383 lines
8.8 KiB
HTML
383 lines
8.8 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of REBOOT</TITLE>
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</HEAD><BODY>
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<H1>REBOOT</H1>
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Section: Linux Programmer's Manual (2)<BR>Updated: 2019-03-06<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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reboot - reboot or enable/disable Ctrl-Alt-Del
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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/* Since kernel version 2.1.30 there are symbolic names LINUX_REBOOT_*
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<BR> for the constants and a fourth argument to the call: */
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<P>
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<B>#include <<A HREF="file:///usr/include/unistd.h">unistd.h</A>></B>
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<BR>
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<B>#include <<A HREF="file:///usr/include/linux/reboot.h">linux/reboot.h</A>></B>
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<P>
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<B>int reboot(int </B><I>magic</I><B>, int </B><I>magic2</I><B>, int </B><I>cmd</I><B>, void *</B><I>arg</I><B>);</B>
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<P>
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/* Under glibc and most alternative libc's (including uclibc, dietlibc,
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<BR> musl and a few others), some of the constants involved have gotten
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<BR> symbolic names RB_*, and the library call is a 1-argument
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<BR> wrapper around the system call: */
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<P>
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<B>#include <<A HREF="file:///usr/include/unistd.h">unistd.h</A>></B>
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<BR>
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<B>#include <<A HREF="file:///usr/include/sys/reboot.h">sys/reboot.h</A>></B>
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<P>
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<B>int reboot(int </B><I>cmd</I><B>);</B>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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The
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<B>reboot</B>()
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call reboots the system, or enables/disables the reboot keystroke
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(abbreviated CAD, since the default is Ctrl-Alt-Delete;
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it can be changed using
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<B><A HREF="/cgi-bin/man/man2html?1+loadkeys">loadkeys</A></B>(1)).
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<P>
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This system call fails (with the error
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<B>EINVAL</B>)
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unless
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<I>magic</I>
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equals
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<B>LINUX_REBOOT_MAGIC1</B>
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(that is, 0xfee1dead) and
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<I>magic2</I>
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equals
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<B>LINUX_REBOOT_MAGIC2</B>
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(that is, 672274793).
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However, since 2.1.17 also
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<B>LINUX_REBOOT_MAGIC2A</B>
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(that is, 85072278)
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and since 2.1.97 also
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<B>LINUX_REBOOT_MAGIC2B</B>
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(that is, 369367448)
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and since 2.5.71 also
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<B>LINUX_REBOOT_MAGIC2C</B>
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(that is, 537993216)
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are permitted as values for
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<I>magic2</I>.
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(The hexadecimal values of these constants are meaningful.)
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<P>
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The
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<I>cmd</I>
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argument can have the following values:
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<DL COMPACT>
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<DT id="1"><B>LINUX_REBOOT_CMD_CAD_OFF</B>
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<DD>
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(<B>RB_DISABLE_CAD</B>,
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0).
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CAD is disabled.
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This means that the CAD keystroke will cause a
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<B>SIGINT</B>
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signal to be
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sent to init (process 1), whereupon this process may decide upon a
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proper action (maybe: kill all processes, sync, reboot).
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<DT id="2"><B>LINUX_REBOOT_CMD_CAD_ON</B>
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<DD>
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(<B>RB_ENABLE_CAD</B>,
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0x89abcdef).
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CAD is enabled.
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This means that the CAD keystroke will immediately cause
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the action associated with
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<B>LINUX_REBOOT_CMD_RESTART</B>.
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<DT id="3"><B>LINUX_REBOOT_CMD_HALT</B>
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<DD>
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(<B>RB_HALT_SYSTEM</B>,
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0xcdef0123; since Linux 1.1.76).
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The message "System halted." is printed, and the system is halted.
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Control is given to the ROM monitor, if there is one.
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If not preceded by a
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<B><A HREF="/cgi-bin/man/man2html?2+sync">sync</A></B>(2),
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data will be lost.
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<DT id="4"><B>LINUX_REBOOT_CMD_KEXEC</B>
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<DD>
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(<B>RB_KEXEC</B>,
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0x45584543, since Linux 2.6.13).
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Execute a kernel that has been loaded earlier with
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<B><A HREF="/cgi-bin/man/man2html?2+kexec_load">kexec_load</A></B>(2).
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This option is available only if the kernel was configured with
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<B>CONFIG_KEXEC</B>.
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<DT id="5"><B>LINUX_REBOOT_CMD_POWER_OFF</B>
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<DD>
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(<B>RB_POWER_OFF</B>,
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0x4321fedc; since Linux 2.1.30).
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The message "Power down." is printed, the system is stopped,
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and all power is removed from the system, if possible.
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If not preceded by a
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<B><A HREF="/cgi-bin/man/man2html?2+sync">sync</A></B>(2),
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data will be lost.
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<DT id="6"><B>LINUX_REBOOT_CMD_RESTART</B>
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<DD>
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(<B>RB_AUTOBOOT</B>,
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0x1234567).
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The message "Restarting system." is printed, and a default
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restart is performed immediately.
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If not preceded by a
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<B><A HREF="/cgi-bin/man/man2html?2+sync">sync</A></B>(2),
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data will be lost.
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<DT id="7"><B>LINUX_REBOOT_CMD_RESTART2</B>
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<DD>
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(0xa1b2c3d4; since Linux 2.1.30).
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The message "Restarting system with command '%s'" is printed,
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and a restart (using the command string given in
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<I>arg</I>)
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is performed immediately.
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If not preceded by a
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<B><A HREF="/cgi-bin/man/man2html?2+sync">sync</A></B>(2),
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data will be lost.
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<DT id="8"><B>LINUX_REBOOT_CMD_SW_SUSPEND</B>
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<DD>
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(<B>RB_SW_SUSPEND</B>,
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0xd000fce1; since Linux 2.5.18).
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The system is suspended (hibernated) to disk.
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This option is available only if the kernel was configured with
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<B>CONFIG_HIBERNATION</B>.
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</DL>
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<P>
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Only the superuser may call
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<B>reboot</B>().
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<P>
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The precise effect of the above actions depends on the architecture.
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For the i386 architecture, the additional argument does not do
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anything at present (2.1.122), but the type of reboot can be
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determined by kernel command-line arguments ("reboot=...") to be
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either warm or cold, and either hard or through the BIOS.
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<A NAME="lbAE"> </A>
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<H3>Behavior inside PID namespaces</H3>
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Since Linux 3.4,
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if
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<B>reboot</B>()
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is called
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from a PID namespace other than the initial PID namespace
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with one of the
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<I>cmd</I>
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values listed below,
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it performs a "reboot" of that namespace:
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the "init" process of the PID namespace is immediately terminated,
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with the effects described in
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<B><A HREF="/cgi-bin/man/man2html?7+pid_namespaces">pid_namespaces</A></B>(7).
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<P>
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The values that can be supplied in
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<I>cmd</I>
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when calling
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<B>reboot</B>()
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in this case are as follows:
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<DL COMPACT>
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<DT id="9"><B>LINUX_REBOOT_CMD_RESTART</B>, <B>LINUX_REBOOT_CMD_RESTART2</B>
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<DD>
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The "init" process is terminated,
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and
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<B><A HREF="/cgi-bin/man/man2html?2+wait">wait</A></B>(2)
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in the parent process reports that the child was killed with a
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<B>SIGHUP</B>
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signal.
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<DT id="10"><B>LINUX_REBOOT_CMD_POWER_OFF</B>, <B>LINUX_REBOOT_CMD_HALT</B>
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<DD>
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The "init" process is terminated,
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and
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<B><A HREF="/cgi-bin/man/man2html?2+wait">wait</A></B>(2)
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in the parent process reports that the child was killed with a
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<B>SIGINT</B>
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signal.
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</DL>
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<P>
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For the other
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<I>cmd</I>
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values,
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<B>reboot</B>()
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returns -1 and
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<I>errno</I>
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is set to
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<B>EINVAL</B>.
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<A NAME="lbAF"> </A>
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<H2>RETURN VALUE</H2>
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For the values of
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<I>cmd</I>
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that stop or restart the system,
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a successful call to
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<B>reboot</B>()
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does not return.
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For the other
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<I>cmd</I>
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values, zero is returned on success.
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In all cases, -1 is returned on failure, and
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<I>errno</I>
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is set appropriately.
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<A NAME="lbAG"> </A>
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<H2>ERRORS</H2>
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<DL COMPACT>
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<DT id="11"><B>EFAULT</B>
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<DD>
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Problem with getting user-space data under
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<B>LINUX_REBOOT_CMD_RESTART2</B>.
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<DT id="12"><B>EINVAL</B>
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<DD>
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Bad magic numbers or <I>cmd</I>.
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<DT id="13"><B>EPERM</B>
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<DD>
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The calling process has insufficient privilege to call
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<B>reboot</B>();
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the caller must have the
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<B>CAP_SYS_BOOT</B>
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inside its user namespace.
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</DL>
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<A NAME="lbAH"> </A>
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<H2>CONFORMING TO</H2>
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<B>reboot</B>()
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is Linux-specific,
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and should not be used in programs intended to be portable.
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<A NAME="lbAI"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?1+systemctl">systemctl</A></B>(1),
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<B><A HREF="/cgi-bin/man/man2html?1+systemd">systemd</A></B>(1),
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<B><A HREF="/cgi-bin/man/man2html?2+kexec_load">kexec_load</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+sync">sync</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?7+bootparam">bootparam</A></B>(7),
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<B><A HREF="/cgi-bin/man/man2html?7+capabilities">capabilities</A></B>(7),
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<B><A HREF="/cgi-bin/man/man2html?8+ctrlaltdel">ctrlaltdel</A></B>(8),
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<B><A HREF="/cgi-bin/man/man2html?8+halt">halt</A></B>(8),
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<B><A HREF="/cgi-bin/man/man2html?8+shutdown">shutdown</A></B>(8)
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<A NAME="lbAJ"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="14"><A HREF="#lbAB">NAME</A><DD>
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<DT id="15"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="16"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DL>
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<DT id="17"><A HREF="#lbAE">Behavior inside PID namespaces</A><DD>
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</DL>
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<DT id="18"><A HREF="#lbAF">RETURN VALUE</A><DD>
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<DT id="19"><A HREF="#lbAG">ERRORS</A><DD>
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<DT id="20"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="21"><A HREF="#lbAI">SEE ALSO</A><DD>
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<DT id="22"><A HREF="#lbAJ">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:34 GMT, March 31, 2021
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</BODY>
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</HTML>
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