---
id: php-sessions
title: "PHP Sessions"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["session_start()", "$_SESSION", "PHP 세션"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.9
created_at: 2026-07-04
updated_at: 2026-07-04
review_reason: ""
merge_history: []
tags: ["php", "programming", "w3schools", "sessions"]
raw_sources: ["https://www.w3schools.com/php/php_sessions.asp"]
applied_in: []
github_commit: ""
---

# [[PHP Sessions]]

## 🎯 한 줄 통찰 (One-line insight)
A session's ONLY client-side footprint is a small random ID stored in a `PHPSESSID` cookie — the actual session DATA lives entirely on the server (typically in a temp file), meaning sessions are fundamentally more secure than cookies for sensitive data, since the browser never holds the real information, just a lookup key. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Session** — solves HTTP's statelessness by storing per-user data server-side, linked via a client-side ID cookie. [S1]
- **`session_start()`** — must be called at the very beginning of every script using sessions, before ANY HTML output or whitespace. [S1]
- **`$_SESSION`** — superglobal for storing/accessing session variables. [S1]
- **`unset($_SESSION["key"])`** — removes one session variable. [S1]
- **`session_unset()`** — clears ALL session variables. [S1]
- **`session_destroy()`** — destroys all data tied to the current session entirely. [S1]
- **Default lifetime** — session data persists until the browser closes (unlike cookies, which can have a long fixed expiration). [S1]
- **Sessions vs. cookies** — sessions: server-stored, more secure, closes-on-browser-close, more efficient (no repeated data transfer); cookies: browser-stored, less secure, long expiration possible, less efficient (sent with every request). [S1]

## 📖 세부 내용 (Details)
- Start + set variables: `session_start(); $_SESSION["favcolor"] = "green"; $_SESSION["favanimal"] = "cat";`. [S1]
- Retrieve on another page: `session_start(); if(isset($_SESSION["favcolor"])) { echo $_SESSION["favcolor"]; }`. [S1]
- Modify: overwrite directly — `$_SESSION["favcolor"] = "yellow";`. [S1]
- Destroy (logout): `session_start(); session_unset(); session_destroy(); echo "You have been logged out.";`. [S1]
- Debug all values: `print_r($_SESSION);`. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
소스에서 모순되는 정보는 발견되지 않음.

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — session_unset()+session_destroy() 조합으로 로그아웃을 구현하는 것이 실전 인증 시스템의 표준 패턴이다. [S1]

## 💻 코드 패턴 (Code patterns)
Logging out by clearing all session data (PHP):
```php
session_start();
session_unset();
session_destroy();
echo "You have been logged out.";
```

## ✅ 검증 상태 및 신뢰도
- **상태:** draft
- **검증 단계:** conceptual
- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
- **신뢰 점수:** 0.90
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[PHP Tutorial]]
- **관련 개념:** [[PHP Cookies]], [[PHP Filter]]
- **참조 맥락:** 서버 측 사용자 데이터 저장 — 필터(Filter) 섹션으로 이어짐.

## 📚 출처 (Sources)
- [S1] W3Schools — PHP Sessions — https://www.w3schools.com/php/php_sessions.asp

## 📝 변경 이력 (Change history)
- 2026-07-04: Initial draft synthesized from the W3Schools "PHP Sessions" page (Astra wiki-curation, P-Reinforce v3.1 format).