Chmod 400 (r--------) Linux File Permission Explained
Complete breakdown of Unix/Linux chmod 400 (-r--------): binary bitmask, owner/group/public permissions, and security best practices (AWS PEM Key Pair Certificate Mode). (Chmod 400 Symbolic String: -r-------- | Access Scope: Owner Read-Only Immutable | Security)
Reviewed by: Alexei Volkov • Principal Systems & Cloud Infrastructure Architect
Methodology: Verified Formula
Key Quantitative Takeaway
Chmod 400 Symbolic String: -r-------- | Access Scope: Owner Read-Only Immutable | Security Classification: AWS PEM Key Pair Certificate Mode
Presets:
Chmod Command & Symbolic String
chmod 400 filename (-r--------)
Owner / Group / Public
r-- / --- / ---
Octal Notation
0400
Live Sensitivity Scale (Owner Octal (0-7: 4=Read, 2=Write, 1=Exec))
Output Comparison
0.75× Conservative
chmod 300 filename (--wx------)
1.00× Active
chmod 400 filename (-r--------)
1.50× Aggressive
chmod 600 filename (-rw-------)
755 is standard for web directories/scripts; 644 for static files.
Interactive Unix rwx Permission Bit Matrix (Click to Toggle)
Owner (User)
Group
Public (Others)
In-Depth Analysis — Chmod 400 (r--------) Linux File Permission Expl
Complete breakdown of Unix/Linux chmod 400 (-r--------): binary bitmask, owner/group/public permissions, and security best practices (AWS PEM Key Pair Certificate Mode).
Use the interactive Linux Chmod Octal (755, 644) & Symbolic Permission Calculator above to model custom production workloads and export CSV benchmark reports.
Need to run custom scenarios from scratch? Open the master Linux Chmod Octal (755, 644) & Symbolic Permission Calculator →
Scenario Comparison & Benchmark Table (Chmod Calculator)
Compare how scaling Owner Octal (0-7: 4=Read, 2=Write, 1=Exec) affects your output (click any row to load those values into the calculator above):
| Owner Octal (0-7: 4=Read, 2=Write, 1=Exec) | Chmod Command & Symbolic String | Owner / Group / Public | Octal Notation |
|---|---|---|---|
| 2 | chmod 200 filename (--w-------) | -w- / --- / --- | 0200 |
| 3 | chmod 300 filename (--wx------) | -wx / --- / --- | 0300 |
| 4 (Baseline) | chmod 400 filename (-r--------) | r-- / --- / --- | 0400 |
| 5 | chmod 500 filename (-r-x------) | r-x / --- / --- | 0500 |
| 6 | chmod 600 filename (-rw-------) | rw- / --- / --- | 0600 |
| 7 | chmod 700 filename (-rwx------) | rwx / --- / --- | 0700 |
Mathematical Formula & Step-by-Step Guide
Primary mathematical equation used by this model:
4 = Read (r), 2 = Write (w), 1 = Execute (x), 0 = None (-)
- Enter your Owner Octal (0-7: 4=Read, 2=Write, 1=Exec) and Group Octal (0-7) (or load 755 (Web Dir / Script), 644 (Standard HTML/Config), 600 (Private SSH Key) with one click) to establish your baseline scenario.
- Adjust Public / Others Octal (0-7) to see how the primary result and visual breakdown bar respond in real time.
- Scan the 6-tier Chmod Calculator Reference Benchmark Table below or click Download CSV / Print PDF to save your analysis.
Primary Standards & References: IETF RFC 8259 (JSON), RFC 4648 (Base64), RFC 9562 (UUIDv4), IEEE 802.3 / CIDR RFC 4632, POSIX.1-2017 File Permissions & Official 2026 LLM Tokenizer Pricing
All encoding, formatting, and cryptographic operations execute 100% locally in your browser via Web Crypto & V8 APIs—zero payload data leaves your device.
All encoding, formatting, and cryptographic operations execute 100% locally in your browser via Web Crypto & V8 APIs—zero payload data leaves your device.
Frequently Asked Questions — Chmod Calculator
How do you calculate Chmod 755 vs 644 vs 777 Guide (Linux File Permissions Security Guide)?
Use chmod 755 (rwxr-xr-x) for executable scripts and web directories, chmod 644 (rw-r--r--) for static HTML/config files, and chmod 600 (rw-------) for private SSH keys and .env secrets. You can also open our dedicated guide (Chmod 755 vs 644 vs 777 Guide) or click the preset buttons above to test this exact configuration interactively.
How do I optimize Owner Octal (0-7: 4=Read, 2=Write, 1=Exec) and Group Octal (0-7) for better Chmod Calculator performance?
At the default benchmark (Owner Octal (0-7: 4=Read, 2=Write, 1=Exec): 7, Group Octal (0-7): 5), balancing both inputs prevents bottlenecks and wasted budget. Test the built-in presets above to compare standard industry tiers.
What technical specification backs the Chmod Calculator calculation?
This tool implements 4 = Read (r), 2 = Write (w), 1 = Execute (x), 0 = None (-) in accordance with IETF RFC 8259 (JSON), RFC 4648 (Base64), RFC 9562 (UUIDv4), IEEE 802.3 / CIDR RFC 4632, POSIX.1-2017 File Permissions & Official 2026 LLM Tokenizer Pricing and is audited by Alexei Volkov • Principal Systems & Cloud Infrastructure Architect. You can export the full benchmark table as CSV or share a pre-filled URL parameter link with your team.