Linux File System Hierarchy

/boot: It has files which are required for booting Linux OS, and contains kernel supportive information. 

                Grub: It is a boot loader from Linux environment


                System.map: It is a symbol table which is a look-up between symbol names and their 
                addresses in memory


                initrd: It is an initial root file system that is mounted prior to when the real root file system is 
                available


                Kernel / vmlinuz: It is the compressed version kernel image. Vmlinuz is the name of the Linux 
                kernel executable

/bin : Consists of the executable files can be accessed by local and root user. 

/dev : stores all the hardware device related information 

                /dev/cdrom: Represent CD-ROM drive


                /dev/console: Similar to tty0. 


                /dev/fd : Represent Floppy drive


                /dev/full : Produces continuous stream of NULL (zero value) bytes, and returns a “disk full” 
                message when written to.


                /dev/had : The master device on primary IDE channel.


                /dev/initctl: Someone wanting to interact  with  init  should use the /dev/initctl control channel


                /dev/kmsg: This character device node provides userspace access to the kernel’s printk buffer.


                /dev/log: The /dev/log socket is created by the system logger.


                /dev/loop: It is loop device file.


                /dev/lp0: The first parallel port.


                /dev/mapper: Device-mapper serves as a generic framework to map one block device onto 
                another. 


                /dev/md0: Multiple Device driver aka Linux Software Raid


                /dev/mem: It provides access to system physical memory, not virtual.


                /dev/midi: It is a technical standard that describes a protocol, digital interface and connectors 
                and allows a wide variety of electronic musical instruments, computers and other related 
                devices to connect and communicate with one another.


                /dev/mixer: It is the legacy OSS device and is no longer included n the kernel. 


                /dev/null: Accepts and discards all input; produces no output.


                /dev/nvram: It provides access to the machine device driver for accessing or modifying 
                machine specific nonvolatile RAM.


                /dev/par0: Manages parallel devices


                /dev/parport0: Parallel port number 0.


                /dev/ppp: It is designed around providing an IP network connection over a serial link.


                /dev/ptmx: It is the “pseudo-terminal master multiplexer”.


                /dev/pts: pseudo terminal slave.. without it, you wouldn’t have a command line with terminals. 
                When a process opens 

                /dev/ramdisk: RAM disks use the normal RAM in main memory as if it were a partition on a 
                hard drive rather than actually accessing the data bus normally used for secondary storage                         such as hard disk.


                /dev/rtc: real-time clock device


                /dev/sda: SCSI device A


                /dev/sg0: It is a generics SCSI device, used to access writing capabilities of CD drive


                /dev/shm /dev/shm: It is nothing but implementation of traditional shared memory concept. 


                /dev/snd: It is a modern ALSA based system where the sound card is controlled by the 
                devices in /dev/snd


                /dev/tty0: It is the first virtual console.


                /dev/tty1: It is the second virtual console.


                /dev/usb: It contains most of USB device nodes.


                /dev/vcs: It is a character device which refers to memory of currently displayed virtual console 
                terminal.


                /dev/zero: It accepts and discards all input; produces continuous stream of NULL (zero value) 
                bytes.

/etc : Its home for the all the configuration files. 

/home : Home directory for the local users. 

/lib : Stores all library files 

/opt : Third party application, and for storage purpose 

/proc : Stores all process related files 

/mnt /media /music :for the mounting the file system and to store the media files. 

/sbin : Consists of the executable files can be accessed by root user only. 

/selinux : Consists of files which provides more security to the system. 

/sys : Stores hardware related files 

/tmp : Stores temporary files 

/usr : It consists of user programs. 

/var : All the variable data like spooling data like log messages are stored here.