Octal Unix Permissions — Learn

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About this interactive

What you're seeing: a guided walkthrough that converts Unix file permissions between symbolic notation (rwxr-xr-x) and octal (755), one slot at a time. Why it matters: chmod takes an octal value, ls -l shows you a symbolic string, and working on a Linux system means moving between the two without a lookup table — it works because each rwx triad is three bits, exactly one octal digit. How to use it: pick one triad or the full nine characters, step through the slots in Guided mode — adding 4, 2 and 1 for the bits that are on, or asking whether they fit in a digit — then switch to Solo and convert on your own.

What you'll learn

Convert a symbolic Unix permission triad or full nine-character string to octal by adding read = 4, write = 2 and execute = 1 within each triad
Convert an octal permission value back to symbolic notation, one rwx triad per octal digit

Aligned to

CompTIA Tech+

1.1 Compare and contrast notational systems.

3.2 Compare and contrast components of an operating system.

Key terms

Octal: A base-8 number system using digits 0 through 7, where each digit represents exactly three binary bits; commonly used in Unix and Linux file permission notation because a three-bit permission group (read, write, execute) maps cleanly to a single octal digit.
Octal Notation: A base-8 numbering system used in Unix/Linux to represent file permission settings as a three-digit value, where each digit corresponds to user, group, and other access levels.
Read, Write, Execute: The three permission types in Unix/Linux: read allows viewing a file, write allows modifying it, and execute allows running it as a program or traversing a directory.
Linux File Permissions: A permission model in Linux that assigns read, write, and execute rights separately to three categories: the owning user, the owning group, and all others.
chmod: A Unix/Linux command used to change the permission settings of a file or directory using symbolic or octal values.
File Permissions: Settings on a Unix/Linux file or directory that control read, write, and execute access for the owner, group, and all other users.
Binary: The base-2 number system that uses only the digits 0 and 1; the native language of digital computers, which store and process data as electrical on/off states.
Bit: Short for binary digit, the smallest unit of data in computing, holding a single value of 0 or 1; all digital information is ultimately composed of bits.

Topics

Octal Linux File Permissions Number Systems

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