Linux filesystem structures.

1. / – Root

• 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. /bin – User Binaries

• 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.

3. /sbin – System Binaries

• 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

4. /etc – 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

5. /dev – Device Files

• Contains device files.


• These include terminal devices, usb, or any device attached to the
  system.


• For example: /dev/tty1, /dev/usbmon0

6. /proc – 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

7. /var – Variable Files

• 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. /tmp – Temporary Files

• Directory that contains temporary files created by system and users.


• Files under this directory are deleted when system is rebooted.

9. /usr – User Programs

• 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

10. /home – Home Directories

• Home directories for all users to store their personal files.


• For example: /home/john, /home/nikita

11. /boot – Boot Loader Files

• 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

12. /lib – System Libraries

• Contains library files that supports the binaries located under /bin and
  /sbin


• Library filenames are either ld* or lib*.so.*


• For example: ld-2.11.1.so, libncurses.so.5.7

13. /opt – Optional add-on Applications

• opt stands for optional.


• Contains add-on applications from individual vendors.


• add-on applications should be installed under either /opt/ or /opt/
  sub-directory.

14. /mnt – Mount Directory

• Temporary mount directory where sysadmins can mount filesystems.

15. /media – Removable Media Devices

• Temporary mount directory for removable devices.


• For examples, /media/cdrom for CD-ROM; /media/floppy for floppy drives;
  /media/cdrecorder for CD writer

16. /srv – Service Data

• srv stands for service.


• Contains server specific services related data.


• For example, /srv/cvs contains CVS related data.

ref:　　Linux
Directory Structure (File System Structure) Explained with
Examples

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