Files Permissions

File Permission

Bit Position	1	2	3	4	5	6	7	8	9
Permission	r	w	x	r	w	x	r	w	x
Binary Value	4	2	1	4	2	1	4	2	1

Common Numeric Combos: • 7 (4+2+1): Full Access (r w x) • 6 (4+2): Read/Write (r w —) • 5 (4+1): Read/Execute (r — x) • 4: Read Only (r — —) • 0: No Access (— — —)

Command	Syntax Type	Example Command	Logical Result / Use Case
chmod	Numeric	chmod 755 file	Owner: Full, Group/Other: Read/Run. Standard for scripts.
	Symbolic (+/-)	chmod g+w file	Add write permission to the group only. Leaves others alone.
	Symbolic (=)	chmod o=rx file	Explicitly set Others to Read/Run. Wipes out any previous w bit.
	Recursive	chmod -R 700 dir/	Advanced: Locks a folder and everything inside to the Owner only. -R means recursive
	Verbose	chmod -v 644 file	Advanced: Prints a message explaining the change (e.g., mode of 'file' changed to 0644).
	Reference	chmod --reference=A B	Advanced: Makes File B have the exact same 9 bits as File A.
chown	Basic	chown pavan2 file	Changes the primary owner to pavan2.
	Combined	chown pavan:devops file	Advanced: Changes both Owner and Group in one command.
	Group Only	chown :prod file	Advanced: Changes only the group (shorthand for chgrp).
	Conditional	chown --from=root pavan file	Advanced: Only swaps owner if the current owner is root.
	Recursive	chown -R pavan:devops dir/	Advanced: Fixes ownership for a whole project directory tree.
chgrp	Basic	chgrp devops file	Changes the group to devops. No sudo needed if you are in that group.
	Recursive	chgrp -R prod dir/	Advanced: Mass-updates group for entire directory structures.
	Changes Only	chgrp -c devops *	Advanced: Only reports if a file actually changed its group (ignores correct ones).
	Silent	chgrp -f prod file	Advanced: Suppresses “Permission Denied” errors if you hit a file you don’t own.

Pattern (rwx)	Identity of User	Action Attempted	Result	Deep Logic
rwx------	Owner	Read/Write/Run	Allowed	You are the owner; you have full bits.
rwx------	Group member	Read/Write/Run	Denied	You aren’t the owner; the group bits are all ---.
---rwx---	Owner	Read	Denied	The Owner Trap: You are the owner, but your specific bits are ---. Linux stops here and ignores the group’s rwx.
---rwx---	Group member	Read/Write/Run	Allowed	You aren’t the owner, but you match the Group which has rwx.
rw-r-----	Group member	Write	Denied	You match the group, but they only have r-- (Read). Write is missing.
-------r-	Everyone	Read	Allowed	No one owns it or groups it with rights, but the “Others” bit allows everyone to read.
r-xr-xr-x	Any User	Run Script	Allowed	Everyone has the x (Execute) bit.

Scenario Pattern	Your Identity	Logic Result	Why?
---rwx---	Owner	DENIED	You matched “Owner” first. Your bits are ---. You are blocked.
---rwx---	Group Member	GRANTED	You are not the owner. You matched “Group.” Group bits are rwx.
rw-r--r--	Owner	READ/WRITE	You matched “Owner.” You can Read and Write.
rw-r--r--	Group Member	READ ONLY	You matched “Group.” Group bits only allow r--.
---------	Root User	GRANTED	The Exception: Root (UID 0) bypasses this algorithm entirely.

https://www.youtube.com/watch?v=eWsCbBfxZ04&list=PLbvUFWvKlQnmiDGAW7T_gZNgJN2bmQsFu&index=10