Why is there a `systemd` process owned by each user that is logged in?

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In my ps output:



root 1 0.0 0.0 225552 5316 ? Ss /lib/systemd/systemd --system --deserialize 19
message+ 572 0.0 0.0 51564 3076 ? Ss /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
root 590 0.0 0.0 71084 2084 ? Ss /lib/systemd/systemd-logind
t 929 0.0 0.0 76872 1988 ? Ss /lib/systemd/systemd --user
t 980 0.0 0.0 50792 2688 ? Ss /usr/bin/dbus-daemon --session --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
systemd+ 2632 0.0 0.0 71240 2464 ? Ss /lib/systemd/systemd-resolved
systemd+ 2637 0.0 0.0 143976 712 ? Ssl /lib/systemd/systemd-timesyncd
root 2642 0.0 0.4 232544 37308 ? S<s /lib/systemd/systemd-journald
root 3334 0.0 0.0 46108 2252 ? Ss /lib/systemd/systemd-udevd
testme 22693 0.0 0.0 76964 3428 ? Ss /lib/systemd/systemd --user


Why do I have so many systemd related processes?



In particular, why is there a systemd process owned by each user that is logged in?



In the boot sequence of Linux, the kernel starts the init system as the first process, and then the init process runs login so that each user can login. I think the init system should be run as as a singleton process, regardless of how many users login, and regardless of whether the init system is sysvinit or systemd, correct?



Does root have to log in to start its systemd process?



For those systemd processes not owned by root, are they run as daemons?



Thanks.










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    0














    In my ps output:



    root 1 0.0 0.0 225552 5316 ? Ss /lib/systemd/systemd --system --deserialize 19
    message+ 572 0.0 0.0 51564 3076 ? Ss /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
    root 590 0.0 0.0 71084 2084 ? Ss /lib/systemd/systemd-logind
    t 929 0.0 0.0 76872 1988 ? Ss /lib/systemd/systemd --user
    t 980 0.0 0.0 50792 2688 ? Ss /usr/bin/dbus-daemon --session --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
    systemd+ 2632 0.0 0.0 71240 2464 ? Ss /lib/systemd/systemd-resolved
    systemd+ 2637 0.0 0.0 143976 712 ? Ssl /lib/systemd/systemd-timesyncd
    root 2642 0.0 0.4 232544 37308 ? S<s /lib/systemd/systemd-journald
    root 3334 0.0 0.0 46108 2252 ? Ss /lib/systemd/systemd-udevd
    testme 22693 0.0 0.0 76964 3428 ? Ss /lib/systemd/systemd --user


    Why do I have so many systemd related processes?



    In particular, why is there a systemd process owned by each user that is logged in?



    In the boot sequence of Linux, the kernel starts the init system as the first process, and then the init process runs login so that each user can login. I think the init system should be run as as a singleton process, regardless of how many users login, and regardless of whether the init system is sysvinit or systemd, correct?



    Does root have to log in to start its systemd process?



    For those systemd processes not owned by root, are they run as daemons?



    Thanks.










    share|improve this question


























      0












      0








      0







      In my ps output:



      root 1 0.0 0.0 225552 5316 ? Ss /lib/systemd/systemd --system --deserialize 19
      message+ 572 0.0 0.0 51564 3076 ? Ss /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
      root 590 0.0 0.0 71084 2084 ? Ss /lib/systemd/systemd-logind
      t 929 0.0 0.0 76872 1988 ? Ss /lib/systemd/systemd --user
      t 980 0.0 0.0 50792 2688 ? Ss /usr/bin/dbus-daemon --session --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
      systemd+ 2632 0.0 0.0 71240 2464 ? Ss /lib/systemd/systemd-resolved
      systemd+ 2637 0.0 0.0 143976 712 ? Ssl /lib/systemd/systemd-timesyncd
      root 2642 0.0 0.4 232544 37308 ? S<s /lib/systemd/systemd-journald
      root 3334 0.0 0.0 46108 2252 ? Ss /lib/systemd/systemd-udevd
      testme 22693 0.0 0.0 76964 3428 ? Ss /lib/systemd/systemd --user


      Why do I have so many systemd related processes?



      In particular, why is there a systemd process owned by each user that is logged in?



      In the boot sequence of Linux, the kernel starts the init system as the first process, and then the init process runs login so that each user can login. I think the init system should be run as as a singleton process, regardless of how many users login, and regardless of whether the init system is sysvinit or systemd, correct?



      Does root have to log in to start its systemd process?



      For those systemd processes not owned by root, are they run as daemons?



      Thanks.










      share|improve this question















      In my ps output:



      root 1 0.0 0.0 225552 5316 ? Ss /lib/systemd/systemd --system --deserialize 19
      message+ 572 0.0 0.0 51564 3076 ? Ss /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
      root 590 0.0 0.0 71084 2084 ? Ss /lib/systemd/systemd-logind
      t 929 0.0 0.0 76872 1988 ? Ss /lib/systemd/systemd --user
      t 980 0.0 0.0 50792 2688 ? Ss /usr/bin/dbus-daemon --session --address=systemd: --nofork --nopidfile --systemd-activation --syslog-only
      systemd+ 2632 0.0 0.0 71240 2464 ? Ss /lib/systemd/systemd-resolved
      systemd+ 2637 0.0 0.0 143976 712 ? Ssl /lib/systemd/systemd-timesyncd
      root 2642 0.0 0.4 232544 37308 ? S<s /lib/systemd/systemd-journald
      root 3334 0.0 0.0 46108 2252 ? Ss /lib/systemd/systemd-udevd
      testme 22693 0.0 0.0 76964 3428 ? Ss /lib/systemd/systemd --user


      Why do I have so many systemd related processes?



      In particular, why is there a systemd process owned by each user that is logged in?



      In the boot sequence of Linux, the kernel starts the init system as the first process, and then the init process runs login so that each user can login. I think the init system should be run as as a singleton process, regardless of how many users login, and regardless of whether the init system is sysvinit or systemd, correct?



      Does root have to log in to start its systemd process?



      For those systemd processes not owned by root, are they run as daemons?



      Thanks.







      systemd init sysvinit






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      edited Dec 19 at 13:16

























      asked Dec 19 at 13:06









      Tim

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          The init process is pid 1, and root most certainly doesn’t have to log in to start it. The other processes aren’t the init process.



          The various per-user systemd processes manage each user’s services. These include user services (systemctl --user start ...), and a number of “per-user dæmons” (in GNOME, you’ll see PulseAudio, various GVFS processes, etc.).



          The other systemd processes handle specific services: the resolver, the time synchronisation service, the journal, etc.



          Your ps output shows that none of these processes has a controlling terminal, so they’re all running as dæmons (for some value of dæmon).



          systemd has very good documentation, try man systemd, man systemd-logind etc.






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            1 Answer
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            active

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            The init process is pid 1, and root most certainly doesn’t have to log in to start it. The other processes aren’t the init process.



            The various per-user systemd processes manage each user’s services. These include user services (systemctl --user start ...), and a number of “per-user dæmons” (in GNOME, you’ll see PulseAudio, various GVFS processes, etc.).



            The other systemd processes handle specific services: the resolver, the time synchronisation service, the journal, etc.



            Your ps output shows that none of these processes has a controlling terminal, so they’re all running as dæmons (for some value of dæmon).



            systemd has very good documentation, try man systemd, man systemd-logind etc.






            share|improve this answer



























              3














              The init process is pid 1, and root most certainly doesn’t have to log in to start it. The other processes aren’t the init process.



              The various per-user systemd processes manage each user’s services. These include user services (systemctl --user start ...), and a number of “per-user dæmons” (in GNOME, you’ll see PulseAudio, various GVFS processes, etc.).



              The other systemd processes handle specific services: the resolver, the time synchronisation service, the journal, etc.



              Your ps output shows that none of these processes has a controlling terminal, so they’re all running as dæmons (for some value of dæmon).



              systemd has very good documentation, try man systemd, man systemd-logind etc.






              share|improve this answer

























                3












                3








                3






                The init process is pid 1, and root most certainly doesn’t have to log in to start it. The other processes aren’t the init process.



                The various per-user systemd processes manage each user’s services. These include user services (systemctl --user start ...), and a number of “per-user dæmons” (in GNOME, you’ll see PulseAudio, various GVFS processes, etc.).



                The other systemd processes handle specific services: the resolver, the time synchronisation service, the journal, etc.



                Your ps output shows that none of these processes has a controlling terminal, so they’re all running as dæmons (for some value of dæmon).



                systemd has very good documentation, try man systemd, man systemd-logind etc.






                share|improve this answer














                The init process is pid 1, and root most certainly doesn’t have to log in to start it. The other processes aren’t the init process.



                The various per-user systemd processes manage each user’s services. These include user services (systemctl --user start ...), and a number of “per-user dæmons” (in GNOME, you’ll see PulseAudio, various GVFS processes, etc.).



                The other systemd processes handle specific services: the resolver, the time synchronisation service, the journal, etc.



                Your ps output shows that none of these processes has a controlling terminal, so they’re all running as dæmons (for some value of dæmon).



                systemd has very good documentation, try man systemd, man systemd-logind etc.







                share|improve this answer














                share|improve this answer



                share|improve this answer








                edited Dec 19 at 13:19

























                answered Dec 19 at 13:14









                Stephen Kitt

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                164k24365444



























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