Access Permissions   «Prev 

Meaning of access permission bits

The permission bits have the following significance for files:
  1. Read (r) permission means that the file contents may be read.
  2. Write (w) permission means that the file contents may be altered (so that, for example, the file may be appended to, overwritten, or truncated). Note that deleting a file involves write permission on the directory, not the file itself.
  3. Execute (x) permission means that the file may be loaded and executed (assuming that it is a program file).

The permission bits have the following significance for directories:
  1. Read (r) permission means that the directory contents may be read from the disk. Therefore, the filenames in the directory can be listed.
  2. Write (w) permission means that the directory may be altered. In particular, you can delete files from the directory or rename files in the directory.
  3. Execute (x) permission means you can make this directory your current directory. More important, execute permission means that you can search the directory. You cannot access a directory at all unless you have execute permission for every directory higher in the path of a given directory. Without execute permission in the given directory, you can list only the filenames in the directory.

Octal numbers and meanings for a user of a file


Octal Number Meaning
0 0 0 0 No permission
1 0 0 1 Execute permission, no read and write permissions
2 0 1 0 Write permission, no read and execute permissions
3 0 1 1 Write and execute permissions, no read permission
4 1 0 0 Read permission, no write and execute permissions
5 1 0 1 Read and execute permissions, no write permission
6 1 1 0 Read and write permissions, no execute permission
7 1 1 1 Read, write and execute permissions