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28 .\" From: @(#)swapon.8 8.1 (Berkeley) 6/5/93
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31 .Dd September 23, 2018
36 .Nd "specify a device for crash dumps"
46 utility is used to specify a device where the kernel can save a crash dump in
51 normally occur from the system multi-user initialization file
55 variable in the boot time configuration file
58 The default type of kernel crash dump is the mini crash dump.
59 Mini crash dumps hold only memory pages in use by the kernel.
60 Alternatively, full memory dumps can be enabled by setting the
65 For most systems the size of the specified dump device must be at least
66 the size of physical memory.
67 Even though an additional header is added to the dump,
68 the BIOS for a platform typically holds back some memory, so it is not usually
69 necessary to size the dump device larger than the actual amount of RAM
70 available in the machine.
74 condition may occur in a situation
75 where the kernel cannot trust its internal representation
76 of the state of any given file system,
77 one of the system swap devices,
80 a device containing a file system,
81 should be used as the dump device.
85 utility operates by setting the
89 to the device number of the designated
93 (meaning that no dumps are to be taken) if the utility is invoked as
100 In order to change the device for crash dumps, one needs to run the
102 utility to disable the current dump device before configuring the new one.
106 cannot be used during kernel initialization, the
110 must be used to enable dumps for system panics which occur
111 during kernel initialization.
113 .Bl -tag -width "/dev/{ad,da}?s?b" -compact
114 .It Pa /dev/{ad,da}?s?b
117 boot-time system configuration
136 utility first appeared in
139 Because the file system layer is already dead by the time a crash dump
140 is taken, it is not possible to send crash dumps directly to a file.