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28 .\" From: @(#)swapon.8 8.1 (Berkeley) 6/5/93
36 .Nd "specify a device for crash dumps"
49 .Op Fl g Ar gateway | Li default
62 utility is used to specify a device where the kernel can save a crash
63 dump in the case of a panic.
67 normally occur from the system multi-user initialization file
73 variables in the boot time configuration file
76 The default type of kernel crash dump is the mini crash dump.
77 Mini crash dumps hold only memory pages in use by the kernel.
78 Alternatively, full memory dumps can be enabled by setting the
83 For systems using full memory dumps, the size of the specified dump
84 device must be at least the size of physical memory.
85 Even though an additional 64 kB header is added to the dump, the BIOS for a
86 platform typically holds back some memory, so it is not usually
87 necessary to size the dump device larger than the actual amount of RAM
88 available in the machine.
89 Also, when using full memory dumps, the
91 utility will refuse to enable a dump device which is smaller than the
92 total amount of physical memory as reported by the
98 is used to configure a local storage device as the dump device.
99 With additional parameters, the kernel can instead be configured to
100 transmit a dump to a remote server using
102 This eliminates the need to reserve space for saving crash dumps and
103 is especially useful in diskless environments.
106 server address is specified with
108 and the local address is specified with
112 parameter may be used to specify a first-hop router to the server,
113 or to specify that the currently configured default gateway is to
117 configuration is not automatically updated if any network configuration
118 (e.g., the default route) changes after the
121 The name of the interface to be used must be specified as
123 The interface must be up in order to configure
130 to generate a one-time key for kernel crash dump encryption.
131 The key will be replaced by a new one when the
133 utility is run again.
134 The key is encrypted using
136 This process is sandboxed using
138 Both plain and encrypted keys are sent to the kernel using
141 A user can specify the
151 This flag requires a kernel compiled with the
159 options configure the kernel to compress the dump before writing it to
161 This reduces the amount of space required for the dump and accelerates
164 since less data needs to be copied from the dump device.
165 When compression is enabled, the
167 utility will not verify that the dump device is sufficiently large for a full
173 options cause the dump to be written in
177 format, respectively.
178 These flags require a kernel compiled with the
188 to print the current dump device or _PATH_DEVNULL ("/dev/null") if no device is
195 to be verbose about its activity.
196 .Sh IMPLEMENTATION NOTES
199 condition may occur in a situation
200 where the kernel cannot trust its internal representation
201 of the state of any given file system,
202 one of the system swap devices,
205 a device containing a file system,
206 should be used as the dump device.
210 utility operates by opening
215 request on it to save kernel crash dumps.
226 and thus instructs the kernel not to save crash dumps.
230 cannot be used during kernel initialization, the
234 must be used to enable dumps for system panics which occur
235 during kernel initialization.
237 .Bl -tag -width "/dev/{ada,da}?s?b" -compact
238 .It Pa /dev/{ada,da}?s?b
241 boot-time system configuration
244 In order to generate an RSA private key a user can use the
248 .Dl # openssl genrsa -out private.pem 4096
250 A public key can be extracted from the private key using the
254 .Dl # openssl rsa -in private.pem -out public.pem -pubout
256 Once the RSA keys are created the private key should be moved to a safe place.
261 to configure encrypted kernel crash dumps:
263 .Dl # dumpon -k public.pem /dev/ada0s1b
265 It is recommended to test if the kernel saves encrypted crash dumps using the
266 current configuration.
267 The easiest way to do that is to cause a kernel panic using the
271 .Dl # sysctl debug.kdb.panic=1
273 In the debugger the following commands should be typed to write a core dump and
276 .Dl db> call doadump(0)
281 should be able to save the core dump in the core directory which is
285 .Dl # savecore /var/crash /dev/ada0s1b
287 Three files should be created in the core directory:
291 .Pa vmcore_encrypted.#
294 is the number of the last core dump saved by
297 .Pa vmcore_encrypted.#
298 can be decrypted using the
302 .Dl # decryptcore -p private.pem -k key.# -e vmcore_encrypted.# -c vmcore.#
306 .Dl # decryptcore -p private.pem -n #
310 can be now examined using
313 .Dl # kgdb /boot/kernel/kernel vmcore.#
319 The core was decrypted properly if
321 does not print any errors.
322 Note that the live kernel might be at a different path
323 which can be examined by looking at the kern.bootfile sysctl.
345 Because the file system layer is already dead by the time a crash dump
346 is taken, it is not possible to send crash dumps directly to a file.
348 It is currently not possible to configure both compression and encryption.
349 The encrypted dump format assumes that the kernel dump size is a multiple
350 of the cipher block size, which may not be true when the dump is compressed.