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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.\" @(#)reboot.2 8.1 (Berkeley) 6/4/93 29.\" 30.Dd July 10, 2018 31.Dt REBOOT 2 32.Os 33.Sh NAME 34.Nm reboot 35.Nd reboot system or halt processor 36.Sh LIBRARY 37.Lb libc 38.Sh SYNOPSIS 39.In unistd.h 40.In sys/reboot.h 41.Ft int 42.Fn reboot "int howto" 43.Sh DESCRIPTION 44The 45.Fn reboot 46system call 47reboots the system. 48Only the super-user may reboot a machine on demand. 49However, a reboot is invoked 50automatically in the event of unrecoverable system failures. 51.Pp 52The 53.Fa howto 54argument 55is a mask of options; the system call interface allows the following 56options, defined in the include file 57.In sys/reboot.h , 58to be passed 59to the new kernel or the new bootstrap and init programs. 60.Bl -tag -width RB_POWERCYCLE 61.It Dv RB_AUTOBOOT 62The default, causing the system to reboot in its usual fashion. 63.It Dv RB_ASKNAME 64Normally the system only prompts the user if the loader specified root 65file system has an error. 66This flag forces it to always prompt the user for the root partition. 67.It Dv RB_DFLTROOT 68Use the compiled in root device. 69Normally, the system uses the device from which it was booted 70as the root device if possible. 71(The default behavior is dependent on the ability of the bootstrap program 72to determine the drive from which it was loaded, which is not possible 73on all systems.) 74.It Dv RB_DUMP 75Dump kernel memory before rebooting; see 76.Xr savecore 8 77for more information. 78.It Dv RB_HALT 79The processor is simply halted; no reboot takes place. 80This option should be used with caution. 81.It Dv RB_POWERCYCLE 82After halting, the shutdown code will do what it can to turn 83off the power and then turn the power back on. 84This requires hardware support, usually an auxiliary microprocessor 85that can sequence the power supply. 86At present only the 87.Xr ipmi 4 88driver implements this feature. 89.It Dv RB_POWEROFF 90After halting, the shutdown code will do what it can to turn 91off the power. 92This requires hardware support. 93.It Dv RB_KDB 94Load the symbol table and enable a built-in debugger in the system. 95This option will have no useful function if the kernel is not configured 96for debugging. 97Several other options have different meaning if combined 98with this option, although their use may not be possible 99via the 100.Fn reboot 101system call. 102See 103.Xr ddb 4 104for more information. 105.It Dv RB_NOSYNC 106Normally, the disks are sync'd (see 107.Xr sync 8 ) 108before the processor is halted or rebooted. 109This option may be useful if file system changes have been made manually 110or if the processor is on fire. 111.It Dv RB_REROOT 112Instead of rebooting, unmount all filesystems except the one containing 113currently-running executable, and mount root filesystem using the same 114mechanism which is used during normal boot, based on 115vfs.root.mountfrom 116.Xr kenv 1 117variable. 118.It Dv RB_RDONLY 119Initially mount the root file system read-only. 120This is currently the default, and this option has been deprecated. 121.It Dv RB_SINGLE 122Normally, the reboot procedure involves an automatic disk consistency 123check and then multi-user operations. 124.Dv RB_SINGLE 125prevents this, booting the system with a single-user shell 126on the console. 127.Dv RB_SINGLE 128is actually interpreted by the 129.Xr init 8 130program in the newly booted system. 131.El 132.Pp 133When no options are given (i.e., 134.Dv RB_AUTOBOOT 135is used), the system is 136rebooted from file 137.Dq kernel 138in the root file system of unit 0 139of a disk chosen in a processor specific way. 140An automatic consistency check of the disks is normally performed 141(see 142.Xr fsck 8 ) . 143.Sh RETURN VALUES 144If successful, this call never returns. 145Otherwise, a -1 is returned and an error is returned in the global 146variable 147.Va errno . 148.Sh ERRORS 149.Bl -tag -width Er 150.It Bq Er EPERM 151The caller is not the super-user. 152.El 153.Sh SEE ALSO 154.Xr crash 8 , 155.Xr halt 8 , 156.Xr init 8 , 157.Xr reboot 8 , 158.Xr savecore 8 , 159.Xr reboot 9 160.Sh HISTORY 161The 162.Fn reboot 163system call appeared in 164.Bx 4.0 . 165