File system hirerachy of Linux

                                           File System Structure Of  Linux
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/root   /home   /boot   /sbin   /bin    /usr   /var   /dev   /etc    /proc    /tmp    /opt    /media    /lib
                    “/”  this directory is called as root directory
                      It is the top of filesystem structure
 All other directories are mounted under it.
(1) /root : this is default homedirectory of administrator
             > Every single file and directory starts from the root directory.
             > Only root user has write privilege under this directory.
             > Please note that /root is root user’s home directory, which is not same as /.
(2) /home : It contains all users home directories
             > Home directories for all users to store their personal files.
             > For example: /home/john, /home/nikita
(3) /boot : It contains bootable files like kernel  (initrd image),  bootloader (GRUB),installer                                      (ANACONDA-ks.cfg)
             > Contains boot loader related files.
             > Kernel initrd, vmlinux, grub files are located under /boot
             > For example: initrd.img-2.6.32-24-generic, vmlinuz-2.6.32-24-generic
(4) /sbin : It contains administrative commands used by super user (root)
                                       i.e. ADMINISTRATOR
             > Just like /bin, /sbin also contains binary executables.
             > But, the linux commands located under this directory are used typically by
              system aministrator, for system maintenance purpose.
             > For example: iptables, reboot, fdisk, ifconfig, swapon
(5) /bin  : It contains commands used by superuser & normal user
             > Contains binary executables.
             > Common linux commands you need to use in single-user modes are located
              under this directory.
             > Commands used by all the users of the system are located here.
             > For example: ps, ls, ping, grep, cp.
(6) /usr  : It contains the packages and application which are available for user
                       (similar to program files on windows)
             > Contains binaries, libraries, documentation, and source-code for
              second level programs.
             > /usr/bin contains binary files for user programs. If you can’t find a user binary
              under /bin, look under /usr/bin. For example: at, awk, cc, less, scp
             > /usr/sbin contains binary files for system administrators. If you can’t find a
              system binary under /sbin, look under /usr/sbin.
             > For example: atd, cron, sshd, useradd, userdel /usr/lib contains libraries
              for /usr/bin and /usr/sbin
             > /usr/local contains users programs that you install from source.
             > For example, when you install apache from source, it goes
               under /usr/local/apache2
(7) /var  : It contains variable information such as logs and print queries
             > var stands for variable files.
             > Content of the files that are expected to grow can be found under this directory.
             > This includes — system log files (/var/log); packages and database files                           (/var/lib); emails (/var/mail); print queues (/var/spool); lock files                            (/var/lock); temp files needed across reboots (/var/tmp);
(8) /dev  : This directory contains devices modes through which the o/s can access
                               hardware (on software device on the system)
             > Contains device files.
             > These include terminal devices, usb, or any device attached to the system.
             > For example: /dev/tty1, /dev/usbmon0
(9) /etc  : It contains all configuration files
             > Contains configuration files required by all programs.
             > This also contains startup and shutdown shell scripts used to
              start/stop individual programs.
             > For example: /etc/resolv.conf, /etc/logrotate.conf
(10) /proc : This directory contains current running process information.
             > Contains information about system process.
             > This is a pseudo filesystem contains information about running process.
             > For example: /proc/{pid} directory contains information about the process
              with that particular pid.
             > This is a virtual filesystem with text information about system resources.
             > For example: /proc/uptime
(11) /tmp  : This directory contains temporary files used by the system
             > Directory that contains temporary files created by system and users.
             > Files under this directory are deleted when system is rebooted.
(12) /opt  : It contains the third party application
             > opt stands for optional.
             > Contains add-on applications from individual vendors.
             > add-on applications should be installed under either /opt/ or /opt/ sub-directory.
             > Eg    : Core word effect, Sun star office
(13) /media: Removable media is stored under this directory.
             > Temporary mount directory for removable devices.
             > For examples, /media/cdrom for CD-ROM; /media/floppy for floppy drives;                          /media/cdrecorder for CD writer
(14) /lib  : It contains libraries need by no. of different application as well as linux kernel
             > Contains library files that supports the binaries located under /bin and /sbin
             > Library filenames are either ld* or lib*.so.*
             > For example:,
       DEVICE                                       IDE                                 SATA
   primary master                          /dev/hda                                 /dev/sda
   primary slave                            /dev/hdb                               /dev/sdb
  secondary master                     /dev/hdc                                 /dev/sdc
  secondary slave                      /dev/hdd                                  /dev/sdd

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