
• 2. From your home directory, what command do you
  enter to edit a file UNIX-class that is listed in
  the Proposal directory?

11
Task1 (cont.)

• 3. From your home directory, how can you create a
  directory Rejected, listed in the Proposals
  directory?
• 4. How would you copy a file marks from your home
  directory into Education, a subdirectory of the
  Proposals directory.
• 5. How can you copy all files from the current
  directory to the parent?

12
Access Permissions

• Who should have what access to what?
• who
• user (u), group (g), others (o)
• What access
• read, write(modify), execute
• what
• Directories
• Files

13
Identifying the Fields

• drwxrwxrwx 4 John Students 533 Sept 20
  1945 myfile
• Permission links owner group size date of
  modif. name

14
Example

• How do you manage these two files?
• -Plans (to a new product)
• -Memo (to all)

15
Chmod Relative Method

• Chmod who operation permission filename
• Who
• u(user), g(group), o(others)
• Operation
• (add), - (remove), (set permission)
• Permission
• r (read), w (write), e(execute)

16
Relative Method (examples)

• Add permission
• chmod grw filename
• chmod ox filename
• Remove permission
• chmod g-w file.name
• chmod a-w file.name
• (remove w for all, ugo)
• Set permission
• chmod orx filename
• chmoc gorx filename

17
Task 2

• What permissions are granted, to which classes of
  users, for a file with the following permissions
  field
• -r-x- - - - - -
• What command would you use to change a files
  permissions to include read, write, and execute
  permission for the group only.
• What would the files permission field look like
  after you changed its mode as above.

18
Chmod Absolute Method

• Use octal number to represent binary
• 1 (add) 0 (remove)
• Octal Binary
• 0 000
• 1 001
• 2 010
• 3 011
• 4 100
• 5 101
• 6 110
• 7 111

19
Relative Method

• 755 111101101rwxr-xr-x
• R-----------100 ------------4
• W-----------010------------2
• X-----------001-------------1
• Chmod 777 filename
• Chmod 741 filename

20
Task3

• Fill in the blank spaces in the following table

21
Creating a mask

• How the initial setting permissions are
  established?
• Default permissions
• -file 666
• -Directory 777
• The umask command automatically sets the file
  permissions upon creation of the file
• . To automatically establish file permission upon
  creation
• umask mask

22
Mask (cover, deny)

• Mask is represented by number
• 0 mask nothing, allow everything
• mask execute, allow
• mask write, allow
• Mask write and execute, allow
• mask read, allow
• 6 mask read write and allow only x

23
Conceptual Method

• Umask 022
• For a directory results in
• Drwxr-xr-x
• For a file
• -rw-r- -r- -
• Tell me why?

24
Compare

• Directory Default permission
• d rwx rwx rwx (777)
• umask 022
• 0 2 2
• Result
• rwx rwx rwx
• 0 2 2
• rwx r-x r-x

25
Compare

• File Default permission
• -rw-rw-rw
• Umask 022
• Result
• Rw- rw- rw-
• 0 2 2
• Rw- r- - r - -

26
Calculation Method

• Setting Directory permissions
• To set mask for newly-created directories tor w
  x r - - r - -
• Determine octal number 744
• Subtract 777 from 744 033
• Issue command umask 033
• Issue command umask to verify change
• The Same for file. Just Remember the default
  permission for file is different.

27
Task 4

• 1. What command sets the permission fields of all
  newly created directories to read, write, and
  execute for owner, and execute only for everyone
  else?

28
Task 4

• 2. If umask is 022 and the permissions on a file
  named scriptA are rwxr-xr-x, what are the
  permissions for the resulting files when you
  enter the following commands?
• touch abc
• mkdir def
• who gt ghi
• Cp scriptA scriptB