xref: /freebsd/sbin/dumpon/dumpon.8 (revision a220d00e74dd245b4fca59c5eca0c53963686325)
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32.\"     From: @(#)swapon.8	8.1 (Berkeley) 6/5/93
33.\" $FreeBSD$
34.\"
35.Dd May 12, 1995
36.Dt DUMPON 8
37.Os
38.Sh NAME
39.Nm dumpon
40.Nd "specify a device for crash dumps"
41.Sh SYNOPSIS
42.Nm
43.Op Fl v
44.Ar special_file
45.Nm
46.Op Fl v
47.Ar off
48.Sh DESCRIPTION
49.Nm Dumpon
50is used to specify a device where the kernel can save a crash dump in
51the case of a panic.
52.Pp
53Calls to
54.Nm
55normally occur from the system multi-user initialization file
56.Pa /etc/rc ,
57controlled by the
58.Dq dumpdev
59variable in the boot time configuration file
60.Pa /etc/rc.conf .
61.Pp
62The size of the specified dump device must be at least 64 KB greater
63than the size of physical memory.
64.Pp
65The
66.Fl v
67flag causes
68.Nm
69to be verbose about its activity.
70.Sh NOTES
71Since a
72.Xr panic 9
73condition may occur in a situation
74where the kernel cannot trust its internal representation
75of the state of any given filesystem,
76one of the system swap devices,
77and
78.Em not
79a device containing a filesystem,
80should be used as the dump device.
81.Pp
82The
83.Nm
84program operates by setting the
85.Xr sysctl 3
86MIB variable
87.Dq kern.dumpdev
88to the device number of the designated
89.Ar special_file
90or to
91.Dv NODEV
92(meaning that no dumps are to be taken) if
93.Ar special_file
94is the text string:
95.Dq Li off .
96.Sh SEE ALSO
97.Xr sysctl 3 ,
98.Xr fstab 5 ,
99.Xr rc.conf 5 ,
100.Xr config 8 ,
101.Xr init 8 ,
102.Xr rc 8 ,
103.Xr savecore 8 ,
104.Xr swapon 8 ,
105.Xr panic 9
106.Sh FILES
107.Bl -tag -width "/dev/{ad,da}?s?b" -compact
108.It Pa /dev/{ad,da}?s?b
109standard swap areas
110.It Pa /etc/rc.conf
111boot-time system configuration
112.El
113.Sh BUGS
114Because the filesystem layer is already dead by the time a crash dump
115is taken, it is not possible to send crash dumps directly to a file.
116.Pp
117Since
118.Nm
119can only be called after the system enters single-user mode,
120it can not be used to create dumps
121for system panics during kernel initialization.
122.Sh HISTORY
123The
124.Nm
125command appeared in
126.Fx 2.1 .
127