Positions 2, 3, and 4

Specifying these bits is required. For each type of access—owner, group, and other—there is a corresponding octal number:

0: No access (---)
1: Execute-only access (--x)
2: Write-only access (-w-)
3: Write and execute access (-wx)
4: Read-only access (r--)
5: Read and execute access (r-x)
6: Read and write access (rw-)
7: Read, write, and execute access (rwx)

To specify permissions for a file or directory, you use at least a 3-digit octal number, omitting the digit in the first position. When you specify just three digits, the first digit describes owner permissions, the second digit describes group permissions, and the third digit describes permissions for all others. When the first digit is not set, some typical 3-digit permissions are specified in octal as shown in Figure 1.

Figure 1. Three-digit permissions specified in octal format

Examples of three-digit permissions that are specified in octal format.