| .\" Copyright (c) 1998 Andries Brouwer (aeb@cwi.nl), 24 September 1998 |
| .\" |
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| .\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com> |
| .\" Added notes on capability requirements |
| .\" |
| .TH REBOOT 2 2021-03-22 "Linux" "Linux Programmer's Manual" |
| .SH NAME |
| reboot \- reboot or enable/disable Ctrl-Alt-Del |
| .SH SYNOPSIS |
| .nf |
| /* Since kernel version 2.1.30 there are symbolic names LINUX_REBOOT_* |
| for the constants and a fourth argument to the call: */ |
| .PP |
| .B #include <unistd.h> |
| .B #include <linux/reboot.h> |
| .PP |
| .BI "int reboot(int " magic ", int " magic2 ", int " cmd ", void *" arg ); |
| .PP |
| /* Under glibc and most alternative libc's (including uclibc, dietlibc, |
| musl and a few others), some of the constants involved have gotten |
| symbolic names RB_*, and the library call is a 1-argument |
| wrapper around the system call: */ |
| .PP |
| .B #include <unistd.h> |
| .B #include <sys/reboot.h> |
| .PP |
| .BI "int reboot(int " cmd ); |
| .fi |
| .SH DESCRIPTION |
| The |
| .BR reboot () |
| call reboots the system, or enables/disables the reboot keystroke |
| (abbreviated CAD, since the default is Ctrl-Alt-Delete; |
| it can be changed using |
| .BR loadkeys (1)). |
| .PP |
| This system call fails (with the error |
| .BR EINVAL ) |
| unless |
| .I magic |
| equals |
| .B LINUX_REBOOT_MAGIC1 |
| (that is, 0xfee1dead) and |
| .I magic2 |
| equals |
| .B LINUX_REBOOT_MAGIC2 |
| (that is, 672274793). |
| However, since 2.1.17 also |
| .B LINUX_REBOOT_MAGIC2A |
| (that is, 85072278) |
| and since 2.1.97 also |
| .B LINUX_REBOOT_MAGIC2B |
| (that is, 369367448) |
| and since 2.5.71 also |
| .B LINUX_REBOOT_MAGIC2C |
| (that is, 537993216) |
| are permitted as values for |
| .IR magic2 . |
| (The hexadecimal values of these constants are meaningful.) |
| .PP |
| The |
| .I cmd |
| argument can have the following values: |
| .TP |
| .B LINUX_REBOOT_CMD_CAD_OFF |
| .RB ( RB_DISABLE_CAD , |
| 0). |
| CAD is disabled. |
| This means that the CAD keystroke will cause a |
| .B SIGINT |
| signal to be |
| sent to init (process 1), whereupon this process may decide upon a |
| proper action (maybe: kill all processes, sync, reboot). |
| .TP |
| .B LINUX_REBOOT_CMD_CAD_ON |
| .RB ( RB_ENABLE_CAD , |
| 0x89abcdef). |
| CAD is enabled. |
| This means that the CAD keystroke will immediately cause |
| the action associated with |
| .BR LINUX_REBOOT_CMD_RESTART . |
| .TP |
| .B LINUX_REBOOT_CMD_HALT |
| .RB ( RB_HALT_SYSTEM , |
| 0xcdef0123; since Linux 1.1.76). |
| The message "System halted." is printed, and the system is halted. |
| Control is given to the ROM monitor, if there is one. |
| If not preceded by a |
| .BR sync (2), |
| data will be lost. |
| .TP |
| .BR LINUX_REBOOT_CMD_KEXEC |
| .RB ( RB_KEXEC , |
| 0x45584543, since Linux 2.6.13). |
| Execute a kernel that has been loaded earlier with |
| .BR kexec_load (2). |
| This option is available only if the kernel was configured with |
| .BR CONFIG_KEXEC . |
| .TP |
| .B LINUX_REBOOT_CMD_POWER_OFF |
| .RB ( RB_POWER_OFF , |
| 0x4321fedc; since Linux 2.1.30). |
| The message "Power down." is printed, the system is stopped, |
| and all power is removed from the system, if possible. |
| If not preceded by a |
| .BR sync (2), |
| data will be lost. |
| .TP |
| .B LINUX_REBOOT_CMD_RESTART |
| .RB ( RB_AUTOBOOT , |
| 0x1234567). |
| The message "Restarting system." is printed, and a default |
| restart is performed immediately. |
| If not preceded by a |
| .BR sync (2), |
| data will be lost. |
| .TP |
| .B LINUX_REBOOT_CMD_RESTART2 |
| (0xa1b2c3d4; since Linux 2.1.30). |
| The message "Restarting system with command \(aq%s\(aq" is printed, |
| and a restart (using the command string given in |
| .IR arg ) |
| is performed immediately. |
| If not preceded by a |
| .BR sync (2), |
| data will be lost. |
| .TP |
| .BR LINUX_REBOOT_CMD_SW_SUSPEND |
| .RB ( RB_SW_SUSPEND , |
| 0xd000fce1; since Linux 2.5.18). |
| The system is suspended (hibernated) to disk. |
| This option is available only if the kernel was configured with |
| .BR CONFIG_HIBERNATION . |
| .PP |
| Only the superuser may call |
| .BR reboot (). |
| .PP |
| The precise effect of the above actions depends on the architecture. |
| For the i386 architecture, the additional argument does not do |
| anything at present (2.1.122), but the type of reboot can be |
| determined by kernel command-line arguments ("reboot=...") to be |
| either warm or cold, and either hard or through the BIOS. |
| .\" |
| .SS Behavior inside PID namespaces |
| .\" commit cf3f89214ef6a33fad60856bc5ffd7bb2fc4709b |
| .\" see also commit 923c7538236564c46ee80c253a416705321f13e3 |
| Since Linux 3.4, |
| if |
| .BR reboot () |
| is called |
| from a PID namespace other than the initial PID namespace |
| with one of the |
| .I cmd |
| values listed below, |
| it performs a "reboot" of that namespace: |
| the "init" process of the PID namespace is immediately terminated, |
| with the effects described in |
| .BR pid_namespaces (7). |
| .PP |
| The values that can be supplied in |
| .I cmd |
| when calling |
| .BR reboot () |
| in this case are as follows: |
| .TP |
| .BR LINUX_REBOOT_CMD_RESTART ", " LINUX_REBOOT_CMD_RESTART2 |
| The "init" process is terminated, |
| and |
| .BR wait (2) |
| in the parent process reports that the child was killed with a |
| .B SIGHUP |
| signal. |
| .TP |
| .BR LINUX_REBOOT_CMD_POWER_OFF ", " LINUX_REBOOT_CMD_HALT |
| The "init" process is terminated, |
| and |
| .BR wait (2) |
| in the parent process reports that the child was killed with a |
| .B SIGINT |
| signal. |
| .PP |
| For the other |
| .I cmd |
| values, |
| .BR reboot () |
| returns \-1 and |
| .I errno |
| is set to |
| .BR EINVAL . |
| .SH RETURN VALUE |
| For the values of |
| .I cmd |
| that stop or restart the system, |
| a successful call to |
| .BR reboot () |
| does not return. |
| For the other |
| .I cmd |
| values, zero is returned on success. |
| In all cases, \-1 is returned on failure, and |
| .I errno |
| is set to indicate the error. |
| .SH ERRORS |
| .TP |
| .B EFAULT |
| Problem with getting user-space data under |
| .BR LINUX_REBOOT_CMD_RESTART2 . |
| .TP |
| .B EINVAL |
| Bad magic numbers or \fIcmd\fP. |
| .TP |
| .B EPERM |
| The calling process has insufficient privilege to call |
| .BR reboot (); |
| the caller must have the |
| .B CAP_SYS_BOOT |
| inside its user namespace. |
| .SH CONFORMING TO |
| .BR reboot () |
| is Linux-specific, |
| and should not be used in programs intended to be portable. |
| .SH SEE ALSO |
| .BR systemctl (1), |
| .BR systemd (1), |
| .BR kexec_load (2), |
| .BR sync (2), |
| .BR bootparam (7), |
| .BR capabilities (7), |
| .BR ctrlaltdel (8), |
| .BR halt (8), |
| .BR shutdown (8) |