mirror of
https://github.com/CyberMind-FR/secubox-deb.git
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CyberMind-FR
00766234d2
Kernel nftables fix (issue #64): - Added CONFIG_NF_TABLES_INET, CONFIG_NF_TABLES_IPV4/IPV6 - Added NFT_CT, NFT_LOG, NFT_LIMIT, NFT_REJECT, NFT_COUNTER - CrowdSec firewall bouncer now works correctly Build script safety: - Added deploy_to_device() with safe module extraction - Prevents /lib symlink overwrite disaster Documentation: - FAQ-BUSYBOX-RESCUE.md: Emergency recovery when libc inaccessible - PROMPT-BUSYBOX-TECHTIP.md: Gemini prompt for visual tech tip - QUICKSHEET: Added emergency recovery section Sidebar v2.32.0: - Per-LED tooltips (Hardware/Services/Security) - Fixed tooltip positioning for sidebar elements Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
151 lines
3.3 KiB
Markdown
151 lines
3.3 KiB
Markdown
# FAQ: Busybox Emergency Recovery
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## The Problem
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**Symptom:** All commands fail with "cannot execute: required file not found"
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```bash
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root@host:~# ls
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-bash: /usr/bin/ls: cannot execute: required file not found
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root@host:~# ln -s foo bar
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-bash: /usr/bin/ln: cannot execute: required file not found
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```
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**Cause:** The `/lib` symlink (pointing to `/usr/lib`) was replaced by a directory, breaking access to `libc.so` and the dynamic linker.
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**Common trigger:** Extracting a tarball containing `lib/` at root level:
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```bash
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# DANGEROUS - overwrites /lib symlink!
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cd / && tar xzf modules.tar.gz
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```
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---
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## The Solution: Busybox
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Busybox is typically **statically linked** - it doesn't need libc to run.
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### Step 1: Check if busybox exists
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```bash
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echo /bin/busybox
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echo /usr/bin/busybox
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```
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### Step 2: Use busybox to fix the symlink
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```bash
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# Remove broken /lib directory
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/bin/busybox rm -rf /lib
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# Recreate the symlink
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/bin/busybox ln -s usr/lib /lib
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# Verify
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/bin/busybox ls -la /lib
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```
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### Step 3: Test recovery
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```bash
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ls -la /lib/aarch64-linux-gnu/libc.so*
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cat /etc/os-release
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uname -r
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```
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---
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## Why This Works
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| Component | Location | Status when /lib broken |
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|-----------|----------|------------------------|
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| libc.so | `/usr/lib/aarch64-linux-gnu/` | Exists but inaccessible |
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| ld-linux | `/usr/lib/aarch64-linux-gnu/` | Exists but inaccessible |
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| /lib | Should be symlink to `usr/lib` | **Broken** - is a directory |
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| busybox | `/bin/busybox` | **Works** - statically linked |
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Busybox contains 300+ commands in a single static binary. When libc is inaccessible, it's your lifeline.
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---
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## Prevention
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### Safe tarball extraction for kernel modules:
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```bash
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# WRONG
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cd / && tar xzf modules.tar.gz
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# RIGHT - extract only the modules subdirectory
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tar xzf modules.tar.gz -C /lib/modules/ --strip-components=2
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# OR create tarball with correct structure
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cd /build/output/modules/lib/modules
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tar czf modules-6.6.137.tar.gz 6.6.137
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# Then on target:
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cd /lib/modules && tar xzf /tmp/modules-6.6.137.tar.gz
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```
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### Check before extracting:
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```bash
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# Always check tarball contents first!
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tar tzf modules.tar.gz | head -20
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# Look for dangerous top-level paths:
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# lib/ <- DANGER if extracted at /
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# usr/ <- DANGER
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# bin/ <- DANGER
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```
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---
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## Shell Built-ins When Nothing Works
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If no busybox available, bash built-ins still work:
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```bash
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# List files (glob expansion)
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echo /lib/*
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echo /usr/lib/aarch64-linux-gnu/libc*
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# Read file content
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while IFS= read -r line; do echo "$line"; done < /etc/os-release
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# Check if path exists
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[[ -d /lib/aarch64-linux-gnu ]] && echo "exists" || echo "missing"
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# Write to file
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echo "test" > /tmp/test
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```
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---
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## Last Resort: Rescue Boot
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If no busybox and shell built-ins can't help:
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1. Boot from USB/SD rescue media
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2. Mount the broken rootfs:
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```bash
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mount /dev/mmcblk0p2 /mnt
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```
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3. Fix the symlink:
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```bash
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rm -rf /mnt/lib
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ln -s usr/lib /mnt/lib
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```
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4. Reboot normally
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---
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## Key Takeaways
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1. **Always have busybox installed** (statically linked)
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2. **Never extract tarballs blindly at /**
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3. **Check tarball contents before extracting**
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4. **Know your shell built-ins** (echo, read, [[ ]])
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5. **Keep rescue media ready** for emergencies
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---
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*SecuBox-Deb Emergency Recovery Guide*
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*CyberMind — https://cybermind.fr*
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*Author: Gerald Kerma <gandalf@gk2.net>*
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*Incident: 2026-05-08*
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