Q: A mission-critical C++ and Go payment gateway running inside Docker occasionally crashes with exit code 139 (`SIGSEGV` - Segmentation Fault). Because containers discard volatile state upon termination, no core dump file is produced, making postmortem debugging impossible. The development team is unable to locate the failing thread or memory address. You must configure the host kernel and container execution environment to capture full core dumps to a persistent host volume and analyze them using GDB.
Configure host Linux kernels and Docker containers to reliably generate core dumps during segmentation faults (`SIGSEGV`). Configure `/proc/sys/kernel/core_pattern`, ulimits, and debug with GDB.
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🛠️ Production Runbook & Step-by-Step Resolution
Understand Linux Kernel Core Pattern Mechanics for Containers
When a process crashes inside a container, the host kernel handles the core dump. If `/proc/sys/kernel/core_pattern` specifies a relative path (e.g., `core`), the file is written to the container's working directory and lost on container restart. To capture core dumps reliably, configure an absolute path on the host or pipe to a host handler.
# Configure host kernel core dump pattern to write to a dedicated host directory
echo '/var/coredumps/core.%e.%p.%h.%t' | sudo tee /proc/sys/kernel/core_pattern
# Ensure host directory exists and has permissive write permissions
sudo mkdir -p /var/coredumps && sudo chmod 1777 /var/coredumpsEnable Unlimited Core File Size in Docker Container
By default, Docker containers have a core dump ulimit of 0 (`ulimit -c 0`), which suppresses core dump generation. Pass `--ulimit core=-1:-1` at runtime to allow unlimited core dump sizes.
# Run container with unlimited core file size
docker run -d \
--name payment-engine \
--ulimit core=-1:-1 \
-v /var/coredumps:/var/coredumps \
payment-gateway:v3.2Simulate Crash and Verify Core Dump Generation
Send `SIGSEGV` or `SIGABRT` to the running process inside the container. Verify that the Linux kernel generates a complete memory image in `/var/coredumps`.
# Send SIGSEGV to trigger segmentation fault
docker exec -it payment-engine kill -SIGSEGV 1
# Verify core dump file on host
ls -lh /var/coredumps/
# Output: -rw------- 1 1000 1000 482M Oct 06 12:00 core.payment-engine.1.container-host.1728216000Inspect Stack Trace with GDB Inside Debug Container
Launch an ephemeral debugging container with GDB and debug symbols to inspect the backtrace and locate the exact crash line.
# Launch GDB to inspect thread backtrace
docker run --rm -v /var/coredumps:/dumps -v $(pwd)/symbols:/symbols ubuntu:22.04 \
gdb /symbols/payment-engine /dumps/core.payment-engine... -ex "bt full" -ex "quit"- W
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