B.2. Organization of the Filesystem Hierarchy

B.2.1. The Root Directory

A Debian system is organized along the File Hierarchy Standard (FHS). This standard defines the purpose of each directory. For instance, the top-level directories are described as follows:

/bin/: basic programs;
/boot/: Linux kernel and other files required for its early boot process;
/dev/: device files;
/etc/: configuration files;
/home/: user's personal files;
/lib/: basic libraries;
/media/*: mount points for removable devices (CD-ROM, USB keys and so on);
/mnt/: temporary mount point;
/opt/: extra applications provided by third parties;
/root/: administrator's (root's) personal files;
/sbin/: system programs;
/srv/: data used by servers hosted on this system;
/tmp/: temporary files; this directory is often emptied at boot;
/usr/: applications; this directory is further subdivided into bin, sbin, lib (according to the same logic as in the root directory). Furthermore, /usr/share/ contains architecture-independent data. /usr/local/ is meant to be used by the administrator for installing applications manually without overwriting files handled by the packaging system (dpkg).
/var/: variable data handled by daemons. This includes log files, queues, spools, caches and so on.
/proc/ and /sys/ are specific to the Linux kernel (and not part of the FHS). They are used by the kernel for exporting data to user-space.

B.2.2. The User's Home Directory

The contents of a user's home directory is not standardized, but there are still a few noteworthy conventions. One is that a user's home directory is often referred to by a tilde (“~”). That is useful to know because command interpreters automatically replace a tilde with the correct directory (usually /home/user/).

Application configuration files are often stored directly under the user's home directory, but their names usually start with a dot (for instance, the mutt email client stores its configuration in ~/.muttrc). Filenames that start with a dot are hidden by default, and ls only lists them when the -a option is used.

Some programs use multiple configuration files organized in one directory (for instance, ~/.evolution/). Some applications (such as the Iceweasel web browser) also use their directory to store a cache of downloaded data. This means that those directories can end up using a lot of disk space.

Graphical desktops usually display the contents of the ~/Desktop/ directory (or ~/Bureau/ or whatever the appropriate translation is for systems not configured in English) on the desktop (ie, what's visible on screen once all applications are closed or iconized).

Finally, the email system sometimes stores incoming emails into a ~/Mail/ directory.