What permission is needed to access files inside?

To access files inside a directory, you primarily need the execute (x) permission on that directory.

Let me elaborate:

Execute (x) permission on the directory: This allows you to "traverse" or "pass through" the directory. Without x permission on a directory, you cannot cd into it, or access any files or subdirectories within it, even if you know their full path and have perfect permissions on the files themselves. Think of it as having the key to the door that lets you into the room where the files are stored.

Once you have x permission on the directory to get to the files, you then need the appropriate permissions on the individual file itself to actually read, write, or execute it:

Read (r) permission on the file: To view or copy the contents of the file.
Write (w) permission on the file: To modify or delete the file's contents.
Execute (x) permission on the file: To run the file as a program or script.

Example Scenario:

Let's say you have a directory /home/labex/mydata/ and inside it, a file report.txt.

To simply read report.txt:
- You need x permission on /home
- You need x permission on /home/labex
- You need x permission on /home/labex/mydata (to enter the directory)
- You need r permission on report.txt (to read the file itself)
What if you have r on the directory but not x?
If /home/labex/mydata has r-- permissions for "others" but not x, you could use ls /home/labex/mydata to see that report.txt exists (because you have read permission on the directory). However, you could not then cat /home/labex/mydata/report.txt because you lack the x (execute/traverse) permission on mydata to actually enter it and access its contents. You'd get "Permission denied".

So, to reiterate, the most fundamental permission for a directory to access anything inside it is the execute (x) permission for the appropriate user (owner, group, or others).

Does that clarify why x on a directory is so important for file access?