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Linux File System Hierarchy

Directories and the files are organized into a single rooted reverse tree structure. File system begins at the / directory. Names are case sensitive and all the path are delimited by ‘/’.

• Home directories : /root, /home/username
  User Executable : /usr/bin, /usr/local/bin, /bin
  System Executable : /usr/sbin, /usr/local/sbin, /sbin
  Kernels and bootloader : /boot
  Configuration : /etc
  System information : /proc, /sys
  Server data : /var, /srv
  Libraries : /lib, /usr/lib, /usr/local/lib
  Mount points : /media, /mnt
  Temporary File : /tmp

.
??? bin
??? boot
??? dev
??? etc
??? home
??? lib
??? media
??? mnt
??? proc
??? root
??? sbin
??? srv
??? sys
??? tmp
??? usr
??? var


List the first level directories of the system.
tree -d -L 1

Linux naming convention

• All characters are allowed except the forward slash
  Size of the name can be up to 255 characters
  Name are case sensitive

However, it is unwise to use certain characters in file name and directory names

Eg:
Access a file having special character in file name such as spaces

ls -l “Hello World”

OR

ls -l Hello\ World

File and Directory permissions
Users

• Every user has an ID (unique number). User root has the ID 0. Normally UID start at 500s
  These details are stored in /etc/passwd
  Each user can get a home directory at /home
  User need permission to read files which owned by other user

Groups

• Users are grouped into a user group
  Each group has unique ID; GID
  These information are stored in /etc/group
  All users in the same group can share the files each other

Linux access permission

This is totally based on the ownership where it has 3 levels

__ User (u)
|
Ownership _______ Group (g)
|
|__ Other (o)

This is also known as Discretionary Access Control (DAC). Users can perform 3 action on files and the directories

__ read (r)
|
File ________ write (w)
|
|__ execute (x)


__ list the content (r)
|
Directory ________ modify file and sub-dir (w)
|
|__ open, access move (x)

u g s | r w x | r w x | r w x

There is nobody I know better than you to teach us on Linux based OSs. Thanks for sharing.
Also it seems there will be more valuable articles to come in this category

Yes. I like Linux. I couldn't Reply first time. Now I did

Thanks Uditha Sir