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Boris Valderrama
Asked: 2020-12-31 17:26:34 +0800 CST 2020-12-31 17:26:34 +0800 CST

What is the difference between systemctl reboot and reboot?

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I understand that it rebootis to restart the pc, while it systemctl rebootis to do the same thing but with systemd, but I don't know what the difference is when using one or the other

linux

1 Answers

  1. Best Answer

    First I think you have to explain things that seem unrelated.

    systemd , SysVinit are a set of daemons responsible for initializing an operating system and managing system processes after boot.

    systemd , and others like upstart , etc, emerged as a replacement for SysVinit .

    You can see that they are the first processes that are executed.

    ps --pid=1 f
  PID TTY      STAT   TIME COMMAND
    1 ?        Ss     0:00 /init ro

ps --pid=1 f
  PID TTY      STAT   TIME COMMAND
    1 ?        Ss     3:46 /lib/systemd/systemd --system --deserialize 20

    Both have programs (or symbolic links) to work with the management of the system processes. Shut down, stop, restart, system or cancel these tasks.

    rebootWhen programs like or were used on a system using SysVinit, poweroffthese were symbolic links to the program haltand made this program act differently depending on the name it had been invoked on. When they were called, the execution level ( runlevel ) was changed to 1, for single-user mode or maintenance level, and processes were run according to what was stipulated in their execution level scripts.

    Instead, on systems using systemdsystemctl , the controlling program is used systemd.

    Something analogous, to the symbolic links, happens with the program poweroffand others that are used to maintain a relationship with those of SysVinit

    $ ls -l $(command -v "poweroff")
lrwxrwxrwx 1 root root 14 Jul 30 16:31 /sbin/poweroff -> /bin/systemctl
$ ls -l $(command -v "shutdown")
lrwxrwxrwx 1 root root 14 Jul 30 16:31 /sbin/shutdown -> /bin/systemctl
$ ls -l $(command -v "reboot")
lrwxrwxrwx 1 root root 14 Jul 30 16:31 /sbin/reboot -> /bin/systemctl
$ ls -l $(command -v "halt")
lrwxrwxrwx 1 root root 14 Jul 30 16:31 /sbin/halt -> /bin/systemctl
$ ls -l $(command -v "runlevel")
lrwxrwxrwx 1 root root 14 Jul 30 16:31 /sbin/runlevel -> /bin/systemctl
$ ls -l $(command -v "telinit")
lrwxrwxrwx 1 root root 14 Jul 30 16:31 /sbin/telinit -> /bin/systemctl

    They are all symbolic links to the program /bin/systemctl(in the case of a system using systemd).

    Part of the above was to show that "shutting down" or "rebooting" the machine is a process that depends on a set of initialization programs (upstart, systemd, init, etc). So shutting down or restarting are tasks and concepts dependent on each management system.

    Although the short answer would be that you use the command readlink -f $(command -v reboot)where command -v programais a bash built-in that, among several utilities, allows you to display information on how the name of the program passed as a parameter is interpreted. readlinkis a program that resolves filenames or symbolic links, and with the parameter -for -efollows each symbolic link to which the argument refers.

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