UNIX File System Organization
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Questions and Answers

What do the permission bits determine?

  • The file's size and creation date
  • The backup frequency for the file
  • What operations can be performed on a file and by whom (correct)
  • The file format and encoding used

    • Which command would you use to inspect the values of the permission bits for a file?

  • chmod
  • ls -l (correct)
  • file
  • touch

    • How many permission bits are associated with the owner of a file?

  • Nine
  • Twelve
  • Three (correct)
  • Six

    • In octal representation, what value corresponds to the read bit for the file owner?

    <p>4</p> Signup and view all the answers

    When a file is executed, what are the two types of executable files that might be encountered?

    <p>Binaries and scripts</p> Signup and view all the answers

    What does the execute bit on a directory allow you to do?

    <p>Search or enter the directory</p> Signup and view all the answers

    Which attribute is controlled by permissions on a file's parent directory?

    <p>The ability to rename the file</p> Signup and view all the answers

    What is represented by the first digit in an octal number for permission bits?

    <p>Owner permissions</p> Signup and view all the answers

    What does the first octal digit in a file specification represent?

    <p>Permissions for the owner</p> Signup and view all the answers

    When using the mnemonic syntax for chmod, what does 'o' stand for?

    <p>Others</p> Signup and view all the answers

    What does the command 'chmod 711 myprog' grant to the owner of the file?

    <p>Read, write, and execute permissions</p> Signup and view all the answers

    Which command is used to change the ownership of a file?

    <p>chown</p> Signup and view all the answers

    If you need to change a file's group ownership, what is a requirement?

    <p>You must be the superuser or the file's owner</p> Signup and view all the answers

    Which octal digit in a four-digit chown command represents the special bits?

    <p>First</p> Signup and view all the answers

    Which flag is used with chown and chgrp to change settings recursively?

    <p>-R</p> Signup and view all the answers

    What permission combination is represented by the octal number '7'?

    <p>Read, write, and execute permissions</p> Signup and view all the answers

    What is one challenge associated with the organization of UNIX file systems?

    <p>Different types of files are scattered randomly around the namespace.</p> Signup and view all the answers

    Which directory is specifically designated for temporary files in the UNIX file system?

    <p>/tmp</p> Signup and view all the answers

    What combination of bits allows the contents of a directory to be listed?

    <p>Read and execute bits</p> Signup and view all the answers

    Which command can be used to determine the type of an existing file?

    <p>file</p> Signup and view all the answers

    Where is the operating system kernel typically located?

    <p>/boot</p> Signup and view all the answers

    What does the setgid bit do when set on a directory?

    <p>Causes newly created files to take the group ownership of the directory</p> Signup and view all the answers

    What does the sticky bit prevent when set on a directory?

    <p>Deleting or renaming files by non-owners</p> Signup and view all the answers

    What is a common characteristic of the /etc directory in UNIX systems?

    <p>It holds critical system and configuration files.</p> Signup and view all the answers

    Which of the following is NOT a standard file type defined by most filesystem implementations?

    <p>Bitwise files</p> Signup and view all the answers

    Which octal value corresponds to the setuid bit?

    <p>4000</p> Signup and view all the answers

    Why is it recommended to leave the file tree organization unchanged in UNIX systems?

    <p>It can create problems due to hidden dependencies.</p> Signup and view all the answers

    Which command provides a detailed listing of files and directories?

    <p>ls -l</p> Signup and view all the answers

    To enable programs to access files that would otherwise be off-limits, which bits need to be set on the executable file?

    <p>Setuid and setgid bits</p> Signup and view all the answers

    Which option describes the purpose of the 'ls -ld' command?

    <p>It shows detailed information of a directory without listing its contents.</p> Signup and view all the answers

    Which attributes are mostly of concern to a system administrator according to the content?

    <p>Link count, owner, group, and mode</p> Signup and view all the answers

    Which of the following statements about the setgid bit is true?

    <p>It allows programs to run with the group's permissions</p> Signup and view all the answers

    What does the umask command do in a Unix-like system?

    <p>Influences default permissions for newly created files.</p> Signup and view all the answers

    What is the purpose of the a flag in Linux file attributes?

    <p>It makes a file append-only.</p> Signup and view all the answers

    What characterizes an Access Control List (ACL)?

    <p>It lists individual permission rules for each user or group.</p> Signup and view all the answers

    Which of the following is NOT a way that ACLs can be implemented in a Linux system?

    <p>Via kernel modules for specific applications.</p> Signup and view all the answers

    Which command is used to view file attributes including Linux bonus flags?

    <p>lsattr</p> Signup and view all the answers

    What type of permissions can advanced ACL systems allow administrators to specify?

    <p>Partial sets of permissions.</p> Signup and view all the answers

    Which command is NOT typically used to manipulate POSIX ACLs?

    <p>chown</p> Signup and view all the answers

    How is the umask specified?

    <p>As a three-digit octal value.</p> Signup and view all the answers

    Study Notes

    File Tree Organization

    • UNIX systems have never been well-organized.
    • Various incompatible naming conventions.
    • Different types of files can be scattered randomly.
    • Files are often divided by function instead of the frequency of changes.
    • /etc directory contains files that are never customized and files that are entirely local.
    • It is not recommended to change the default organisation due to hidden dependencies.
    • Root filesystem contains the root directory, minimal set of files and subdirectories.
    • OS kernel lives under /boot.
    • /etc directory holds critical system and configuration files
    • /sbin and /bin are for important utilities
    • /tmp is often used for temporary files.
    • /dev has traditionally be part of the root filesystem, but now it is a virtual filesystem mounted separately.

    Standard Directories

    • /bin contains essential binaries, accessible to all users.
    • /boot contains files required for booting the system, including the kernel.
    • /dev contains device files allowing interaction with hardware.
    • /etc contains system-wide configuration files.
    • /home contains user home directories.
    • /lib contains libraries needed by many programs.
    • /lost+found holds files recovered from a damaged filesystem.
    • /mnt contains mount points for other filesystems.
    • /media contains mount points for removable media (like USB drives).
    • /opt contains optional software packages.
    • /proc contains virtual filesystem representing running processes.
    • /root is the home directory of the root user.
    • /run contains runtime data, like system state and socket files.
    • /sbin contains essential system binaries.
    • /srv contains data for services (e.g., websites).
    • /sys contains virtual filesystem representing hardware information.
    • /tmp stores temporary files that are automatically deleted on reboot.
    • /usr contains user programs and utility files.
    • /var stores variable (changing) data, such as logs and mail.

    File Types

    • Seven types of files are defined:
      • Regular files
      • Directories
      • Character device files
      • Block device files
      • Local domain sockets
      • Named pipes (FIFOs)
      • Symbolic links
    • The "file" command can be used to determine the type of an existing file.
    • Knowing the standard file types is important for understanding how systems operate.

    File Attributes

    • Nine permission bits determine which operations can be performed on a file by whom.
    • Permission bits are grouped into three sets: owner, group, and other (everyone else).
    • Each set has three bits: read, write, and execute.
    • File permissions are represented using octal numbers (base 8) because each octal digit represents three bits.
    • The top three bits (400, 200, 100) control access for the owner.
    • The middle three bits (40, 20, 10) control access for the group.
    • The bottom three bits (4, 2, 1) control access for everyone else.

    File Attributes (cont.)

    • For regular files:
      • The read bit allows the file to be opened and read.
      • The write bit allows the file's contents to be modified or truncated.
      • The execute bit allows the file to be executed.
    • For directories:
      • the execute bit (often called the "search" bit) allows the directory to be entered.
      • The read bit allows listing the contents of the directory.
      • The write bit allows files to be created, deleted, and renamed within the directory.

    Permissions

    • The setuid (Set user ID) and setgid (Set group ID) bits can be set on executable files.
      • When set, they allow programs to access files and processes that would otherwise be off-limits to the user running them.
    • If the setgid bit is set on a directory, newly created files inherit the group ownership of the directory.
    • The sticky bit (octal value 1000) on a directory prevents deleting or renaming files unless you are the owner of the directory, the owner of the file, or the superuser.

    Inspecting File Attributes

    • The ls -l (or ls -ld for directory) command displays details for a file.
    • Attributes displayed include link count, owner, group, mode, size, last access time, last modification time, and file type.
    • chmod command is used to change the mode (permissions) of a file.
    • chown command changes a file’s ownership.
    • chgrp command changes its group ownership.
    • umask modifies the default permissions for newly created files.
    • The lsattr and chattr commands view and change Linux's supplemental file flags (e.g., append-only or immutable).

    Access Control Lists (ACLs)

    • Access Control Lists are a more powerful but more complex way to regulate access compared to standard file permissions.
    • An ACL is associated with each file or directory, and lists the permission rules.
    • Each rule in an ACL is called an access control entry (ACE).
    • An ACE identifies the user or group it applies to and specifies a set of permissions.
    • ACL implementation can be done by the kernel, individual filesystems, or by higher-level software like NFS and SMB servers.
    • Linux uses POSIX ACLs.
    • Commands getfacl and setfacl are used to manipulate ACLs.

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    Related Documents

    Chapter5(1) (2).ppt

    Description

    Test your knowledge about the organization of UNIX file systems, including the purpose of standard directories such as /bin, /etc, /boot, and /dev. Understand the rationale behind directory structure and file management in UNIX systems.

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