Core Dumps

mohitmishra786/low-level-dev-skills/skills/debuggers/core-dumps

作者 mohitmishra786bdc58472fa9f無授權條款253 個星標收錄於 2026年10月9日更新於 2026年10月9日儲存庫3 個月前更新

Core dump analysis skill for production crash triage. Use when loading core files in GDB or LLDB, enabling core dump generation on Linux/macOS, mapping symbols with debuginfo or debuginfod, or extracting backtraces from crashes without re-running the program. Activates on queries about core files, ulimit, coredumpctl, debuginfod, crash triage, or analyzing segfaults from production binaries.

僅含說明Software DevelopmentDevOps & Cloud
AI 產生的概覽

引導代理啟用、收集並分析核心傾印，以便用 GDB、LLDB 和 debuginfod 進行事後當機排查。

功能
此技能提供在 Linux 與 macOS 上啟用核心傾印產生的逐步說明，包括 ulimit 設定、核心 core pattern 以及 systemd coredumpctl。內容涵蓋在 GDB 與 LLDB 中載入核心檔案、擷取呼叫堆疊、暫存器與區域變數，並透過 debuginfod 或手動除錯套件解析缺少的符號。它也說明如何用 objcopy 分離除錯資訊，以及以非互動批次方式做快速排查。工作流程附有一份參考速查表。
適用情境
當程式在正式環境當掉、需要在不重新執行程式的情況下分析核心檔案時使用。適用於有關核心檔案、ulimit、coredumpctl、debuginfod、當機排查或正式環境二進位檔段錯誤分析的問題。
執行需求
需要 GDB 或 LLDB 等除錯器，在 Linux 上可選用 systemd coredumpctl、debuginfod 用戶端工具、binutils（objcopy、readelf）與 elfutils。從 debuginfod 伺服器取得符號可能需要網路存取。此技能不附帶指令碼，只有說明與一份參考速查表。

Core Dumps

Purpose

Guide agents through enabling, collecting, and analysing core dumps for post-mortem crash investigation without rerunning the buggy program.

Triggers

  • "My program crashed in production — how do I analyse the core?"
  • "How do I enable core dumps on Linux?"
  • "I have a core file but no symbols / source"
  • "How do I use debuginfod to get symbols for a core?"
  • "coredumpctl show me the crash"

Workflow

1. Enable core dumps (Linux)

bash
# Per-session (lost on logout)ulimit -c unlimited
# Persistent (add to /etc/security/limits.conf)*   soft   core   unlimited*   hard   core   unlimited
# Check current limitulimit -c
# Set core pattern (where and how cores are named)# Default: 'core' in CWD — often not usefulsudo sysctl -w kernel.core_pattern=/tmp/core-%e-%p-%t# %e = executable, %p = PID, %t = timestamp
# Persistent (add to /etc/sysctl.d/99-core.conf)kernel.core_pattern=/tmp/core-%e-%p-%tkernel.core_uses_pid=1

2. systemd/coredumpctl (modern Linux)

If systemd manages core dumps (common on Ubuntu 20+, Fedora, Arch):

bash
# List recent crashescoredumpctl list
# Show details of the latest crashcoredumpctl info
# Load latest crash in GDBcoredumpctl gdb
# Load specific PID crashcoredumpctl gdb 12345
# Export core filecoredumpctl dump -o myapp.core PID

Core storage location: /var/lib/systemd/coredump/.

3. Enable core dumps (macOS)

bash
# macOS uses /cores by default (must be root-writable)ulimit -c unlimited
# Checkls /cores/
# launchd-launched services: set in plist# <key>HardResourceLimits</key># <dict><key>Core</key><integer>9223372036854775807</integer></dict>

4. Analyse a core with GDB

bash
# Load binary and coregdb ./prog core.12345
# If the binary was stripped, provide the unstripped copygdb ./prog-with-symbols core.12345
# Essential first commands(gdb) bt                    # call stack(gdb) bt full               # stack + locals(gdb) info registers        # CPU state at crash(gdb) frame 2               # jump to interesting frame(gdb) info locals           # local variables in frame(gdb) print ptr             # inspect a pointer
# All threads (multi-threaded crash)(gdb) thread apply all bt full

5. Analyse a core with LLDB

bash
lldb ./prog -c core.12345
# Orlldb(lldb) target create ./prog --core core.12345
# Commands(lldb) bt(lldb) thread backtrace all(lldb) frame select 2(lldb) frame variable

6. Missing symbols: debuginfod

debuginfod serves debug symbols from a central server, mapping build IDs to DWARF data.

bash
# Install client (Debian/Ubuntu)sudo apt install debuginfod
# Enable (add to ~/.bashrc or /etc/environment)export DEBUGINFOD_URLS="https://debuginfod.ubuntu.com https://debuginfod.elfutils.org"
# GDB auto-fetches symbols when DEBUGINFOD_URLS is setgdb ./prog core
# Manually querydebuginfod-find debuginfo <build-id>debuginfod-find source <build-id> /path/to/file.c

7. Missing symbols: manual approach

bash
# Check if binary has a build IDreadelf -n ./prog | grep Build
# Find the correct debug package# Debian: apt install prog-dbg or prog-dbgsym# RPM: dnf install prog-debuginfo
# Point GDB to debug symbols directory(gdb) set debug-file-directory /usr/lib/debug
# Or use eu-readelf to dump build ID, then find .debug fileeu-readelf -n ./progfind /usr/lib/debug -name "*.debug" | xargs eu-readelf -n 2>/dev/null | grep <build-id>

8. Strip binaries and keep symbols

Best practice: build with symbols, strip for distribution, keep an unstripped copy.

bash
# Buildgcc -g -O2 -o prog main.c
# Separate debug infoobjcopy --only-keep-debug prog prog.debugobjcopy --strip-debug prog prog.stripped
# Add a debuglink so GDB finds the debug file automaticallyobjcopy --add-gnu-debuglink=prog.debug prog.stripped
# Deploy prog.stripped; keep prog.debug in a symbols store indexed by build-id

9. Quick triage from core without full debug session

bash
# Print backtrace non-interactivelygdb -batch -ex 'bt full' -ex 'thread apply all bt full' ./prog core 2>&1 | tee crash.txt
# Print registersgdb -batch -ex 'info registers' ./prog core
# Check signal that caused crashgdb -batch -ex 'info signal' ./prog core

For a full cheatsheet covering core pattern tokens, coredumpctl, GDB/LLDB commands, debuginfod servers, and strip/symbol workflows, see references/cheatsheet.md [blocked].

Related skills

  • Use skills/debuggers/gdb for full GDB session details
  • Use skills/debuggers/lldb for LLDB-based analysis
  • Use skills/runtimes/sanitizers to catch the bug before it reaches production
  • Use skills/binaries/elf-inspection for readelf, build IDs, and binary inspection

來源與署名

來源：mohitmishra786/low-level-dev-skills位於skills/debuggers/core-dumps提交bdc5847

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