Linux permissions basics

Ls -l to output the below info.

Access rights on files.

  • r (or -), indicates read permission (or otherwise), that is, the presence or absence of permission to read and copy the file 
  • w (or -), indicates write permission (or otherwise), that is, the permission (or otherwise) to change a file 
  • x (or -), indicates execution permission (or otherwise), that is, the permission to execute a file, where appropriate

Access rights on directories.

  • r allows users to list files in the directory;
  • w means that users may delete files from the directory or move files into it;
  • x means the right to access files in the directory. This implies that you may read files in the directory provided you have read permission on the individual files.

So, in order to read a file, you must have execute permission on the directory containing that file, and hence on any directory containing that directory as a subdirectory, and so on, up the tree.

Some examples

-rwxrwxrwxa file that everyone can read, write and execute (and delete).
-rw——-a file that only the owner can read and write – no-one else  can read or write and no-one has execution rights (e.g. your  mailbox file).

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