1REBOOT(2) Linux Programmer's Manual REBOOT(2)
2
6 reboot - reboot or enable/disable Ctrl-Alt-Del
7
9 /* Since kernel version 2.1.30 there are symbolic names LINUX_REBOOT_*
10 for the constants and a fourth argument to the call: */
11 #include <linux/reboot.h> /* Definition of LINUX_REBOOT_* constants */
13 #include <sys/syscall.h> /* Definition of SYS_* constants */
14 #include <unistd.h>
15 int syscall(SYS_reboot, int magic, int magic2, int cmd, void *arg);
17 /* Under glibc and most alternative libc's (including uclibc, dietlibc,
19 musl and a few others), some of the constants involved have gotten
20 symbolic names RB_*, and the library call is a 1-argument
21 wrapper around the system call: */
22 #include <sys/reboot.h> /* Definition of RB_* constants */
24 #include <unistd.h>
25 int reboot(int cmd);
27
29 The reboot() call reboots the system, or enables/disables the reboot
30 keystroke (abbreviated CAD, since the default is Ctrl-Alt-Delete; it
31 can be changed using loadkeys(1)).
32 This system call fails (with the error EINVAL) unless magic equals
34 LINUX_REBOOT_MAGIC1 (that is, 0xfee1dead) and magic2 equals LINUX_RE‐
35 BOOT_MAGIC2 (that is, 672274793). However, since 2.1.17 also LINUX_RE‐
36 BOOT_MAGIC2A (that is, 85072278) and since 2.1.97 also LINUX_RE‐
37 BOOT_MAGIC2B (that is, 369367448) and since 2.5.71 also LINUX_RE‐
38 BOOT_MAGIC2C (that is, 537993216) are permitted as values for magic2.
39 (The hexadecimal values of these constants are meaningful.)
40 The cmd argument can have the following values:
42 LINUX_REBOOT_CMD_CAD_OFF
44 (RB_DISABLE_CAD, 0). CAD is disabled. This means that the CAD
45 keystroke will cause a SIGINT signal to be sent to init (process
46 1), whereupon this process may decide upon a proper action
47 (maybe: kill all processes, sync, reboot).
48 LINUX_REBOOT_CMD_CAD_ON
50 (RB_ENABLE_CAD, 0x89abcdef). CAD is enabled. This means that
51 the CAD keystroke will immediately cause the action associated
52 with LINUX_REBOOT_CMD_RESTART.
53 LINUX_REBOOT_CMD_HALT
55 (RB_HALT_SYSTEM, 0xcdef0123; since Linux 1.1.76). The message
56 "System halted." is printed, and the system is halted. Control
57 is given to the ROM monitor, if there is one. If not preceded
58 by a sync(2), data will be lost.
59 LINUX_REBOOT_CMD_KEXEC
61 (RB_KEXEC, 0x45584543, since Linux 2.6.13). Execute a kernel
62 that has been loaded earlier with kexec_load(2). This option is
63 available only if the kernel was configured with CONFIG_KEXEC.
64 LINUX_REBOOT_CMD_POWER_OFF
66 (RB_POWER_OFF, 0x4321fedc; since Linux 2.1.30). The message
67 "Power down." is printed, the system is stopped, and all power
68 is removed from the system, if possible. If not preceded by a
69 sync(2), data will be lost.
70 LINUX_REBOOT_CMD_RESTART
72 (RB_AUTOBOOT, 0x1234567). The message "Restarting system." is
73 printed, and a default restart is performed immediately. If not
74 preceded by a sync(2), data will be lost.
75 LINUX_REBOOT_CMD_RESTART2
77 (0xa1b2c3d4; since Linux 2.1.30). The message "Restarting sys‐
78 tem with command '%s'" is printed, and a restart (using the com‐
79 mand string given in arg) is performed immediately. If not pre‐
80 ceded by a sync(2), data will be lost.
81 LINUX_REBOOT_CMD_SW_SUSPEND
83 (RB_SW_SUSPEND, 0xd000fce1; since Linux 2.5.18). The system is
84 suspended (hibernated) to disk. This option is available only
85 if the kernel was configured with CONFIG_HIBERNATION.
86 Only the superuser may call reboot().
88 The precise effect of the above actions depends on the architecture.
90 For the i386 architecture, the additional argument does not do anything
91 at present (2.1.122), but the type of reboot can be determined by ker‐
92 nel command-line arguments ("reboot=...") to be either warm or cold,
93 and either hard or through the BIOS.
94 Behavior inside PID namespaces
96 Since Linux 3.4, if reboot() is called from a PID namespace other than
97 the initial PID namespace with one of the cmd values listed below, it
98 performs a "reboot" of that namespace: the "init" process of the PID
99 namespace is immediately terminated, with the effects described in
100 pid_namespaces(7).
101 The values that can be supplied in cmd when calling reboot() in this
103 case are as follows:
104 LINUX_REBOOT_CMD_RESTART, LINUX_REBOOT_CMD_RESTART2
106 The "init" process is terminated, and wait(2) in the parent
107 process reports that the child was killed with a SIGHUP signal.
108 LINUX_REBOOT_CMD_POWER_OFF, LINUX_REBOOT_CMD_HALT
110 The "init" process is terminated, and wait(2) in the parent
111 process reports that the child was killed with a SIGINT signal.
112 For the other cmd values, reboot() returns -1 and errno is set to EIN‐
114 VAL.
115
117 For the values of cmd that stop or restart the system, a successful
118 call to reboot() does not return. For the other cmd values, zero is
119 returned on success. In all cases, -1 is returned on failure, and er‐
120 rno is set to indicate the error.
121
123 EFAULT Problem with getting user-space data under LINUX_RE‐
124 BOOT_CMD_RESTART2.
125 EINVAL Bad magic numbers or cmd.
127 EPERM The calling process has insufficient privilege to call reboot();
129 the caller must have the CAP_SYS_BOOT inside its user namespace.
130
132 reboot() is Linux-specific, and should not be used in programs intended
133 to be portable.
134
136 systemctl(1), systemd(1), kexec_load(2), sync(2), bootparam(7), capa‐
137 bilities(7), ctrlaltdel(8), halt(8), shutdown(8)
138
140 This page is part of release 5.13 of the Linux man-pages project. A
141 description of the project, information about reporting bugs, and the
142 latest version of this page, can be found at
143 https://www.kernel.org/doc/man-pages/.
144Linux 2021-03-22 REBOOT(2)