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Linux Filesystem Basics

Terms:

“Directory” A special kind of file that contains links to other files.

“File” is a self-contained piece of information available to the
operating system and any number of individual programs. Files
are owned by the user who creates them.

“Filesystem” Can refer to the filsystem hierarchy (the way files are
organized and managed) or it can refer to the type of
format that is used to store files on a block device
such as Ext4, XFS Fat32 and NTFS.

“Folder” Another name for a directory, especially when working in
graphic environments. Interchangeable with the term
“Directory”

“Link” Refers to a file that points to another file or directory
(symbolic link) or it can refer to a file that has more than
one name. (hard link)

“Mount” Refers to the way devices are made to appear in a Unix/Linux
filesystem. Partitions on hard drives, USB sticks and CD/DVD
are “mounted” to a directory somewhere in the filesystem. This
can be done automatically or manually by a user with root
privileges.

“Path” A path points to a file system location by following the
directory tree hierarchy. Example:

/home/joe/Documents/letter_to_cindy.txt

“Permissions” File attributes that define who can access or change a file
and whether a file can be executed as a program.

“-rwxr-xr-x” Shows file type and permissions.

+————-+——+——-+
| d——— | File Type |
+————-+——+——-+
| – = regular file |
| d = directory |
| l = link |
+————-+——+——-+
| Permission | Octal| Field |
+————-+——+——-+
| -rwx—— | 700 | User |
| —-rwx— | 070 | Group |
| ——-rwx | 007 | Other |
+————-+——+——-+

Octal values:

Read = 4
Write = 2
Execute = 1

8 bits = 1 byte. Uses digits 0 1 2 3 4 5 6 7.

You can set permissions in the file manager or with the commend
“chmod.” Examples:

Set a file to be executable and readable by
by everyone but only writable by you:

‘chmod 755 filemane’

Set execute bit without changing other permisions:

‘chmod +x filename’

When applying permissions to directories on Linux, the
permission bits have different meanings than on regular files.
The write bit allows the affected user to create, rename, or
delete files within the directory, and modify the directory’s
attributes. The read bit allows the affected user to list the
files within the directory. The execute bit allows the affected
user to enter the directory and access files and directories
inside.

“Root” Can refer to the base of a filesystem (“/”) or a user with
administrator privileges for a Unix/Linux computer.

“Tree” A way to visualize filesystem structure.

Dir
├── Dir
│ ├── File
│ ├── File
│ └── Dir
│ └── File
├── File
└── File