Linux Kernel Crash Debugging

---

name: linux-kernel-crash-debug

description: Debug Linux kernel crashes using the crash utility. Use when users mention kernel crash, kernel panic, vmcore analysis, kernel dump debugging, crash utility, kernel oops debugging, analyzing kernel crash dump files, using crash commands, or locating root causes of kernel issues.

requires:

- crash

- gdb

- readelf

- objdump

- makedumpfile

---

# Linux Kernel Crash Debugging

This skill guides you through analyzing Linux kernel crash dumps using the crash utility.

Installation

Claude Code

claude skill install linux-kernel-crash-debug.skill

OpenClaw

# Method 1: Install via ClawHub
clawhub install linux-kernel-crash-debug

# Method 2: Manual installation
mkdir -p ~/.openclaw/workspace/skills/linux-kernel-crash-debug
cp SKILL.md ~/.openclaw/workspace/skills/linux-kernel-crash-debug/

Quick Start

Starting a Session

# Analyze a dump file
crash vmlinux vmcore

# Debug a running system
crash vmlinux

# Raw RAM dump
crash vmlinux ddr.bin --ram_start=0x80000000

Core Debugging Workflow

1. crash> sys              # Confirm panic reason
2. crash> log              # View kernel log
3. crash> bt               # Analyze call stack
4. crash> struct <type>    # Inspect data structures
5. crash> kmem <addr>      # Memory analysis

Prerequisites

| Item | Requirement |

|------|-------------|

| **vmlinux** | Must have debug symbols (`CONFIG_DEBUG_INFO=y`) |

| **vmcore** | kdump/netdump/diskdump/ELF format |

| **Version** | vmlinux must exactly match the vmcore kernel version |

Package Installation

#### Anolis OS / Alibaba Cloud Linux

# Install crash utility
sudo dnf install crash

# Install kernel debuginfo (match your kernel version)
sudo dnf install kernel-debuginfo-$(uname -r)

# Install additional analysis tools
sudo dnf install gdb readelf objdump makedumpfile

# Optional: Install kernel-devel for source code reference
sudo dnf install kernel-devel-$(uname -r)

#### RHEL / CentOS / Rocky / AlmaLinux

sudo dnf install crash kernel-debuginfo-$(uname -r)
sudo dnf install gdb binutils makedumpfile

#### Ubuntu / Debian

sudo apt install crash linux-crashdump gdb binutils makedumpfile
sudo apt install linux-image-$(uname -r)-dbgsym

Self-compiled Kernel

# Enable debug symbols in kernel config
make menuconfig  # Enable CONFIG_DEBUG_INFO, CONFIG_DEBUG_INFO_REDUCED=n

# Or set directly
scripts/config --enable CONFIG_DEBUG_INFO
scripts/config --enable CONFIG_DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT

Verify Installation

# Check crash version
crash --version

# Verify debuginfo matches kernel
crash /usr/lib/debug/lib/modules/$(uname -r)/vmlinux /proc/kcore

Core Command Reference

Debugging Analysis

| Command | Purpose | Example |

|---------|---------|---------|

| `sys` | System info/panic reason | `sys`, `sys -i` |

| `log` | Kernel message buffer | `log`, `log \| tail` |

| `bt` | Stack backtrace | `bt`, `bt -a`, `bt -f` |

| `struct` | View structures | `struct task_struct <addr>` |

| `p/px/pd` | Print variables | `p jiffies`, `px current` |

| `kmem` | Memory analysis | `kmem -i`, `kmem -S <cache>` |

Tasks and Processes

| Command | Purpose | Example |

|---------|---------|---------|

| `ps` | Process list | `ps`, `ps -m \| grep UN` |

| `set` | Switch context | `set <pid>`, `set -p` |

| `foreach` | Batch task operations | `foreach bt`, `foreach UN bt` |

| `task` | task_struct contents | `task <pid>` |

| `files` | Open files | `files <pid>` |

Memory Operations

| Command | Purpose | Example |

|---------|---------|---------|

| `rd` | Read memory | `rd <addr>`, `rd -p <phys>` |

| `search` | Search memory | `search -k deadbeef` |

| `vtop` | Address translation | `vtop <addr>` |

| `list` | Traverse linked lists | `list task_struct.tasks -h <addr>` |

bt Command Details

The most important debugging command:

crash> bt              # Current task stack
crash> bt -a           # All CPU active tasks
crash> bt -f           # Expand stack frame raw data
crash> bt -F           # Symbolic stack frame data
crash> bt -l           # Show source file and line number
crash> bt -e           # Search for exception frames
crash> bt -v           # Check stack overflow
crash> bt -R <sym>     # Only show stacks referencing symbol
crash> bt <pid>        # Specific process

Context Management

Crash session has a "current context" affecting `bt`, `files`, `vm` commands:

crash> set              # View current context
crash> set <pid>        # Switch to specified PID
crash> set <task_addr>  # Switch to task address
crash> set -p           # Restore to panic task

Session Control

# Output control
crash> set scroll off   # Disable pagination
crash> sf               # Alias for scroll off

# Output redirection
crash> foreach bt > bt.all

# GDB passthrough
crash> gdb bt           # Single gdb invocation
crash> set gdb on       # Enter gdb mode
(gdb) info registers
(gdb) set gdb off

# Read commands from file
crash> < commands.txt

Typical Debugging Scenarios

Kernel BUG Location

crash> sys                    # Confirm panic
crash> log | tail -50         # View logs
crash> bt                     # Call stack
crash> bt -f                  # Expand frames for parameters
crash> struct <type> <addr>   # Inspect data structures

Deadlock Analysis

crash> bt -a                  # All CPU call stacks
crash> ps -m | grep UN        # Uninterruptible processes
crash> foreach UN bt          # View waiting reasons
crash> struct mutex <addr>    # Inspect lock state

Memory Issues

crash> kmem -i                # Memory statistics
crash> kmem -S <cache>        # Inspect slab
crash> vm <pid>               # Process memory mapping
crash> search -k <pattern>    # Search memory

Stack Overflow

crash> bt -v                  # Check stack overflow
crash> bt -r                  # Raw stack data

Advanced Techniques

Chained Queries

crash> bt -f                  # Get pointers
crash> struct file.f_dentry <addr>
crash> struct dentry.d_inode <addr>
crash> struct inode.i_pipe <addr>

Batch Slab Inspection

crash> kmem -S inode_cache | grep counter | grep -v "= 1"

Kernel Linked List Traversal

crash> list task_struct.tasks -s task_struct.pid -h <start>
crash> list -h <addr> -s dentry.d_name.name

Extended Reference

For detailed information, refer to the following reference files:

| File | Content |

|------|---------|

| `references/advanced-commands.md` | Advanced commands: list, rd, search, vtop, kmem, foreach |

| `references/vmcore-format.md` | vmcore file format, ELF structure, VMCOREINFO |

| `references/case-studies.md` | Detailed debugging cases: kernel BUG, deadlock, OOM, NULL pointer, stack overflow |

Usage:

crash> help <command>        # Built-in help
# Or ask Claude to view reference files

Common Errors

crash: vmlinux and vmcore do not match!
# -> Ensure vmlinux version exactly matches vmcore

crash: cannot find booted kernel
# -> Specify vmlinux path explicitly

crash: cannot resolve symbol
# -> Check if vmlinux has debug symbols

Security Warnings

⚠️ **Dangerous Operations**

The following commands can cause system damage or data loss:

| Command | Risk | Recommendation |

|---------|------|----------------|

| `wr` | Writes to live kernel memory | **NEVER use on production systems** - can crash or corrupt running kernel |

| GDB passthrough | Unrestricted memory access | Use with caution, may modify memory or registers |

🔒 **Sensitive Data Handling**

- User process memory and credentials

- Encryption keys and secrets

- Network connection data and passwords

🛡️ **Best Practices**

1. Only analyze vmcore files in isolated/test environments when possible

2. Never share raw vmcore files publicly without sanitization

3. Consider using `makedumpfile -d` to filter sensitive pages before analysis

4. Document and audit all crash analysis sessions for compliance

Important Notes

1. **Version Match**: vmlinux must exactly match the vmcore kernel version

2. **Debug Info**: Must use vmlinux with debug symbols

3. **Context Awareness**: `bt`, `files`, `vm` commands are affected by current context

4. **Live System Modification**: `wr` command modifies running kernel, extremely dangerous

Resources

Contributing

This is an open-source project. Contributions are welcome!

See [CONTRIBUTING.md](https://github.com/crazyss/linux-kernel-crash-debug/blob/main/CONTRIBUTING.md) for guidelines.