CODEWITHSUNDEEP
linuxlinux-kernelsystem-callsreboot
jerryang
jerryang

Reputation: 11

Detailed procedures of linux rebooting

I'm interested in how rebooting is implemented in Linux. When I press ctrl-alt-del or click "restart" in the menu bar, what happens next?

Thanks!

Upvotes: 0

Views: 1318

Answers (3)

PeterS6g
PeterS6g

Reputation: 122

There are different init systems on Linux, and they also control what happens on restart/shutdown. See https://unix.stackexchange.com/questions/18209/detect-init-system-using-the-shell to tell which you're using.

If you're using SysVinit, then there is a runlevel associated with the overall system status. The init system will first run all the kill scripts associated with your current runlevel and then the start scripts associated with runlevel 6. If your current runlevel was 5, it would run /etc/rc5.d/K* and then /etc/rc6.d/S*. They might be in another directory, such as /etc/init.d/rc5.d/k*, depending on your Linux distribution.

If you're using systemd, then instead of having an overall "runlevel", there would be a list of defined targets and services. A list of targets is essentially a runlevel. These are defined in .service and .target files under /etc/systemd. There will likely be a "reboot.target" defined under there, and other services with a dependency on that will be run on reboot. See the systemd homepage or this stackexchange question for an example.

Some Ubuntu versions also use upstart, but I think it's been replaced by systemd in more recent versions. If you are using upstart, see this guide or this askubuntu question.

One thing to be careful of is that regardless of which init system you're using you may be using init scripts generally associated with another one. So you may be using sysVinit, but some of the rc*.d scripts may be links to things that invoke systemd scripts. Or vice-versa.

Upvotes: 0

J-L
J-L

Reputation: 199

Quick answer is that all the scripts that are in /etc/rc6.d are executed.

scripts that start with "K" are executed with the "stop" parameter. scripts that start with "S" are executed with the "start"parameter.

For more you can start reading about runlevels here: http://en.wikipedia.org/wiki/Runlevel

Upvotes: 0

marian craciunescu
marian craciunescu

Reputation: 11

brings the system down in a secure way. All logged-in users are notified that the system is going down, and login(1) is blocked. It is possible to shut the system down immediately or after a specified delay. All processes are first notified that the system is going down by the signal SIGTERM. It does its job by signalling the init process, asking it to change the runlevel. Runlevel 0 is used to halt the system, runlevel 6 is used to reboot the system, and runlevel 1 is used to put to system into a state where administrative tasks can be performed; So basically reboot calls the "shutdown".

Upvotes: 1

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