Add critical grub2-mkconfig composefs compatibility fix
- Add comprehensive fix for grub2-mkconfig composefs incompatibility - Document the critical issue from Red Hat Bugzilla #2308594 - Provide complete patch, automated script, and Containerfile integration - Add troubleshooting documentation with verification steps - Update COMPATIBILITY.md with critical issue warning - Update README.md to highlight this critical fix This fix is ESSENTIAL for all composefs-based bootc images to boot properly. Without this fix, grub2-mkconfig will generate incorrect configurations and cause boot failures. Based on: - Red Hat Bugzilla #2308594 (reported by Colin Walters) - ostree issue #3198 - Affects all bootc/ostree systems using composefs
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troubleshooting/grub2-composefs-fix.md
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# grub2-mkconfig Composefs Compatibility Fix
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This document provides a critical fix for the incompatibility between `grub2-mkconfig` and composefs that affects all bootc images.
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## Problem Description
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**Issue**: `grub2-mkconfig` is incompatible with composefs and will cause boot failures in bootc images.
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**Root Cause**:
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- `grub2-mkconfig` doesn't know how to read `/sysroot` where the physical root filesystem lives
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- It tries to probe the overlay filesystem instead of the actual root filesystem
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- This results in incorrect grub configuration and boot failures
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**Reference**: [Red Hat Bugzilla #2308594](https://bugzilla.redhat.com/show_bug.cgi?id=2308594) - Reported by Colin Walters (ostree maintainer)
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## The Fix
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### Step 1: Backup Original File
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```bash
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sudo cp /usr/sbin/grub2-mkconfig /usr/sbin/grub2-mkconfig.backup
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```
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### Step 2: Apply the Patch
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Edit `/usr/sbin/grub2-mkconfig` and add this code after line 138:
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```bash
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# Path to the real rootfs; we may be in a container or using bootc/ostree
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GRUB_PHYSICAL_FILESYSTEM=/
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GRUB_FS="$(stat -f -c %T / || echo unknown)"
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if test "x${GRUB_FS}" = "xoverlay" && test -d /sysroot; then
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GRUB_PHYSICAL_FILESYSTEM=/sysroot
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fi
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```
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### Step 3: Update Device Detection
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Find this line (around line 145):
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```bash
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GRUB_DEVICE="`${grub_probe} --target=device /`"
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```
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Replace it with:
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```bash
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GRUB_DEVICE="`${grub_probe} --target=device ${GRUB_PHYSICAL_FILESYSTEM}`"
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```
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### Step 4: Test the Fix
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```bash
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# Test grub2-mkconfig
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sudo grub2-mkconfig -o /boot/grub2/grub.cfg
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# Verify it detects the correct filesystem
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echo "Physical filesystem: ${GRUB_PHYSICAL_FILESYSTEM}"
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```
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## Complete Patch
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Here's the complete patch to apply:
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```diff
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--- /usr/sbin/grub2-mkconfig.orig 2024-08-29 20:29:13.483212450 +0000
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+++ /usr/sbin/grub2-mkconfig 2024-08-29 20:28:36.605582110 +0000
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@@ -138,8 +138,15 @@
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exit 1
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fi
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+# Path to the real rootfs; we may be in a container or using bootc/ostree
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+GRUB_PHYSICAL_FILESYSTEM=/
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+GRUB_FS="$(stat -f -c %T / || echo unknown)"
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+if test "x${GRUB_FS}" = "xoverlay" && test -d /sysroot; then
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+ GRUB_PHYSICAL_FILESYSTEM=/sysroot
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+fi
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+
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# Device containing our userland. Typically used for root= parameter.
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-GRUB_DEVICE="`${grub_probe} --target=device /`"
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+GRUB_DEVICE="`${grub_probe} --target=device ${GRUB_PHYSICAL_FILESYSTEM}`"
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GRUB_DEVICE_UUID="`${grub_probe} --device ${GRUB_DEVICE} --target=fs_uuid 2> /dev/null`" || true
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GRUB_DEVICE_PARTUUID="`${grub_probe} --device ${GRUB_DEVICE} --target=partuuid 2> /dev/null`" || true
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```
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## Automated Fix Script
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Create a script to apply the fix automatically:
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```bash
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#!/bin/bash
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# grub2-composefs-fix.sh
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set -euo pipefail
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GRUB_MKCONFIG="/usr/sbin/grub2-mkconfig"
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BACKUP_FILE="${GRUB_MKCONFIG}.backup"
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echo "🔧 Applying grub2-mkconfig composefs compatibility fix..."
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# Backup original file
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if [ ! -f "$BACKUP_FILE" ]; then
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echo "📋 Creating backup: $BACKUP_FILE"
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sudo cp "$GRUB_MKCONFIG" "$BACKUP_FILE"
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fi
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# Create temporary file with fix
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TEMP_FILE=$(mktemp)
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sudo cp "$GRUB_MKCONFIG" "$TEMP_FILE"
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# Apply the fix
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sed -i '138a\
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# Path to the real rootfs; we may be in a container or using bootc/ostree\
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GRUB_PHYSICAL_FILESYSTEM=/\
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GRUB_FS="$(stat -f -c %T / || echo unknown)"\
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if test "x${GRUB_FS}" = "xoverlay" && test -d /sysroot; then\
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GRUB_PHYSICAL_FILESYSTEM=/sysroot\
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fi\
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' "$TEMP_FILE"
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# Update device detection line
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sed -i 's|GRUB_DEVICE="`${grub_probe} --target=device /`"|GRUB_DEVICE="`${grub_probe} --target=device ${GRUB_PHYSICAL_FILESYSTEM}`"|' "$TEMP_FILE"
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# Replace original file
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sudo mv "$TEMP_FILE" "$GRUB_MKCONFIG"
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sudo chmod +x "$GRUB_MKCONFIG"
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echo "✅ Fix applied successfully!"
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echo "🧪 Testing grub2-mkconfig..."
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# Test the fix
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if sudo grub2-mkconfig -o /tmp/grub-test.cfg 2>/dev/null; then
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echo "✅ grub2-mkconfig test passed!"
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rm -f /tmp/grub-test.cfg
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else
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echo "❌ grub2-mkconfig test failed!"
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echo "🔄 Restoring backup..."
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sudo mv "$BACKUP_FILE" "$GRUB_MKCONFIG"
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exit 1
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fi
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echo "🎉 grub2-mkconfig composefs fix completed successfully!"
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```
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## Integration in Base Images
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Add this fix to your base image Containerfile:
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```dockerfile
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# Apply grub2-mkconfig composefs fix
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RUN sed -i '138a\
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# Path to the real rootfs; we may be in a container or using bootc/ostree\
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GRUB_PHYSICAL_FILESYSTEM=/\
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GRUB_FS="$(stat -f -c %T / || echo unknown)"\
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if test "x${GRUB_FS}" = "xoverlay" && test -d /sysroot; then\
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GRUB_PHYSICAL_FILESYSTEM=/sysroot\
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fi\
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' /usr/sbin/grub2-mkconfig
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RUN sed -i 's|GRUB_DEVICE="`${grub_probe} --target=device /`"|GRUB_DEVICE="`${grub_probe} --target=device ${GRUB_PHYSICAL_FILESYSTEM}`"|' /usr/sbin/grub2-mkconfig
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```
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## Verification
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After applying the fix, verify it works:
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```bash
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# Check if the fix is applied
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grep -A 5 "GRUB_PHYSICAL_FILESYSTEM" /usr/sbin/grub2-mkconfig
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# Test grub2-mkconfig
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sudo grub2-mkconfig -o /boot/grub2/grub.cfg
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# Check for errors
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echo $?
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```
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## Troubleshooting
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### Common Issues
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1. **Permission denied**: Run with `sudo`
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2. **File not found**: Check if `grub2-mkconfig` exists at `/usr/sbin/grub2-mkconfig`
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3. **Syntax error**: Verify the sed commands are applied correctly
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4. **Test fails**: Check if `/sysroot` exists and is accessible
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### Rollback
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If the fix causes issues, restore the backup:
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```bash
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sudo mv /usr/sbin/grub2-mkconfig.backup /usr/sbin/grub2-mkconfig
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```
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## Impact
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This fix is **essential** for:
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- All composefs-based bootc images
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- Any system using ostree with composefs
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- Proper grub configuration generation
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- Successful boot process
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Without this fix, bootc images will fail to boot due to incorrect grub configuration.
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