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 <unistd.h>
13 #include <linux/reboot.h>
14 int reboot(int magic, int magic2, int cmd, void *arg);
16 /* Under glibc and most alternative libc's (including uclibc, dietlibc,
18 musl and a few others), some of the constants involved have gotten
19 symbolic names RB_*, and the library call is a 1-argument
20 wrapper around the system call: */
21 #include <unistd.h>
23 #include <sys/reboot.h>
24 int reboot(int cmd);
26
28 The reboot() call reboots the system, or enables/disables the reboot
29 keystroke (abbreviated CAD, since the default is Ctrl-Alt-Delete; it
30 can be changed using loadkeys(1)).
31 This system call fails (with the error EINVAL) unless magic equals
33 LINUX_REBOOT_MAGIC1 (that is, 0xfee1dead) and magic2 equals LINUX_RE‐
34 BOOT_MAGIC2 (that is, 672274793). However, since 2.1.17 also LINUX_RE‐
35 BOOT_MAGIC2A (that is, 85072278) and since 2.1.97 also LINUX_RE‐
36 BOOT_MAGIC2B (that is, 369367448) and since 2.5.71 also LINUX_RE‐
37 BOOT_MAGIC2C (that is, 537993216) are permitted as values for magic2.
38 (The hexadecimal values of these constants are meaningful.)
39 The cmd argument can have the following values:
41 LINUX_REBOOT_CMD_CAD_OFF
43 (RB_DISABLE_CAD, 0). CAD is disabled. This means that the CAD
44 keystroke will cause a SIGINT signal to be sent to init (process
45 1), whereupon this process may decide upon a proper action
46 (maybe: kill all processes, sync, reboot).
47 LINUX_REBOOT_CMD_CAD_ON
49 (RB_ENABLE_CAD, 0x89abcdef). CAD is enabled. This means that
50 the CAD keystroke will immediately cause the action associated
51 with LINUX_REBOOT_CMD_RESTART.
52 LINUX_REBOOT_CMD_HALT
54 (RB_HALT_SYSTEM, 0xcdef0123; since Linux 1.1.76). The message
55 "System halted." is printed, and the system is halted. Control
56 is given to the ROM monitor, if there is one. If not preceded
57 by a sync(2), data will be lost.
58 LINUX_REBOOT_CMD_KEXEC
60 (RB_KEXEC, 0x45584543, since Linux 2.6.13). Execute a kernel
61 that has been loaded earlier with kexec_load(2). This option is
62 available only if the kernel was configured with CONFIG_KEXEC.
63 LINUX_REBOOT_CMD_POWER_OFF
65 (RB_POWER_OFF, 0x4321fedc; since Linux 2.1.30). The message
66 "Power down." is printed, the system is stopped, and all power
67 is removed from the system, if possible. If not preceded by a
68 sync(2), data will be lost.
69 LINUX_REBOOT_CMD_RESTART
71 (RB_AUTOBOOT, 0x1234567). The message "Restarting system." is
72 printed, and a default restart is performed immediately. If not
73 preceded by a sync(2), data will be lost.
74 LINUX_REBOOT_CMD_RESTART2
76 (0xa1b2c3d4; since Linux 2.1.30). The message "Restarting sys‐
77 tem with command '%s'" is printed, and a restart (using the com‐
78 mand string given in arg) is performed immediately. If not pre‐
79 ceded by a sync(2), data will be lost.
80 LINUX_REBOOT_CMD_SW_SUSPEND
82 (RB_SW_SUSPEND, 0xd000fce1; since Linux 2.5.18). The system is
83 suspended (hibernated) to disk. This option is available only
84 if the kernel was configured with CONFIG_HIBERNATION.
85 Only the superuser may call reboot().
87 The precise effect of the above actions depends on the architecture.
89 For the i386 architecture, the additional argument does not do anything
90 at present (2.1.122), but the type of reboot can be determined by ker‐
91 nel command-line arguments ("reboot=...") to be either warm or cold,
92 and either hard or through the BIOS.
93 Behavior inside PID namespaces
95 Since Linux 3.4, if reboot() is called from a PID namespace other than
96 the initial PID namespace with one of the cmd values listed below, it
97 performs a "reboot" of that namespace: the "init" process of the PID
98 namespace is immediately terminated, with the effects described in
99 pid_namespaces(7).
100 The values that can be supplied in cmd when calling reboot() in this
102 case are as follows:
103 LINUX_REBOOT_CMD_RESTART, LINUX_REBOOT_CMD_RESTART2
105 The "init" process is terminated, and wait(2) in the parent
106 process reports that the child was killed with a SIGHUP signal.
107 LINUX_REBOOT_CMD_POWER_OFF, LINUX_REBOOT_CMD_HALT
109 The "init" process is terminated, and wait(2) in the parent
110 process reports that the child was killed with a SIGINT signal.
111 For the other cmd values, reboot() returns -1 and errno is set to EIN‐
113 VAL.
114
116 For the values of cmd that stop or restart the system, a successful
117 call to reboot() does not return. For the other cmd values, zero is
118 returned on success. In all cases, -1 is returned on failure, and er‐
119 rno is set appropriately.
120
122 EFAULT Problem with getting user-space data under LINUX_RE‐
123 BOOT_CMD_RESTART2.
124 EINVAL Bad magic numbers or cmd.
126 EPERM The calling process has insufficient privilege to call reboot();
128 the caller must have the CAP_SYS_BOOT inside its user namespace.
129
131 reboot() is Linux-specific, and should not be used in programs intended
132 to be portable.
133
135 systemctl(1), systemd(1), kexec_load(2), sync(2), bootparam(7), capa‐
136 bilities(7), ctrlaltdel(8), halt(8), shutdown(8)
137
139 This page is part of release 5.10 of the Linux man-pages project. A
140 description of the project, information about reporting bugs, and the
141 latest version of this page, can be found at
142 https://www.kernel.org/doc/man-pages/.
143Linux 2019-03-06 REBOOT(2)