1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" From: @(#)swapon.8 8.1 (Berkeley) 6/5/93 29.\" $FreeBSD$ 30.\" 31.Dd June 13, 2018 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.Op Fl k Ar pubkey 41.Op Fl Z 42.Op Fl z 43.Ar device 44.Nm 45.Op Fl v 46.Op Fl k Ar pubkey 47.Op Fl Z 48.Op Fl z 49.Op Fl g Ar gateway | Li default 50.Fl s Ar server 51.Fl c Ar client 52.Ar iface 53.Nm 54.Op Fl v 55.Cm off 56.Nm 57.Op Fl v 58.Fl l 59.Sh DESCRIPTION 60The 61.Nm 62utility is used to specify a device where the kernel can save a crash 63dump in the case of a panic. 64.Pp 65Calls to 66.Nm 67normally occur from the system multi-user initialization file 68.Pa /etc/rc , 69controlled by the 70.Dq dumpdev 71and 72.Dq dumpon_flags 73variables in the boot time configuration file 74.Pa /etc/rc.conf . 75.Pp 76The default type of kernel crash dump is the mini crash dump. 77Mini crash dumps hold only memory pages in use by the kernel. 78Alternatively, full memory dumps can be enabled by setting the 79.Va debug.minidump 80.Xr sysctl 8 81variable to 0. 82.Pp 83For systems using full memory dumps, the size of the specified dump 84device must be at least the size of physical memory. 85Even though an additional 64 kB header is added to the dump, the BIOS for a 86platform typically holds back some memory, so it is not usually 87necessary to size the dump device larger than the actual amount of RAM 88available in the machine. 89Also, when using full memory dumps, the 90.Nm 91utility will refuse to enable a dump device which is smaller than the 92total amount of physical memory as reported by the 93.Va hw.physmem 94.Xr sysctl 8 95variable. 96.Pp 97.Nm 98is used to configure a local storage device as the dump device. 99With additional parameters, the kernel can instead be configured to 100transmit a dump to a remote server using 101.Xr netdump 4 . 102This eliminates the need to reserve space for saving crash dumps and 103is especially useful in diskless environments. 104The 105.Xr netdump 4 106server address is specified with 107.Fl s Ar server , 108and the local address is specified with 109.Fl c Ar client . 110The 111.Fl g Ar gateway 112parameter may be used to specify a first-hop router to the server, 113or to specify that the currently configured default gateway is to 114be used. 115Note that the 116.Xr netdump 4 117configuration is not automatically updated if any network configuration 118(e.g., the default route) changes after the 119.Nm 120invocation. 121The name of the interface to be used must be specified as 122.Ar iface . 123The interface must be up in order to configure 124.Xr netdump 4 . 125.Pp 126The 127.Fl k Ar pubkey 128flag causes 129.Nm 130to generate a one-time key for kernel crash dump encryption. 131The key will be replaced by a new one when the 132.Nm 133utility is run again. 134The key is encrypted using 135.Ar pubkey . 136This process is sandboxed using 137.Xr capsicum 4 . 138Both plain and encrypted keys are sent to the kernel using 139.Dv DIOCSKERNELDUMP 140.Xr ioctl 2 . 141A user can specify the 142.Ar pubkey 143in the 144.Dq dumpon_flags 145variable defined in 146.Pa /etc/rc.conf 147for use with the 148.Pa /etc/rc.d/dumpon 149.Xr rc 8 150script. 151This flag requires a kernel compiled with the 152.Dv EKCD 153kernel option. 154.Pp 155The 156.Fl z 157and 158.Fl Z 159options configure the kernel to compress the dump before writing it to 160the dump device. 161This reduces the amount of space required for the dump and accelerates 162recovery with 163.Xr savecore 8 164since less data needs to be copied from the dump device. 165When compression is enabled, the 166.Nm 167utility will not verify that the dump device is sufficiently large for a full 168dump. 169The 170.Fl z 171and 172.Fl Z 173options cause the dump to be written in 174.Xr gzip 1 175and 176.Xr zstd 1 177format, respectively. 178These flags require a kernel compiled with the 179.Dv GZIO 180or 181.Dv ZSTDIO 182kernel options. 183.Pp 184The 185.Fl l 186flag causes 187.Nm 188to print the current dump device or _PATH_DEVNULL ("/dev/null") if no device is 189configured. 190.Pp 191The 192.Fl v 193flag causes 194.Nm 195to be verbose about its activity. 196.Sh IMPLEMENTATION NOTES 197Since a 198.Xr panic 9 199condition may occur in a situation 200where the kernel cannot trust its internal representation 201of the state of any given file system, 202one of the system swap devices, 203and 204.Em not 205a device containing a file system, 206should be used as the dump device. 207.Pp 208The 209.Nm 210utility operates by opening 211.Ar device 212and making a 213.Dv DIOCSKERNELDUMP 214.Xr ioctl 2 215request on it to save kernel crash dumps. 216If 217.Ar device 218is the text string: 219.Dq Li off , 220.Nm 221performs a 222.Dv DIOCSKERNELDUMP 223.Xr ioctl 2 224on 225.Pa /dev/null 226and thus instructs the kernel not to save crash dumps. 227.Pp 228Since 229.Nm 230cannot be used during kernel initialization, the 231.Va dumpdev 232variable of 233.Xr loader 8 234must be used to enable dumps for system panics which occur 235during kernel initialization. 236.Sh FILES 237.Bl -tag -width "/dev/{ada,da}?s?b" -compact 238.It Pa /dev/{ada,da}?s?b 239standard swap areas 240.It Pa /etc/rc.conf 241boot-time system configuration 242.El 243.Sh EXAMPLES 244In order to generate an RSA private key a user can use the 245.Xr genrsa 1 246tool: 247.Pp 248.Dl # openssl genrsa -out private.pem 4096 249.Pp 250A public key can be extracted from the private key using the 251.Xr rsa 1 252tool: 253.Pp 254.Dl # openssl rsa -in private.pem -out public.pem -pubout 255.Pp 256Once the RSA keys are created the private key should be moved to a safe place. 257Now 258.Pa public.pem 259can be used by 260.Nm 261to configure encrypted kernel crash dumps: 262.Pp 263.Dl # dumpon -k public.pem /dev/ada0s1b 264.Pp 265It is recommended to test if the kernel saves encrypted crash dumps using the 266current configuration. 267The easiest way to do that is to cause a kernel panic using the 268.Xr ddb 4 269debugger: 270.Pp 271.Dl # sysctl debug.kdb.panic=1 272.Pp 273In the debugger the following commands should be typed to write a core dump and 274reboot: 275.Pp 276.Dl db> call doadump(0) 277.Dl db> reset 278.Pp 279After reboot 280.Xr savecore 8 281should be able to save the core dump in the core directory which is 282.Pa /var/crash 283by default: 284.Pp 285.Dl # savecore /var/crash /dev/ada0s1b 286.Pp 287Three files should be created in the core directory: 288.Pa info.# , 289.Pa key.# 290and 291.Pa vmcore_encrypted.# 292where 293.Dq # 294is the number of the last core dump saved by 295.Xr savecore 8 . 296The 297.Pa vmcore_encrypted.# 298can be decrypted using the 299.Xr decryptcore 8 300utility: 301.Pp 302.Dl # decryptcore -p private.pem -k key.# -e vmcore_encrypted.# -c vmcore.# 303.Pp 304or shorter: 305.Pp 306.Dl # decryptcore -p private.pem -n # 307.Pp 308The 309.Pa vmcore.# 310can be now examined using 311.Xr kgdb 1 : 312.Pp 313.Dl # kgdb /boot/kernel/kernel vmcore.# 314.Pp 315or shorter: 316.Pp 317.Dl # kgdb -n # 318.Pp 319The core was decrypted properly if 320.Xr kgdb 1 321does not print any errors. 322Note that the live kernel might be at a different path 323which can be examined by looking at the kern.bootfile sysctl. 324.Sh SEE ALSO 325.Xr gzip 1 , 326.Xr kgdb 1 , 327.Xr zstd 1 , 328.Xr ddb 4 , 329.Xr fstab 5 , 330.Xr rc.conf 5 , 331.Xr config 8 , 332.Xr decryptcore 8 , 333.Xr init 8 , 334.Xr loader 8 , 335.Xr rc 8 , 336.Xr savecore 8 , 337.Xr swapon 8 , 338.Xr panic 9 339.Sh HISTORY 340The 341.Nm 342utility appeared in 343.Fx 2.0.5 . 344.Sh BUGS 345Because the file system layer is already dead by the time a crash dump 346is taken, it is not possible to send crash dumps directly to a file. 347.Pp 348It is currently not possible to configure both compression and encryption. 349The encrypted dump format assumes that the kernel dump size is a multiple 350of the cipher block size, which may not be true when the dump is compressed. 351