| / | The starting point of any UNIX/LINUX system is the root directory, represented by /. Everything else in the system appears under this. |
| binaries (executable files) |
| /bin | The binaries for use by all users are contained under /bin directory. For example - the files for executable commands like grep, date, cat etc., appear as a file under this directory. |
| /opt/{app}/bin | (alternate /bin directory) The binaries for any external software (which is not part of the OS distribution) are normally stored in application specific directory created under /opt. For example - the binaries for apache web server can be stored under /opt/apache/bin directory. (see /opt later). |
| /home/{user}/bin | (alternate /bin directory) Users can install software under their respective home directories, and the binaries for the same stored in user specific directories. For example - all binaries installed by user biswajit can be found under /home/biswajit/bin directory. |
| /sbin | Contains all system binaries needed for configuring the system, for example - fdisk, fsck etc. |
| /lib | The executable binaries under /bin and /sbin normally reference one or more libraries. These libraries are stored under this directory. |
| /opt | Any software not part of the UNIX/LINUX distribution is normally installed under the optional software directory /opt. This can contain sub-directories like /bin, /lib underneath it. |
| configuration |
| /boot | Contains all files needed to boot the OS. It may also contain boot-loader files. |
| /etc | The *.conf files for configuring the system are stored under /etc directory. |
| /etc/init.d | All scripts for starting/stopping daemons (services) are stored in this directory. |
| /etc/skel | The skeleton (template) directory structure which is copied to the home directory of each newly created user. |
| data |
| /home | The parent home directory containing data folder for each user. |
| /home/{user} | The home directory for the specific user. For example - the home directory for user biswajit may be /home/biswajit. |
| /root | The data folder for root user is normally /root, instead of /home/root folder. |
| /srv | Any data served from the system, like ftp or www, can be contained in this directory. |
| /media | The mount point for all removable medias like CD, USB devices. |
| /media | The mount point for all removable medias like CD, USB devices. |
| /mnt | A temporary mount point used for administration purpose. |
| /tmp | This directory stores temporary data managed by the operating system. The OS may store all such files either in the disk or in RAM as it decided. |
| in-memory data (no physical file) |
| /dev | This directory is used by kernel to organize physical devices like CD, HDD etc. |
| /dev/tty | Contains directory like dev/tty1, /dev/tty2, etc., representing the terminals/consoles connected to the system. |
| /dev/null | A special device folder that ignores any input to it. It is useful in discarding unwanted outputs. |
| /dev/proc | Provides a view of the kernel and the processes it manages at the moment of time. |
| /usr | (Unix System Resources) This directory is used to store shared/read-only data. |
| /var | Any data with unpredictable size is stored in this directory. |
| /var/log | Contains the log files from different applications. |
| /var/cache | Stores cache data for applications. |
| /var/spool | The spool directory for mail, printer etc. |