Octal Number System Guide
Understanding the base-8 number system and its applications.
What is Octal?
The octal number system uses 8 digits (0-7). Each position represents a power of 8. It was historically popular in computing because each octal digit maps exactly to 3 binary digits, making conversions simple. Today it is mainly used for Unix/Linux file permissions.
Unix File Permissions
7 (111) = Read + Write + Execute
6 (110) = Read + Write
5 (101) = Read + Execute
4 (100) = Read only
3 (011) = Write + Execute
2 (010) = Write only
1 (001) = Execute only
0 (000) = No permissions
Example: chmod 755 = Owner(rwx) Group(r-x) Others(r-x)
Octal to Binary Quick Reference
0
000
1
001
2
010
3
011
4
100
5
101
6
110
7
111