File Systems and Permissions

A ___ (or symlink) is a special type of file that points to another file or directory. Instead of containing its own data, it stores a path to a target location. It acts like a shortcut in Linux. If a program accesses the ___, Linux automatically redirects it to the target file or directory.

symbolic link

ls -l

In ___ output, the first character indicates the file type.

ln -s target link_name

Creates a symbolic link named link_name pointing to target.

Metadata

Information stored about a file rather than the file’s actual contents. In Linux, ___ describes properties of a file such as ownership, permissions, timestamps, size, and inode information. Helps the operating system manage files and allows users to view details about them.

Inode

Internal filesystem data structure storing metadata about a file except its filename.

hard link

A ___ is another directory entry that points to the same inode as an existing file. Because both names reference the same inode, they both refer to the exact same file data on disk. Unlike a symbolic link, a ___ does not point to a pathname. Instead, it directly references the same inode and underlying file contents.

chmod

Stands for change mode. It is a Linux command used to change file or directory permissions.

User classes

___ are categories of users used by Linux permissions to determine who can read, write, or execute files and directories. These user classes are commonly used with the chmod command to modify permissions.

chmod operators

Are symbols used with the chmod command to control how permissions are changed on files and directories.

permissions

Determine what actions users can perform on files and directories (Ex: r = read, w = write, x = execute).

permission numeric values

___ are the numeric representations of Linux file permissions used with commands like chmod. (Ex: r = 4, w = 2, x = 1)

Read Permission

Permission allowing viewing file contents. Has numeric value of 4

write permission

Permission allowing modification of a file. Has numeric value of 2

execute permission

Permission allowing a file to run as a program or script. Has numeric value of 1.

directory execute permission

Allows entering or traversing a directory.

umask

Stands for user file-creation mode mask. It controls the default permissions assigned to new files and directories when they are created in Linux. Removes permissions from the system’s default permission settings.

666

Default starting ‘Files’ permissions are usually

777

Default starting ‘Directories’ permissions are usually

.

The ___ directory entry refers to the current directory in Linux. It is a special directory entry automatically present inside every directory and is commonly used to reference the directory you are currently working in.

..

The ___ directory entry refers to the parent directory in Linux. It is a special directory entry automatically present inside every directory and is used to move up one level in the filesystem hierarchy.

directory link count

___ is the number of hard links that point to a directory’s inode. This value appears in the ls -l output immediately after the permissions field.

empty directory link count

An ___ starts at 2 in Linux because two hard links already point to the directory’s inode.

manual hard links

___ to directories are generally forbidden in Linux filesystems because they can create filesystem loops and cyclic directory structures. A hard link points directly to an inode. Allowing users to manually create hard links to directories would make the filesystem graph circular instead of hierarchical.

timestamp

Metadata recording times such as modification or access time.

filesystem

Structure Linux uses to organize and store files/directories.

Owner

[User Class] u

Group

[User Class] g

Others

[User Class] o

all users

[User Class] a

+ =

[chmod Operators] Add Permissions

- =

[chmod Operators] remove permissions

= = set

[chmod Operators] exact permissions

read

[Permissions] r

write

[Permissions] w

execute

[Permissions] x

4

[Permissions Numeric Values] r

2

[Permissions Numeric Values] w

1

[Permissions Numeric Values] x