Filesystem Hierarchy

[sexyb3rry]

Since Linux is UNIX-like kernel, its hierarchy is very similar which is a very good thing.
(MacOS, I believe is actually UNIX, not a clone like Linux is. So it shares the same hierarchy)

If you have a Linux OS or a Mac OS, and you go to the very 'top' of your directory you will end up in "/".
(These apply to all Unix-like and Unix-clones systems.)

'/' stands for 'root'. This is at the very top of your filesystem structure. everything else in your system will be contained starting here.

The most common directories are:

it all begins with '/' (root)

/bin
/boot
/dev
/etc
/home
/lib (32bit libraries)
/lost+found
/media
/mnt
/opt
/proc
/root
/sbin
/srv
/tmp
/usr
/var

* Some Linux distributions will contain extra Directories like FedoraLinux has "/selinux" and 64bit systems have "/lib64" for the the 64bit libraries, since no OS is 'true' 64 bit yet 32bit and 64 bit libraries are shared.

* Notice how each of those folders have a '/' before them because the '/' is at the top. Nothing is above root (/)

Each directory has its own purpose, but since this is a very, very long topic I will post in a daily basis rather than in one post.

[sexyb3rry]

Everyone of these directories has a a "file permission" which lists who has access to do what with the file or directory.
The result will look something like this:

dr-xr-xr-x.   2 root root  4096 2009-12-22 09:15 bin
dr-xr-xr-x.   5 root root  1024 2009-12-21 21:33 boot
drwxr-xr-x.  19 root root  4320 2009-12-30 00:20 dev
drwxr-xr-x. 113 root root 12288 2009-12-30 00:21 etc
drwxr-xr-x.   4 root root  4096 2009-12-08 23:24 home
dr-xr-xr-x.  10 root root  4096 2009-12-09 01:13 lib
dr-xr-xr-x.   9 root root 12288 2009-12-22 09:15 lib64
drwx------.   2 root root 16384 2009-12-08 23:09 lost+found
drwxr-xr-x.   2 root root  4096 2009-12-21 23:19 media
drwxr-xr-x.   7 root root  4096 2009-12-09 12:40 mnt
drwxr-xr-x.   2 root root  4096 2009-08-25 13:06 opt
dr-xr-xr-x. 176 root root     0 2009-12-30 00:20 proc
dr-xr-x---.   6 root root  4096 2009-12-29 14:24 root
dr-xr-xr-x.   2 root root 12288 2009-12-22 09:15 sbin
drwxr-xr-x.   7 root root     0 2009-12-30 00:20 selinux
drwxr-xr-x.   2 root root  4096 2009-08-25 13:06 srv
drwxr-xr-x.  13 root root     0 2009-12-30 00:20 sys
drwxrwxrwt.  64 root root  4096 2009-12-30 00:33 tmp
drwxr-xr-x.  14 root root  4096 2009-12-08 23:15 usr
drwxr-xr-x.  21 root root  4096 2009-12-08 23:22 var

The command to get this output is:

ls -l /

(this command is pretty much universal on Unix and Unix-like systems. Alexora, open a terminal and type or copy/paste and you will see around the same thing)
The command means
ls = list
-l = long format (this lists the full info about the directory or file)
/ = The root directory which we wanted listed. You can replace this with a different directory or file.

Output might look confusing but it's actually pretty easy. Here is one line of it:

drwxr-xr-x.   4 root root  4096 2009-12-08 23:24 home

The first 10 characters tell you what if it's a file or directory and lists permissions for all users.

the 'd' tells you it's a directory. If there was a '-' instead of a 'd' it would mean it's a file.
r = read
w = write
x = execute
- = Replaces "r", "w" or "x" if according access type is denied

The first character is file type. The next three are the permissions for the "owner" of the file. Second three are permissions for the "group" and last three are the permissions for others.

Owner Group Others

drwxr-xr-x

So in this case the Owner can read/write/execute the Group can read/execute and Others can read/execute

drwxr-xr-x.   4 root root  4096 2009-12-08 23:24 home

I this example the next columns are:
4 = Number of directories
Root = is the owner and/or creator of the file/directory
Root = Group of users the file/directory it belongs to
4096 = Size of file/directory in Megabytes ( I assume...)
2009-12-08 23:24 = Date created or modified
home = name of file/directory all the info belongs to.

(I'm not sure what the "." means... maybe timmy or videodrone can help. When a file or directory in Linux has a "." in the beginning, it means it is a hidden file/directory. But not sure why the period is there )

This is it for now More tomorrow...

[sexyb3rry]

Originally Posted by timmyw3ar

Good post. I hope you continue.

Hmm.. I'm not sure about the "." either. Maybe you were in the parent directory so it showed them?

Hmm... maybe. Thanks for the tip, I will look into it and continue posting a bit later.

[worthiness]

Bit of thread necromancy, but...

You also have at least one non-standard distro, GoboLinux. http://gobolinux.org/ - does not use the standard hierarchy.

[monogroover]

Originally Posted by worthiness

Bit of thread necromancy, but...

You also have at least one non-standard distro, GoboLinux. http://gobolinux.org/ - does not use the standard hierarchy.

Well, GoboLinux does use exactly the same hierarchical paradigm, but it places files where you wouldn't expect them from a traditional point of view.

[monogroover]

Originally Posted by sexyb3rry

drwxr-xr-x.   4 root root  4096 2009-12-08 23:24 home

I this example the next columns are:
4 = Number of directories
Root = is the owner and/or creator of the file/directory
Root = Group of users the file/directory it belongs to
4096 = Size of file/directory in Megabytes ( I assume...)
2009-12-08 23:24 = Date created or modified
home = name of file/directory all the info belongs to.

In your example above:

The '4096' is actually the size of the directory file, in kilobytes. If you want to find out how much data is held in the directory (including the directory file), then you can do (eg)

du -sm /home

.. which will tell you the size it takes up, in megabytes.

The '4' is actually the number of hard links to the directory. Every directory will have at least two hard links (one for the usual name, and one for .). Every time a directory is created underneath it, then a new hard links for .. will be created.

(I'm not sure what the "." means... maybe timmy or videodrone can help. When a file or directory in Linux has a "." in the beginning, it means it is a hidden file/directory. But not sure why the period is there )

If you mean the dot at the end of the permissions, eg at the end of drwxr-xr-x. - then it's to show that the directory has extended attributes (most Linux filesystems support these).

Cheers

[monogroover]

No, sticky bits aren't extended attributes, they are standard. EA's can be used for example to establish access control lists but there are potentially lots of uses.

[cp2141]

Very nice little intro to the Linux/UNIX filesystem. Just a little side note, if anyone wants a quick up-to-speed with Linux/UNIX commands and navigating around, see:
http://freeengineer.org/learnUNIXin10minutes.html

Then you might be able to move around the system a lot better and understand what's actually held in the directories sexyb3rry describes.

[powerofporn]

Here is Filesystem Hierarchy Standard.

[renrouie]

Thanks for the info.