docs: how to enable coredump with systemd

Type: docs

Change-Id: I1f657389fec716cc6cdc942803e65f861ffea5f5
Signed-off-by: Benoît Ganne <bganne@cisco.com>
diff --git a/docs/troubleshooting/reportingissues/reportingissues.rst b/docs/troubleshooting/reportingissues/reportingissues.rst
index 261dec9..73b2397 100644
--- a/docs/troubleshooting/reportingissues/reportingissues.rst
+++ b/docs/troubleshooting/reportingissues/reportingissues.rst
@@ -194,6 +194,10 @@
     # ulimit -c unlimited
     # echo 2 > /proc/sys/fs/suid_dumpable
 
+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.