xref: /freebsd/sbin/dumpon/dumpon.8 (revision 74bf4e164ba5851606a27d4feff27717452583e5)
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28.\"     From: @(#)swapon.8	8.1 (Berkeley) 6/5/93
29.\" $FreeBSD$
30.\"
31.Dd May 12, 1995
32.Dt DUMPON 8
33.Os
34.Sh NAME
35.Nm dumpon
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
43.Cm off
44.Sh DESCRIPTION
45The
46.Nm
47utility is used to specify a device where the kernel can save a crash dump in
48the case of a panic.
49.Pp
50Calls to
51.Nm
52normally occur from the system multi-user initialization file
53.Pa /etc/rc ,
54controlled by the
55.Dq dumpdev
56variable in the boot time configuration file
57.Pa /etc/rc.conf .
58.Pp
59For most systems the size of the specified dump device must be at least
60the size of physical memory.
61Even though an additional header is added to the dump,
62the BIOS for a platform typically holds back some memory, so it is not usually
63necessary to size the dump device larger than the actual amount of RAM
64available in the machine.
65.Pp
66The
67.Fl v
68flag causes
69.Nm
70to be verbose about its activity.
71.Sh IMPLEMENTATION NOTES
72Since a
73.Xr panic 9
74condition may occur in a situation
75where the kernel cannot trust its internal representation
76of the state of any given file system,
77one of the system swap devices,
78and
79.Em not
80a device containing a file system,
81should be used as the dump device.
82.Pp
83The
84.Nm
85utility operates by opening
86.Ar special_file
87and making a
88.Dv DIOCSKERNELDUMP
89.Xr ioctl 2
90request on it to save kernel crash dumps.
91If
92.Ar special_file
93is the text string:
94.Dq Li off ,
95.Nm
96performs a
97.Dv DIOCSKERNELDUMP
98.Xr ioctl 2
99on
100.Pa /dev/null
101and thus instructs the kernel not to save crash dumps.
102.Pp
103Since
104.Nm
105cannot be used during kernel initialization, the
106.Va dumpdev
107variable of
108.Xr loader 8
109must be used to enable dumps for system panics which occur
110during kernel initialization.
111.Sh SEE ALSO
112.Xr fstab 5 ,
113.Xr rc.conf 5 ,
114.Xr config 8 ,
115.Xr init 8 ,
116.Xr loader 8 ,
117.Xr rc 8 ,
118.Xr savecore 8 ,
119.Xr swapon 8 ,
120.Xr panic 9
121.Sh FILES
122.Bl -tag -width "/dev/{ad,da}?s?b" -compact
123.It Pa /dev/{ad,da}?s?b
124standard swap areas
125.It Pa /etc/rc.conf
126boot-time system configuration
127.El
128.Sh BUGS
129Because the file system layer is already dead by the time a crash dump
130is taken, it is not possible to send crash dumps directly to a file.
131.Sh HISTORY
132The
133.Nm
134utility appeared in
135.Fx 2.1 .
136