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Update documentation
Signed-off-by: David Oberhollenzer <david.oberhollenzer@tele2.at>
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4 changed files with 39 additions and 4 deletions
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@ -7,3 +7,6 @@ service configuration and further, available services.
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See [docs/network.md](docs/network.md) for a description on how to do static
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network configuration with the provided script and service.
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See [docs/swclock.md](docs/swclock.md) for a description on the software pseudo
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RTC implementation for systems that do not have a hardware real time clock.
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@ -113,10 +113,6 @@ For the shutdown and reboot targets, the following services are executed:
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kernels clock from the hardware at bootup, between the `vfs` and `sysinit`
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targets.
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* nft - If enabled, restores net filter table rules during boot.
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* swclock - For systems that don't have a hardware clock, this service
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restores a somewhat usable time from a file during boot.
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* swclocksave - For systems that don't have a hardware clock, this service
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saves the current time to a file during shutdown or reboot.
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* sshd_keygen - A wait type service that generates host keys for the OpenSSH
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server and then disables itself.
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* sshd - Starts an OpenSSH server after the network pseudo service and after
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@ -81,3 +81,14 @@ follows is passed on to `ip route add` or `ip rule add` respectively.
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An additional service is provided that restores the nft rule set from
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`/etc/nftables.rules`.
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# DHCP based network configuration
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If the configure option `--enable-dhcpclient` is set, two services are added.
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The service `dhpcdmaster` launches a global dhcpcd instance.
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For each port that should be configured via DHCP, the service `dhcpcd` needs
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to be enabled manually with the port name as argument. The service the runs
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after the master service and sends a signal to the master to operate on that
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port.
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25
docs/swclock.md
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25
docs/swclock.md
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@ -0,0 +1,25 @@
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# Software Pseudo RTC
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If the configure flag `--enable-swclock` is set, a few service and cron jobs
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are enabled that try to help with systems that don't have a hardware real
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time clock.
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The software pseudo RTC uses a file in `/var/lib` (exact path can be
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configured) as backing store for the current date and time.
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When booting the system, a service called `swclock` restores the current time
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from the file. When performing a reboot or shutdown, a service called
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`swclocksave` writes the current time back to the file.
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A cron job is enabled that writes the current time to the backing file hourly,
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so in case the system momentarily loses power, it loses "only" up to one hour.
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The time will drift much worse anyway if the system is powered off (even
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intentionally) for a while.
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All this is ensures that the system clock is monotonically increasing and only
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somewhat behind the actual wall clock time.
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To catch up with real time, an additional cron job is enabled that tries to
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update the time from an NTP server every four hours. This functionality is
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implemented in a small shell script, that is also called from a dhcpcd hook
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once a lease is obtained, assuming the DHCP client configure option was set.
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