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28 .\" From: @(#)swapon.8 8.1 (Berkeley) 6/5/93
36 .Nd "specify a device for crash dumps"
50 utility is used to specify a device where the kernel can save a crash
51 dump in the case of a panic.
55 normally occur from the system multi-user initialization file
59 variable in the boot time configuration file
62 The default type of kernel crash dump is the mini crash dump.
63 Mini crash dumps hold only memory pages in use by the kernel.
64 Alternatively, full memory dumps can be enabled by setting the
69 For systems using full memory dumps, the size of the specified dump
71 least the size of physical memory.
72 Even though an additional 64 kB header is added to the dump, the BIOS for a
73 platform typically holds back some memory, so it is not usually
74 necessary to size the dump device larger than the actual amount of RAM
75 available in the machine.
76 Also, when using full memory dumps, the
78 utility will refuse to enable a dump device which is smaller than the
79 total amount of physical memory as reported by the
88 to print the current dump device or _PATH_DEVNULL ("/dev/null") if no device is
95 to be verbose about its activity.
96 .Sh IMPLEMENTATION NOTES
99 condition may occur in a situation
100 where the kernel cannot trust its internal representation
101 of the state of any given file system,
102 one of the system swap devices,
105 a device containing a file system,
106 should be used as the dump device.
110 utility operates by opening
115 request on it to save kernel crash dumps.
126 and thus instructs the kernel not to save crash dumps.
130 cannot be used during kernel initialization, the
134 must be used to enable dumps for system panics which occur
135 during kernel initialization.
137 .Bl -tag -width "/dev/{ada,da}?s?b" -compact
138 .It Pa /dev/{ada,da}?s?b
141 boot-time system configuration
159 Because the file system layer is already dead by the time a crash dump
160 is taken, it is not possible to send crash dumps directly to a file.