NervesTime (nerves_time v0.4.9)
View SourceKeep time in sync on Nerves devices
NervesTime
keeps the system clock on Nerves
devices in sync when connected to the network and close to in sync when
disconnected. It's especially useful for devices lacking a Battery-backed
real-time clock and will
advance the clock at startup to a reasonable guess.
Nearly all configuration is via the application config (config.exs
). The
following keys are available:
:servers
- a list of NTP servers for time synchronization. Specifying an empty list turns off NTP:time_file
- a file path for tracking the time. It allows the system to start with a reasonable time quickly on boot and before the Internet is available for NTP to work.:earliest_time
- times before this are considered invalid and adjusted:latest_time
- times after this are considered invalid and adjusted:ntpd
- the absolute path to the Busyboxntpd
. This only needs to be set if your system does not providentpd
in the$PATH
.:await_initialization_timeout
- Timeout to await a successful system time initialization on startup before continuing asynchronously. Set in milliseconds. Defaults to0
.
Summary
Functions
Return the current NTP servers
Manually restart the NTP daemon
Set the list of NTP servers
Set the system time
Check whether NTP is synchronized with the configured NTP servers
Functions
Return the current NTP servers
@spec restart_ntpd() :: :ok | {:error, term()}
Manually restart the NTP daemon
This is normally not necessary since NervesTime
handles restarting it
automatically. An example of a reason to call this function is if you know
when the Internet becomes available. For this case, calling restart_ntp
will cancel ntpd
's internal timeouts and cause it to immediately send time
requests. If using NTP Pool, be sure not to violate its terms of service by
calling this function too frequently.
@spec set_ntp_servers([String.t()]) :: :ok
Set the list of NTP servers
Use this function to replace the list of NTP servers that are queried for
time. It is also possible to set this list in your config.exs
by doing
something like the following:
config :nerves_time, :servers, [
"0.pool.ntp.org",
"1.pool.ntp.org",
"2.pool.ntp.org",
"3.pool.ntp.org"
]
NervesTime
uses NTP Pool by default. To
disable this and configure servers solely at runtime, specify an empty list
in config.exs
:
config :nerves_time, :servers, []
@spec set_system_time(NaiveDateTime.t()) :: :ok | :error
Set the system time
@spec synchronized?() :: boolean()
Check whether NTP is synchronized with the configured NTP servers
It's possible that the time is already set correctly when this returns false.
NervesTime
decides that NTP is synchronized when ntpd
sends a
notification that the device's clock stratum is 4 or less. Clock adjustments
occur before this, though.
Once NTP is synchronized, it will remain that way until the nerves_time
application is restarted.