1 .\" Copyright (c) 1998 Andries Brouwer (aeb@cwi.nl), 24 September 1998
3 .\" %%%LICENSE_START(VERBATIM)
4 .\" Permission is granted to make and distribute verbatim copies of this
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8 .\" Permission is granted to copy and distribute modified versions of this
9 .\" manual under the conditions for verbatim copying, provided that the
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13 .\" Since the Linux kernel and libraries are constantly changing, this
14 .\" manual page may be incorrect or out-of-date. The author(s) assume no
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18 .\" which is licensed free of charge, as they might when working
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25 .\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com>
26 .\" Added notes on capability requirements
28 .TH REBOOT 2 2021-03-22 "Linux" "Linux Programmer's Manual"
30 reboot \- reboot or enable/disable Ctrl-Alt-Del
33 .RB "/* Since kernel version 2.1.30 there are symbolic names " LINUX_REBOOT_*
34 for the constants and a fourth argument to the call: */
36 .BR "#include <linux/reboot.h> " \
37 "/* Definition of " LINUX_REBOOT_* " constants */"
38 .BR "#include <sys/syscall.h> " "/* Definition of " SYS_* " constants */"
39 .B #include <unistd.h>
41 .BI "int syscall(SYS_reboot, int " magic ", int " magic2 ", int " cmd ", void *" arg );
43 /* Under glibc and most alternative libc's (including uclibc, dietlibc,
44 musl and a few others), some of the constants involved have gotten
45 .RB " symbolic names " RB_* ", and the library call is a 1-argument"
46 wrapper around the system call: */
48 .BR "#include <sys/reboot.h> " "/* Definition of " RB_* " constants */"
49 .B #include <unistd.h>
51 .BI "int reboot(int " cmd );
56 call reboots the system, or enables/disables the reboot keystroke
57 (abbreviated CAD, since the default is Ctrl-Alt-Delete;
58 it can be changed using
61 This system call fails (with the error
66 .B LINUX_REBOOT_MAGIC1
67 (that is, 0xfee1dead) and
70 .B LINUX_REBOOT_MAGIC2
72 However, since 2.1.17 also
73 .B LINUX_REBOOT_MAGIC2A
76 .B LINUX_REBOOT_MAGIC2B
79 .B LINUX_REBOOT_MAGIC2C
81 are permitted as values for
83 (The hexadecimal values of these constants are meaningful.)
87 argument can have the following values:
89 .B LINUX_REBOOT_CMD_CAD_OFF
90 .RB ( RB_DISABLE_CAD ,
93 This means that the CAD keystroke will cause a
96 sent to init (process 1), whereupon this process may decide upon a
97 proper action (maybe: kill all processes, sync, reboot).
99 .B LINUX_REBOOT_CMD_CAD_ON
100 .RB ( RB_ENABLE_CAD ,
103 This means that the CAD keystroke will immediately cause
104 the action associated with
105 .BR LINUX_REBOOT_CMD_RESTART .
107 .B LINUX_REBOOT_CMD_HALT
108 .RB ( RB_HALT_SYSTEM ,
109 0xcdef0123; since Linux 1.1.76).
110 The message "System halted." is printed, and the system is halted.
111 Control is given to the ROM monitor, if there is one.
116 .BR LINUX_REBOOT_CMD_KEXEC
118 0x45584543, since Linux 2.6.13).
119 Execute a kernel that has been loaded earlier with
121 This option is available only if the kernel was configured with
124 .B LINUX_REBOOT_CMD_POWER_OFF
126 0x4321fedc; since Linux 2.1.30).
127 The message "Power down." is printed, the system is stopped,
128 and all power is removed from the system, if possible.
133 .B LINUX_REBOOT_CMD_RESTART
136 The message "Restarting system." is printed, and a default
137 restart is performed immediately.
142 .B LINUX_REBOOT_CMD_RESTART2
143 (0xa1b2c3d4; since Linux 2.1.30).
144 The message "Restarting system with command \(aq%s\(aq" is printed,
145 and a restart (using the command string given in
147 is performed immediately.
152 .BR LINUX_REBOOT_CMD_SW_SUSPEND
153 .RB ( RB_SW_SUSPEND ,
154 0xd000fce1; since Linux 2.5.18).
155 The system is suspended (hibernated) to disk.
156 This option is available only if the kernel was configured with
157 .BR CONFIG_HIBERNATION .
159 Only the superuser may call
162 The precise effect of the above actions depends on the architecture.
163 For the i386 architecture, the additional argument does not do
164 anything at present (2.1.122), but the type of reboot can be
165 determined by kernel command-line arguments ("reboot=...") to be
166 either warm or cold, and either hard or through the BIOS.
168 .SS Behavior inside PID namespaces
169 .\" commit cf3f89214ef6a33fad60856bc5ffd7bb2fc4709b
170 .\" see also commit 923c7538236564c46ee80c253a416705321f13e3
175 from a PID namespace other than the initial PID namespace
179 it performs a "reboot" of that namespace:
180 the "init" process of the PID namespace is immediately terminated,
181 with the effects described in
182 .BR pid_namespaces (7).
184 The values that can be supplied in
188 in this case are as follows:
190 .BR LINUX_REBOOT_CMD_RESTART ", " LINUX_REBOOT_CMD_RESTART2
191 The "init" process is terminated,
194 in the parent process reports that the child was killed with a
198 .BR LINUX_REBOOT_CMD_POWER_OFF ", " LINUX_REBOOT_CMD_HALT
199 The "init" process is terminated,
202 in the parent process reports that the child was killed with a
217 that stop or restart the system,
223 values, zero is returned on success.
224 In all cases, \-1 is returned on failure, and
226 is set to indicate the error.
230 Problem with getting user-space data under
231 .BR LINUX_REBOOT_CMD_RESTART2 .
234 Bad magic numbers or \fIcmd\fP.
237 The calling process has insufficient privilege to call
239 the caller must have the
241 inside its user namespace.
245 and should not be used in programs intended to be portable.
252 .BR capabilities (7),