1reboot(2) System Calls Manual reboot(2)
2
6 reboot - reboot or enable/disable Ctrl-Alt-Del
7
9 Standard C library (libc, -lc)
10
12 /* Since Linux 2.1.30 there are symbolic names LINUX_REBOOT_*
13 for the constants and a fourth argument to the call: */
14 #include <linux/reboot.h> /* Definition of LINUX_REBOOT_* constants */
16 #include <sys/syscall.h> /* Definition of SYS_* constants */
17 #include <unistd.h>
18 int syscall(SYS_reboot, int magic, int magic2, int cmd, void *arg);
20 /* Under glibc and most alternative libc's (including uclibc, dietlibc,
22 musl and a few others), some of the constants involved have gotten
23 symbolic names RB_*, and the library call is a 1-argument
24 wrapper around the system call: */
25 #include <sys/reboot.h> /* Definition of RB_* constants */
27 #include <unistd.h>
28 int reboot(int cmd);
30
32 The reboot() call reboots the system, or enables/disables the reboot
33 keystroke (abbreviated CAD, since the default is Ctrl-Alt-Delete; it
34 can be changed using loadkeys(1)).
35 This system call fails (with the error EINVAL) unless magic equals
37 LINUX_REBOOT_MAGIC1 (that is, 0xfee1dead) and magic2 equals LINUX_RE‐
38 BOOT_MAGIC2 (that is, 0x28121969). However, since Linux 2.1.17 also
39 LINUX_REBOOT_MAGIC2A (that is, 0x05121996) and since Linux 2.1.97 also
40 LINUX_REBOOT_MAGIC2B (that is, 0x16041998) and since Linux 2.5.71 also
41 LINUX_REBOOT_MAGIC2C (that is, 0x20112000) are permitted as values for
42 magic2. (The hexadecimal values of these constants are meaningful.)
43 The cmd argument can have the following values:
45 LINUX_REBOOT_CMD_CAD_OFF
47 (RB_DISABLE_CAD, 0). CAD is disabled. This means that the CAD
48 keystroke will cause a SIGINT signal to be sent to init (process
49 1), whereupon this process may decide upon a proper action
50 (maybe: kill all processes, sync, reboot).
51 LINUX_REBOOT_CMD_CAD_ON
53 (RB_ENABLE_CAD, 0x89abcdef). CAD is enabled. This means that
54 the CAD keystroke will immediately cause the action associated
55 with LINUX_REBOOT_CMD_RESTART.
56 LINUX_REBOOT_CMD_HALT
58 (RB_HALT_SYSTEM, 0xcdef0123; since Linux 1.1.76). The message
59 "System halted." is printed, and the system is halted. Control
60 is given to the ROM monitor, if there is one. If not preceded
61 by a sync(2), data will be lost.
62 LINUX_REBOOT_CMD_KEXEC
64 (RB_KEXEC, 0x45584543, since Linux 2.6.13). Execute a kernel
65 that has been loaded earlier with kexec_load(2). This option is
66 available only if the kernel was configured with CONFIG_KEXEC.
67 LINUX_REBOOT_CMD_POWER_OFF
69 (RB_POWER_OFF, 0x4321fedc; since Linux 2.1.30). The message
70 "Power down." is printed, the system is stopped, and all power
71 is removed from the system, if possible. If not preceded by a
72 sync(2), data will be lost.
73 LINUX_REBOOT_CMD_RESTART
75 (RB_AUTOBOOT, 0x1234567). The message "Restarting system." is
76 printed, and a default restart is performed immediately. If not
77 preceded by a sync(2), data will be lost.
78 LINUX_REBOOT_CMD_RESTART2
80 (0xa1b2c3d4; since Linux 2.1.30). The message "Restarting sys‐
81 tem with command '%s'" is printed, and a restart (using the com‐
82 mand string given in arg) is performed immediately. If not pre‐
83 ceded by a sync(2), data will be lost.
84 LINUX_REBOOT_CMD_SW_SUSPEND
86 (RB_SW_SUSPEND, 0xd000fce1; since Linux 2.5.18). The system is
87 suspended (hibernated) to disk. This option is available only
88 if the kernel was configured with CONFIG_HIBERNATION.
89 Only the superuser may call reboot().
91 The precise effect of the above actions depends on the architecture.
93 For the i386 architecture, the additional argument does not do anything
94 at present (2.1.122), but the type of reboot can be determined by ker‐
95 nel command-line arguments ("reboot=...") to be either warm or cold,
96 and either hard or through the BIOS.
97 Behavior inside PID namespaces
99 Since Linux 3.4, if reboot() is called from a PID namespace other than
100 the initial PID namespace with one of the cmd values listed below, it
101 performs a "reboot" of that namespace: the "init" process of the PID
102 namespace is immediately terminated, with the effects described in
103 pid_namespaces(7).
104 The values that can be supplied in cmd when calling reboot() in this
106 case are as follows:
107 LINUX_REBOOT_CMD_RESTART, LINUX_REBOOT_CMD_RESTART2
109 The "init" process is terminated, and wait(2) in the parent
110 process reports that the child was killed with a SIGHUP signal.
111 LINUX_REBOOT_CMD_POWER_OFF, LINUX_REBOOT_CMD_HALT
113 The "init" process is terminated, and wait(2) in the parent
114 process reports that the child was killed with a SIGINT signal.
115 For the other cmd values, reboot() returns -1 and errno is set to EIN‐
117 VAL.
118
120 For the values of cmd that stop or restart the system, a successful
121 call to reboot() does not return. For the other cmd values, zero is
122 returned on success. In all cases, -1 is returned on failure, and er‐
123 rno is set to indicate the error.
124
126 EFAULT Problem with getting user-space data under LINUX_RE‐
127 BOOT_CMD_RESTART2.
128 EINVAL Bad magic numbers or cmd.
130 EPERM The calling process has insufficient privilege to call reboot();
132 the caller must have the CAP_SYS_BOOT inside its user namespace.
133
135 Linux.
136
138 systemctl(1), systemd(1), kexec_load(2), sync(2), bootparam(7), capa‐
139 bilities(7), ctrlaltdel(8), halt(8), shutdown(8)
140Linux man-pages 6.04 2023-03-30 reboot(2)