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
