Operating System-Unix [3i Infotech Placement]: Sample Questions 34 - 35 of 78

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Question 34

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Describe in Detail

Essay▾

How do you change file access permissions?

Explanation

  • chmod command changes file permissions with the.
  • In Unix, file permissions establish the different types of access to a file by both access and classe types.
  • The access classes are “user” , “group” , “other” and “all” - User who owns the file, a specific group of users, the other remaining users who are not in the group.
  • Read, write and execute are the access types- determine what may be done with file by each access class.

There are two ways of using chmod to change file permissions:

  • Symbolic method:
    • This is the first and probably easiest way.
    • Is relative method- specifies access class and types with single letter abbreviations.
  • Absolute form:
    • Specifies a set of three numbers that determine all the access classes and types.

Question 35

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Describe in Detail

Essay▾

What are various IDs associated with a process?

Explanation

  • Every process in unix is identified with a unique integer called processed.
  • Each process also associated with a particular user called the ‘owner’ - whose privileges transfer to the process.
  • ‘UserId’ is the identification of the user.
  • Owner is the user who executes the process.
  • ‘Effective UserID’ determines the access privileges for accessing resources like files.
  • getpid ()
    • process id
  • getppid ()
    • parent process id
  • getuid ()
    • user id
  • geteuid ()
    • effective user id

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