dumpon(8): Add "dumpoff" variant to be "dumpon off"
[dragonfly.git] / sbin / dumpon / dumpon.8
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28.\" From: @(#)swapon.8 8.1 (Berkeley) 6/5/93
29.\" $FreeBSD: src/sbin/dumpon/dumpon.8,v 1.11.2.12 2003/01/26 03:12:04 keramida Exp $
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03f2fdd2 31.Dd September 22, 2018
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32.Dt DUMPON 8
33.Os
34.Sh NAME
03f2fdd2 35.Nm dumpon , dumpoff
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36.Nd "specify a device for crash dumps"
37.Sh SYNOPSIS
38.Nm
39.Op Fl v
40.Ar special_file
41.Nm
42.Op Fl v
c83d7bab 43.Cm off
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44.Nm dumpoff
45.Op Fl v
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46.Sh DESCRIPTION
47The
48.Nm
49utility is used to specify a device where the kernel can save a crash dump in
50the case of a panic.
51.Pp
52Calls to
53.Nm
54normally occur from the system multi-user initialization file
55.Pa /etc/rc ,
56controlled by the
57.Dq dumpdev
58variable in the boot time configuration file
59.Pa /etc/rc.conf .
60.Pp
61For most systems the size of the specified dump device must be at least
62the size of physical memory.
63Even though an additional header is added to the dump,
64the BIOS for a platform typically holds back some memory, so it is not usually
65necessary to size the dump device larger than the actual amount of RAM
66available in the machine.
67.Pp
68The
69.Fl v
70flag causes
71.Nm
72to be verbose about its activity.
73.Sh NOTES
74Since a
75.Xr panic 9
76condition may occur in a situation
77where the kernel cannot trust its internal representation
78of the state of any given file system,
79one of the system swap devices,
80and
81.Em not
82a device containing a file system,
83should be used as the dump device.
84.Pp
85The
86.Nm
87utility operates by setting the
88.Xr sysctl 3
89MIB variable
e9c76aaf 90.Va kern.dumpdev
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91to the device number of the designated
92.Ar special_file
93or to
94.Dv NODEV
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95(meaning that no dumps are to be taken) if the utility is invoked as
96.Nm dumpoff
97or if
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98.Ar special_file
99is the text string:
100.Dq Li off .
101.Pp
102Since
103.Nm
104cannot be used during kernel initialization, the
105.Va dumpdev
106variable of
107.Xr loader 8
108must be used to enable dumps for system panics which occur
109during kernel initialization.
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110.Sh FILES
111.Bl -tag -width "/dev/{ad,da}?s?b" -compact
112.It Pa /dev/{ad,da}?s?b
113standard swap areas
114.It Pa /etc/rc.conf
115boot-time system configuration
116.El
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117.Sh SEE ALSO
118.Xr sysctl 3 ,
119.Xr fstab 5 ,
120.Xr rc.conf 5 ,
121.Xr config 8 ,
122.Xr init 8 ,
123.Xr loader 8 ,
124.Xr rc 8 ,
125.Xr savecore 8 ,
126.Xr swapon 8 ,
127.Xr panic 9
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128.Sh HISTORY
129The
130.Nm
131utility appeared in
0b674f74 132.Fx 2.0.5 .
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133The
134.Nm dumpoff
135utility first appeared in
136.Dx 5.3 .
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137.Sh BUGS
138Because the file system layer is already dead by the time a crash dump
139is taken, it is not possible to send crash dumps directly to a file.