man/systemd-halt.service.8

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  22 .SH "NAME"
  23 systemd-halt.service, systemd-poweroff.service, systemd-reboot.service, systemd-kexec.service, systemd-shutdown \- System shutdown logic
  24 .SH "SYNOPSIS"
  25 .PP
  26 systemd\-halt\&.service
  27 .PP
  28 systemd\-poweroff\&.service
  29 .PP
  30 systemd\-reboot\&.service
  31 .PP
  32 systemd\-kexec\&.service
  33 .PP
  34 /usr/lib/systemd/systemd\-shutdown
  35 .SH "DESCRIPTION"
  36 .PP
  37 systemd\-halt\&.service
  38 is a system service that is pulled in by
  39 halt\&.target
  40 and is responsible for the actual system halt\&. Similarly,
  41 systemd\-poweroff\&.service
  42 is pulled in by
  43 poweroff\&.target,
  44 systemd\-reboot\&.service
  45 by
  46 reboot\&.target
  47 and
  48 systemd\-kexec\&.service
  49 by
  50 kexec\&.target
  51 to execute the respective actions\&.
  52 .PP
  53 When these services are run, they ensure that PID 1 is replaced by the
  54 /usr/lib/systemd/systemd\-shutdown
  55 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\&.
  56 .PP
  57 It is necessary to have this code in a separate binary because otherwise rebooting after an upgrade might be broken\ \&\(em 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\&.
  58 .PP
  59 Immediately before executing the actual system halt/poweroff/reboot/kexec
  60 systemd\-shutdown
  61 will run all executables in
  62 /usr/lib/systemd/system\-shutdown/
  63 and pass one arguments to them: either
  64 "halt",
  65 "poweroff",
  66 "reboot"
  67 or
  68 "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\&.
  69 .PP
  70 Note that
  71 systemd\-halt\&.service
  72 (and the related units) should never be executed directly\&. Instead, trigger system shutdown with a command such as
  73 "systemctl halt"
  74 or suchlike\&.
  75 .SH "SEE ALSO"
  76 .PP
  77 \fBsystemd\fR(1),
  78 \fBsystemctl\fR(1),
  79 \fBsystemd.special\fR(7),
  80 \fBreboot\fR(2),
  81 \fBsystemd-suspend.service\fR(8)