docs: improve compressed core file documentation

[vpp.git] / docs / troubleshooting / reportingissues / reportingissues.rst

diff --git a/docs/troubleshooting/reportingissues/reportingissues.rst b/docs/troubleshooting/reportingissues/reportingissues.rst
index 73b2397..9192e20 100644 (file)
--- a/docs/troubleshooting/reportingissues/reportingissues.rst
+++ b/docs/troubleshooting/reportingissues/reportingissues.rst
@@ -198,9 +198,16 @@ If you start VPP from systemd, you also need to edit
 /lib/systemd/system/vpp.service and uncomment the "LimitCORE=infinity"
 line before restarting VPP.
 
-Vpp core files often appear enormous. Gzip typically compresses them
-to manageable sizes. A multi-GByte corefile often compresses to 10-20
-Mbytes.
+Vpp core files often appear enormous, but they are invariably
+sparse. Gzip compresses them to manageable sizes. A multi-GByte
+corefile often compresses to 10-20 Mbytes.
+
+When decompressing a vpp core file, we suggest using "dd" as shown to
+create a sparse, uncompressed core file:
+
+.. code-block:: console
+
+   $ zcat vpp_core.gz | dd conv=sparse of=vpp_core
 
 Please remember to put compressed core files in accessible places.
 
@@ -209,6 +216,9 @@ Make sure to leave the default stanza "... unix { ... full-coredump
 /etc/vpp/startup.conf, or to include it in the command line arguments
 passed by orchestration software.
 
+Core files from Private Images
+==============================
+
 Core files from private images require special handling. If it's
 necessary to go that route, copy the **exact** Debian packages (or
 RPMs) which correspond to the core file to the same public place as
@@ -238,6 +248,33 @@ Even given a byte-for-byte identical source tree, it's easy to build
 dramatically different binary artifacts. All it takes is a different
 toolchain version.
 
+
+On-the-fly Core File Compression
+--------------------------------
+
+Depending on operational requirements, it's possible to compress
+corefiles as they are generated. Please note that it takes several
+seconds' worth of wall-clock time to compress a vpp core file on the
+fly, during which all packet processing activities are suspended.
+
+To create compressed core files on the fly, create the following
+script, e.g. in /usr/local/bin/compressed_corefiles, owned by root,
+executable:
+
+.. code-block:: console
+
+  #!/bin/sh
+  exec /bin/gzip -f - >"/tmp/dumps/core-$1.$2.gz"
+
+Adjust the kernel core file pattern as shown:
+
+.. code-block:: console
+
+  sysctl -w kernel.core_pattern="|/usr/local/bin/compressed_corefiles %e %t"
+
+Core File Summary
+-----------------
+
 Bottom line: please follow core file handling instructions to the
 letter. It's not complicated. Simply copy the exact Debian packages or
 RPMs which correspond to core files to accessible locations.