core-dumps

Name: core-dumps
Author: mohitmishra786

391installs19forks

How to install core-dumps?

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

$npx -y skills add mohitmishra786/low-level-dev-skills --skill core-dumps

Installs into the current project.

Summary

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

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SKILL.md

1	# Core Dumps
2
3	## Purpose
4
5	Guide agents through enabling, collecting, and analysing core dumps for post-mortem crash investigation without rerunning the buggy program.
6
7	## Triggers
8
9	- "My program crashed in production — how do I analyse the core?"
10	- "How do I enable core dumps on Linux?"
11	- "I have a core file but no symbols / source"
12	- "How do I use debuginfod to get symbols for a core?"
13	- "coredumpctl show me the crash"
14
15	## Workflow
16
17	### 1. Enable core dumps (Linux)
18
19	```bash
20	# Per-session (lost on logout)
21	ulimit -c unlimited
22
23	# Persistent (add to /etc/security/limits.conf)
24	* soft core unlimited
25	* hard core unlimited
26
27	# Check current limit
28	ulimit -c
29
30	# Set core pattern (where and how cores are named)
31	# Default: 'core' in CWD — often not useful
32	sudo sysctl -w kernel.core_pattern=/tmp/core-%e-%p-%t
33	# %e = executable, %p = PID, %t = timestamp
34
35	# Persistent (add to /etc/sysctl.d/99-core.conf)
36	kernel.core_pattern=/tmp/core-%e-%p-%t
37	kernel.core_uses_pid=1
38	```
39
40	### 2. systemd/coredumpctl (modern Linux)
41
42	If systemd manages core dumps (common on Ubuntu 20+, Fedora, Arch):
43
44	```bash
45	# List recent crashes
46	coredumpctl list
47
48	# Show details of the latest crash
49	coredumpctl info
50
51	# Load latest crash in GDB
52	coredumpctl gdb
53
54	# Load specific PID crash
55	coredumpctl gdb 12345
56
57	# Export core file
58	coredumpctl dump -o myapp.core PID
59	```
60
61	Core storage location: `/var/lib/systemd/coredump/`.
62
63	### 3. Enable core dumps (macOS)
64
65	```bash
66	# macOS uses /cores by default (must be root-writable)
67	ulimit -c unlimited
68
69	# Check
70	ls /cores/
71
72	# launchd-launched services: set in plist
73	# <key>HardResourceLimits</key>
74	# <dict><key>Core</key><integer>9223372036854775807</integer></dict>
75	```
76
77	### 4. Analyse a core with GDB
78
79	```bash
80	# Load binary and core
81	gdb ./prog core.12345
82
83	# If the binary was stripped, provide the unstripped copy
84	gdb ./prog-with-symbols core.12345
85
86	# Essential first commands
87	(gdb) bt # call stack
88	(gdb) bt full # stack + locals
89	(gdb) info registers # CPU state at crash
90	(gdb) frame 2 # jump to interesting frame
91	(gdb) info locals # local variables in frame
92	(gdb) print ptr # inspect a pointer
93
94	# All threads (multi-threaded crash)
95	(gdb) thread apply all bt full
96	```
97
98	### 5. Analyse a core with LLDB
99
100	```bash
101	lldb ./prog -c core.12345
102
103	# Or
104	lldb
105	(lldb) target create ./prog --core core.12345
106
107	# Commands
108	(lldb) bt
109	(lldb) thread backtrace all
110	(lldb) frame select 2
111	(lldb) frame variable
112	```
113
114	### 6. Missing symbols: debuginfod
115
116	`debuginfod` serves debug symbols from a central server, mapping build IDs to DWARF data.
117
118	```bash
119	# Install client (Debian/Ubuntu)
120	sudo apt install debuginfod
121
122	# Enable (add to ~/.bashrc or /etc/environment)
123	export DEBUGINFOD_URLS="https://debuginfod.ubuntu.com https://debuginfod.elfutils.org"
124
125	# GDB auto-fetches symbols when DEBUGINFOD_URLS is set
126	gdb ./prog core
127
128	# Manually query
129	debuginfod-find debuginfo <build-id>
130	debuginfod-find source <build-id> /path/to/file.c
131	```
132
133	### 7. Missing symbols: manual approach
134
135	```bash
136	# Check if binary has a build ID
137	readelf -n ./prog \| grep Build
138
139	# Find the correct debug package
140	# Debian: apt install prog-dbg or prog-dbgsym
141	# RPM: dnf install prog-debuginfo
142
143	# Point GDB to debug symbols directory
144	(gdb) set debug-file-directory /usr/lib/debug
145
146	# Or use eu-readelf to dump build ID, then find .debug file
147	eu-readelf -n ./prog
148	find /usr/lib/debug -name "*.debug" \| xargs eu-readelf -n 2>/dev/null \| grep <build-id>
149	```
150
151	### 8. Strip binaries and keep symbols
152
153	Best practice: build with symbols, strip for distribution, keep an unstripped copy.
154
155	```bash
156	# Build
157	gcc -g -O2 -o prog main.c
158
159	# Separate debug info
160	objcopy --only-keep-debug prog prog.debug
161	objcopy --strip-debug prog prog.stripped
162
163	# Add a debuglink so GDB finds the debug file automatically
164	objcopy --add-gnu-debuglink=prog.debug prog.stripped
165
166	# Deploy prog.stripped; keep prog.debug in a symbols store indexed by build-id
167	```
168
169	### 9. Quick triage from core without full debug session
170
171	```bash
172	# Print backtrace non-interactively
173	gdb -batch -ex 'bt full' -ex 'thread apply all bt full' ./prog core 2>&1 \| tee crash.txt
174
175	# Print registers
176	gdb -batch -ex 'info registers' ./prog core
177
178	# Check signal that caused crash
179	gdb -batch -ex 'info signal' ./prog core
180	```
181
182	For a full cheatsheet covering core pattern tokens, coredumpctl, GDB/LLDB commands, debuginfod servers, and strip/symbol workflows, see [references/cheatsheet.md](references/cheatsheet.md).
183
184	## Related skills
185
186	- Use `skills/debuggers/gdb` for full GDB session details
187	- Use `

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6 picks

Type

core-dumps

391installs19forks

View on GitHub

How to install core-dumps?

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

$npx -y skills add mohitmishra786/low-level-dev-skills --skill core-dumps

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	# Core Dumps
2
3	## Purpose
4
5	Guide agents through enabling, collecting, and analysing core dumps for post-mortem crash investigation without rerunning the buggy program.
6
7	## Triggers
8
9	- "My program crashed in production — how do I analyse the core?"
10	- "How do I enable core dumps on Linux?"
11	- "I have a core file but no symbols / source"
12	- "How do I use debuginfod to get symbols for a core?"
13	- "coredumpctl show me the crash"
14
15	## Workflow
16
17	### 1. Enable core dumps (Linux)
18
19	```bash
20	# Per-session (lost on logout)
21	ulimit -c unlimited
22
23	# Persistent (add to /etc/security/limits.conf)
24	* soft core unlimited
25	* hard core unlimited
26
27	# Check current limit
28	ulimit -c
29
30	# Set core pattern (where and how cores are named)
31	# Default: 'core' in CWD — often not useful
32	sudo sysctl -w kernel.core_pattern=/tmp/core-%e-%p-%t
33	# %e = executable, %p = PID, %t = timestamp
34
35	# Persistent (add to /etc/sysctl.d/99-core.conf)
36	kernel.core_pattern=/tmp/core-%e-%p-%t
37	kernel.core_uses_pid=1
38	```
39
40	### 2. systemd/coredumpctl (modern Linux)
41
42	If systemd manages core dumps (common on Ubuntu 20+, Fedora, Arch):
43
44	```bash
45	# List recent crashes
46	coredumpctl list
47
48	# Show details of the latest crash
49	coredumpctl info
50
51	# Load latest crash in GDB
52	coredumpctl gdb
53
54	# Load specific PID crash
55	coredumpctl gdb 12345
56
57	# Export core file
58	coredumpctl dump -o myapp.core PID
59	```
60
61	Core storage location: `/var/lib/systemd/coredump/`.
62
63	### 3. Enable core dumps (macOS)
64
65	```bash
66	# macOS uses /cores by default (must be root-writable)
67	ulimit -c unlimited
68
69	# Check
70	ls /cores/
71
72	# launchd-launched services: set in plist
73	# <key>HardResourceLimits</key>
74	# <dict><key>Core</key><integer>9223372036854775807</integer></dict>
75	```
76
77	### 4. Analyse a core with GDB
78
79	```bash
80	# Load binary and core
81	gdb ./prog core.12345
82
83	# If the binary was stripped, provide the unstripped copy
84	gdb ./prog-with-symbols core.12345
85
86	# Essential first commands
87	(gdb) bt # call stack
88	(gdb) bt full # stack + locals
89	(gdb) info registers # CPU state at crash
90	(gdb) frame 2 # jump to interesting frame
91	(gdb) info locals # local variables in frame
92	(gdb) print ptr # inspect a pointer
93
94	# All threads (multi-threaded crash)
95	(gdb) thread apply all bt full
96	```
97
98	### 5. Analyse a core with LLDB
99
100	```bash
101	lldb ./prog -c core.12345
102
103	# Or
104	lldb
105	(lldb) target create ./prog --core core.12345
106
107	# Commands
108	(lldb) bt
109	(lldb) thread backtrace all
110	(lldb) frame select 2
111	(lldb) frame variable
112	```
113
114	### 6. Missing symbols: debuginfod
115
116	`debuginfod` serves debug symbols from a central server, mapping build IDs to DWARF data.
117
118	```bash
119	# Install client (Debian/Ubuntu)
120	sudo apt install debuginfod
121
122	# Enable (add to ~/.bashrc or /etc/environment)
123	export DEBUGINFOD_URLS="https://debuginfod.ubuntu.com https://debuginfod.elfutils.org"
124
125	# GDB auto-fetches symbols when DEBUGINFOD_URLS is set
126	gdb ./prog core
127
128	# Manually query
129	debuginfod-find debuginfo <build-id>
130	debuginfod-find source <build-id> /path/to/file.c
131	```
132
133	### 7. Missing symbols: manual approach
134
135	```bash
136	# Check if binary has a build ID
137	readelf -n ./prog \| grep Build
138
139	# Find the correct debug package
140	# Debian: apt install prog-dbg or prog-dbgsym
141	# RPM: dnf install prog-debuginfo
142
143	# Point GDB to debug symbols directory
144	(gdb) set debug-file-directory /usr/lib/debug
145
146	# Or use eu-readelf to dump build ID, then find .debug file
147	eu-readelf -n ./prog
148	find /usr/lib/debug -name "*.debug" \| xargs eu-readelf -n 2>/dev/null \| grep <build-id>
149	```
150
151	### 8. Strip binaries and keep symbols
152
153	Best practice: build with symbols, strip for distribution, keep an unstripped copy.
154
155	```bash
156	# Build
157	gcc -g -O2 -o prog main.c
158
159	# Separate debug info
160	objcopy --only-keep-debug prog prog.debug
161	objcopy --strip-debug prog prog.stripped
162
163	# Add a debuglink so GDB finds the debug file automatically
164	objcopy --add-gnu-debuglink=prog.debug prog.stripped
165
166	# Deploy prog.stripped; keep prog.debug in a symbols store indexed by build-id
167	```
168
169	### 9. Quick triage from core without full debug session
170
171	```bash
172	# Print backtrace non-interactively
173	gdb -batch -ex 'bt full' -ex 'thread apply all bt full' ./prog core 2>&1 \| tee crash.txt
174
175	# Print registers
176	gdb -batch -ex 'info registers' ./prog core
177
178	# Check signal that caused crash
179	gdb -batch -ex 'info signal' ./prog core
180	```
181
182	For a full cheatsheet covering core pattern tokens, coredumpctl, GDB/LLDB commands, debuginfod servers, and strip/symbol workflows, see [references/cheatsheet.md](references/cheatsheet.md).
183
184	## Related skills
185
186	- Use `skills/debuggers/gdb` for full GDB session details
187	- Use `

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Type