Bug 177188

Summary:	dumpon(8) unaware of mini crash dumps
Product:	Documentation	Reporter:	Fabian Keil <fk>
Component:	Books & Articles	Assignee:	Joel Dahl <joel>
Status:	Closed FIXED
Severity:	Affects Only Me	CC:	kkimdavenport
Priority:	Normal
Version:	Latest
Hardware:	Any
OS:	Any

Description Fabian Keil 2013-03-21 11:40:01 UTC

dumpon(8) currently states:

| The dumpon utility will refuse to enable a dump device which is smaller
| than the total amount of physical memory as reported by the hw.physmem
| sysctl(8) variable.

If mini crash dumps are enabled smaller dump devices are actually accepted.

It might also be worth mentioning that with mini crash dumps disabled no error message is printed unless -v is used.

Fix: 

Update the man page.
How-To-Repeat: fk@r500 ~ $sysctl debug.minidump
debug.minidump: 1
fk@r500 ~ $sysctl kern.shutdown.dumpdevname
kern.shutdown.dumpdevname: 
fk@r500 ~ $sysctl hw.physmem
hw.physmem: 2070306816
fk@r500 ~ $diskinfo -v /dev/da0 | grep bytes
	750780416   	# mediasize in bytes (716M)
fk@r500 ~ $sudo dumpon /dev/da0
fk@r500 ~ $echo $?
0
fk@r500 ~ $sysctl kern.shutdown.dumpdevname
kern.shutdown.dumpdevname: da0
fk@r500 ~ $sudo dumpon off
fk@r500 ~ $sudo sysctl debug.minidump=0
debug.minidump: 1 -> 0
fk@r500 ~ $sudo dumpon /dev/da0
fk@r500 ~ $echo $?
74
fk@r500 ~ $sudo dumpon -v /dev/da0
/dev/da0 is smaller than physical memory

Comment 1 Joel Dahl freebsd_committer

2013-04-24 08:50:52 UTC

Responsible Changed
From-To: freebsd-doc->joel

Take

Comment 2 Joel Dahl freebsd_committer

2013-04-30 08:22:24 UTC

State Changed
From-To: open->closed

I've updated the man page and I'm closing this PR. Thanks!

Comment 3 dfilter service freebsd_committer

2013-04-30 08:22:26 UTC

Author: joel (doc committer)
Date: Tue Apr 30 07:22:03 2013
New Revision: 250095
URL: http://svnweb.freebsd.org/changeset/base/250095

Log:
  Adapt to the fact that minidumps are now on by default.
  
  PR:		177188

Modified:
  head/sbin/dumpon/dumpon.8

Modified: head/sbin/dumpon/dumpon.8
==============================================================================
--- head/sbin/dumpon/dumpon.8	Tue Apr 30 06:41:42 2013	(r250094)
+++ head/sbin/dumpon/dumpon.8	Tue Apr 30 07:22:03 2013	(r250095)
@@ -28,7 +28,7 @@
 .\"     From: @(#)swapon.8	8.1 (Berkeley) 6/5/93
 .\" $FreeBSD$
 .\"
-.Dd May 12, 1995
+.Dd April 29, 2013
 .Dt DUMPON 8
 .Os
 .Sh NAME
@@ -59,14 +59,21 @@ controlled by the
 variable in the boot time configuration file
 .Pa /etc/rc.conf .
 .Pp
-For most systems the size of the specified dump device must be at
+The default type of kernel crash dump is the mini crash dump.
+Mini crash dumps hold only memory pages in use by the kernel.
+Alternatively, full memory dumps can be enabled by setting the
+.Va debug.minidump
+.Xr sysctl 8
+variable to 0.
+.Pp
+For systems using full memory dumps, the size of the specified dump
+device must be at
 least the size of physical memory.
 Even though an additional 64 kB header is added to the dump, the BIOS for a
 platform typically holds back some memory, so it is not usually
 necessary to size the dump device larger than the actual amount of RAM
 available in the machine.
-.Pp
-The
+Also, when using full memory dumps, the
 .Nm
 utility will refuse to enable a dump device which is smaller than the
 total amount of physical memory as reported by the
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Comment 4 Tommy Wilkinson 2022-12-07 14:56:35 UTC

After updating the man page, I'll close this PR. https://flappy-bird.co