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