Re: [systemd-devel] systemd and hardware real time clock
W dniu 09.02.2017 o 18:49, Lennart Poettering pisze: > On Thu, 09.02.17 16:14, Michał Zegan (webczat_...@poczta.onet.pl) wrote: > >> Btw, about the argument that the kernel should set rtc time because of >> wrong timestamps in logs, so I should compile the rtc into the kernel: >> let's compare: if I read rtc time during bootup (and rtc is a module), >> timestamps would be bad indeed for some time. >> But one case is, what if there is no rtc? then the kernel cannot read >> the clock. Neither can startup scripts or systemd (if it would ever >> try). so log timestamps would be invalid for far longer, until time is >> synchronized from network, and that will never happen if there is no >> network. So I still think that systemd could do it, or, better, >> initramfs could do it to make all real system logs have a valid >> timestamp, like not sure if initramfs logs are important for anything if >> there were no boot issues. > > Not sure I follow? What precisely do you mean? > > if there's no RTC then the timestamps of all logs before we managed to > get an NTP network fix will always be pretty bad, there's little we > can do about that? Or what are you saying? > > Lennart > Yes, exactly. In addition I was just saying that the above means, that there is nothing bad in letting systemd (or something else after kernel) handle modular rtcs. Because rtc in the kernel still does not cover all possible cases (like missing rtc), and rtcs are very often compiled as modules. Although I now believe initramfs may be a better place for reading hardware clock than systemd running on a real root, that will make proper boot logs have good timestamps I think, only initramfs and the kernel will have timestamp problems. signature.asc Description: OpenPGP digital signature ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] systemd and hardware real time clock
On Thu, 09.02.17 16:14, Michał Zegan (webczat_...@poczta.onet.pl) wrote: > Btw, about the argument that the kernel should set rtc time because of > wrong timestamps in logs, so I should compile the rtc into the kernel: > let's compare: if I read rtc time during bootup (and rtc is a module), > timestamps would be bad indeed for some time. > But one case is, what if there is no rtc? then the kernel cannot read > the clock. Neither can startup scripts or systemd (if it would ever > try). so log timestamps would be invalid for far longer, until time is > synchronized from network, and that will never happen if there is no > network. So I still think that systemd could do it, or, better, > initramfs could do it to make all real system logs have a valid > timestamp, like not sure if initramfs logs are important for anything if > there were no boot issues. Not sure I follow? What precisely do you mean? if there's no RTC then the timestamps of all logs before we managed to get an NTP network fix will always be pretty bad, there's little we can do about that? Or what are you saying? Lennart -- Lennart Poettering, Red Hat ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] systemd and hardware real time clock
W dniu 09.02.2017 o 15:52, Lennart Poettering pisze: > On Tue, 17.01.17 12:29, Michał Zegan (webczat_...@poczta.onet.pl) wrote: > >> Hello. >> >> I am aware of the fact that systemd relies on the kernel to set system >> clock from hardware clock, and that requires compiling rtc drivers into >> the kernel, not as modules. >> I am also aware that doing it othervise would mix timestamps in log entries. >> The question is: if I have rtc driver as a module anyway, how to modify >> initramfs so that system time would be set, in such a way so that it >> happens *before* journald in initramfs starts? I assume it is an >> initramfs using systemd inside of it. >> One approach would be to have an udev rule that does trigger after rtc >> appears or rtc symlink is added, this rule would start a service that >> sets the system clock, but this service would have to always run before >> journald, and that seems not possible in such a configuration, because >> if someone would unplug the rtc the service would not run? >> Another thing is to load rtc and i2c bus module where rtc is connected >> statically without udev detection, and then the hwclock service would >> always be triggered before journald without looking for rtcs appearing... > > Well, you could write a tool that uses libudev but listens on the > kernel mcast group instead of the udev one, and then, as soon as the > RTC showed up would do the /dev/thing. Then, make a service of it, > make sure to use StandardOutput=null + StandardError=null, so that you > don't get an implicit dependency on journald, and order the service > before journald. > > Lennart > Btw, about the argument that the kernel should set rtc time because of wrong timestamps in logs, so I should compile the rtc into the kernel: let's compare: if I read rtc time during bootup (and rtc is a module), timestamps would be bad indeed for some time. But one case is, what if there is no rtc? then the kernel cannot read the clock. Neither can startup scripts or systemd (if it would ever try). so log timestamps would be invalid for far longer, until time is synchronized from network, and that will never happen if there is no network. So I still think that systemd could do it, or, better, initramfs could do it to make all real system logs have a valid timestamp, like not sure if initramfs logs are important for anything if there were no boot issues. signature.asc Description: OpenPGP digital signature ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
Re: [systemd-devel] systemd and hardware real time clock
On Tue, 17.01.17 12:29, Michał Zegan (webczat_...@poczta.onet.pl) wrote: > Hello. > > I am aware of the fact that systemd relies on the kernel to set system > clock from hardware clock, and that requires compiling rtc drivers into > the kernel, not as modules. > I am also aware that doing it othervise would mix timestamps in log entries. > The question is: if I have rtc driver as a module anyway, how to modify > initramfs so that system time would be set, in such a way so that it > happens *before* journald in initramfs starts? I assume it is an > initramfs using systemd inside of it. > One approach would be to have an udev rule that does trigger after rtc > appears or rtc symlink is added, this rule would start a service that > sets the system clock, but this service would have to always run before > journald, and that seems not possible in such a configuration, because > if someone would unplug the rtc the service would not run? > Another thing is to load rtc and i2c bus module where rtc is connected > statically without udev detection, and then the hwclock service would > always be triggered before journald without looking for rtcs appearing... Well, you could write a tool that uses libudev but listens on the kernel mcast group instead of the udev one, and then, as soon as the RTC showed up would do the /dev/thing. Then, make a service of it, make sure to use StandardOutput=null + StandardError=null, so that you don't get an implicit dependency on journald, and order the service before journald. Lennart -- Lennart Poettering, Red Hat ___ systemd-devel mailing list systemd-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/systemd-devel
