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shutdown(8) [centos man page]

SHUTDOWN(8)							     shutdown							       SHUTDOWN(8)

NAME
shutdown - Halt, power-off or reboot the machine SYNOPSIS
shutdown [OPTIONS...] [TIME] [WALL...] DESCRIPTION
shutdown may be used to halt, power-off or reboot the machine. The first argument may be a time string (which is usually "now"). Optionally, this may be followed by a wall message to be sent to all logged-in users before going down. The time string may either be in the format "hh:mm" for hour/minutes specifying the time to execute the shutdown at, specified in 24h clock format. Alternatively it may be in the syntax "+m" referring to the specified number of minutes m from now. "now" is an alias for "+0", i.e. for triggering an immediate shutdown. If no time argument is specified, "+1" is implied. Note that to specify a wall message you must specify a time argument, too. If the time argument is used, 5 minutes before the system goes down the /run/nologin file is created to ensure that further logins shall not be allowed. OPTIONS
The following options are understood: --help Prints a short help text and exits. -H, --halt Halt the machine. -P, --poweroff Power-off the machine (the default). -r, --reboot Reboot the machine. -h Equivalent to --poweroff, unless --halt is specified. -k Do not halt, power-off, reboot, just write wall message. --no-wall Do not send wall message before halt, power-off, reboot. -c Cancel a pending shutdown. This may be used cancel the effect of an invocation of shutdown with a time argument that is not "+0" or "now". EXIT STATUS
On success, 0 is returned, a non-zero failure code otherwise. SEE ALSO
systemd(1), systemctl(1), halt(8), wall(1) systemd 208 SHUTDOWN(8)

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SYSTEMD-HALT.SERVICE(8) 				       systemd-halt.service					   SYSTEMD-HALT.SERVICE(8)

NAME
systemd-halt.service, systemd-poweroff.service, systemd-reboot.service, systemd-kexec.service, systemd-shutdown - System shutdown logic SYNOPSIS
systemd-halt.service systemd-poweroff.service systemd-reboot.service systemd-kexec.service /lib/systemd/systemd-shutdown /lib/systemd/system-shutdown/ DESCRIPTION
systemd-halt.service is a system service that is pulled in by halt.target and is responsible for the actual system halt. Similarly, systemd-poweroff.service is pulled in by poweroff.target, systemd-reboot.service by reboot.target and systemd-kexec.service by kexec.target to execute the respective actions. When these services are run, they ensure that PID 1 is replaced by the /lib/systemd/systemd-shutdown tool which is then responsible for the actual shutdown. Before shutting down, this binary will try to unmount all remaining file systems, disable all remaining swap devices, detach all remaining storage devices and kill all remaining processes. It is necessary to have this code in a separate binary because otherwise rebooting after an upgrade might be broken -- the running PID 1 could still depend on libraries which are not available any more, thus keeping the file system busy, which then cannot be re-mounted read-only. Immediately before executing the actual system halt/poweroff/reboot/kexec systemd-shutdown will run all executables in /lib/systemd/system-shutdown/ and pass one arguments to them: either "halt", "poweroff", "reboot" or "kexec", depending on the chosen action. All executables in this directory are executed in parallel, and execution of the action is not continued before all executables finished. Note that systemd-halt.service (and the related units) should never be executed directly. Instead, trigger system shutdown with a command such as "systemctl halt" or suchlike. SEE ALSO
systemd(1), systemctl(1), systemd.special(7), reboot(2), systemd-suspend.service(8) systemd 237 SYSTEMD-HALT.SERVICE(8)

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