Systemd Signal Handling

received. This is mostly equivalent to systemctl --user start exit.target --job-mode=replace-irreversibly. SIGINT Upon receiving this signal the systemd system manager will start the ctrl-alt-del.target unit. This is mostly equivalent to systemctl start ctrl-alt-del.target --job-mode=replace-irreversibly. If this signal is received more than 7 times per 2s, an immediate reboot is triggered. Note that pressing Ctrl+Alt+Del on the console will trigger this signal. Hence, if a reboot is hanging, pressing Ctrl+Alt+Del more than 7 times in 2 seconds is a relatively safe way to trigger an immediate reboot. systemd user managers treat this signal the same way as SIGTERM. SIGWINCH When this signal is received the systemd system manager will start the kbrequest.target unit. This is mostly equivalent to systemctl start kbrequest.target. This signal is ignored by systemd user managers. SIGPWR When this signal is received the systemd manager will start the sigpwr.target unit. This is mostly equivalent to systemctl start sigpwr.target. SIGUSR1 When this signal is received the systemd manager will try to reconnect to the D-Bus bus. SIGUSR2 When this signal is received the systemd manager will log its complete state in human-readable form. The data logged is the same as printed by systemd-analyze dump. SIGHUP Reloads the complete daemon configuration. This is mostly equivalent to systemctl daemon-reload. SIGRTMIN+0 Enters default mode, starts the default.target unit. This is mostly equivalent to systemctl isolate default.target. SIGRTMIN+1 Enters rescue mode, starts the rescue.target unit. This is mostly equivalent to systemctl isolate rescue.target. SIGRTMIN+2 Enters emergency mode, starts the emergency.service unit. This is mostly equivalent to systemctl isolate emergency.service. SIGRTMIN+3 Halts the machine, starts the halt.target unit. This is mostly equivalent to systemctl start halt.target --job-mode=replace-irreversibly. SIGRTMIN+4 Powers off the machine, starts the poweroff.target unit. This is mostly equivalent to systemctl start poweroff.target --job-mode=replace-irreversibly. SIGRTMIN+5 Reboots the machine, starts the reboot.target unit. This is mostly equivalent to systemctl start reboot.target --job-mode=replace-irreversibly. SIGRTMIN+6 Reboots the machine via kexec, starts the kexec.target unit. This is mostly equivalent to systemctl start kexec.target --job-mode=replace-irreversibly. SIGRTMIN+13 Immediately halts the machine. SIGRTMIN+14 Immediately powers off the machine. SIGRTMIN+15 Immediately reboots the machine. SIGRTMIN+16 Immediately reboots the machine with kexec. SIGRTMIN+20 Enables display of status messages on the console, as controlled via systemd.show_status=1 on the kernel command line. SIGRTMIN+21 Disables display of status messages on the console, as controlled via systemd.show_status=0 on the kernel command line. SIGRTMIN+22 Sets the service manager's log level to "debug", in a fashion equivalent to systemd.log_level=debug on the kernel command line. SIGRTMIN+23 Restores the log level to its configured value. The configured value is derived from – in order of priority – the value specified with systemd.log-level= on the kernel command line, or the value

This section details how systemd responds to various signals. SIGINT triggers ctrl-alt-del.target or a reboot. SIGWINCH starts kbrequest.target (ignored by user managers). SIGPWR starts sigpwr.target. SIGUSR1 reconnects to D-Bus. SIGUSR2 logs the manager's state. SIGHUP reloads the daemon configuration. Specific SIGRTMIN signals trigger default, rescue, or emergency modes, or halt, power off, reboot, or kexec the machine. Other SIGRTMIN signals control status message display, logging level, and immediate halt/poweroff/reboot actions.