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# Sincronizzazione del tempo con NTP

NTP è un protocollo TCP/IP per sincronizzare l'ora attraverso la rete: un client richiede l'ora corrente a un server e usa questa per impostare il proprio orologio.

Behind this simple description, there is a lot of complexity - there are tiers of NTP servers, with the tier one NTP servers connected to atomic clocks, and tier two and three servers spreading the load of actually handling requests across the Internet. Also the client software is a lot more complex than you might think - it has to factor out communication delays, and adjust the time in a way that does not upset all the other processes that run on the server. But luckily all that complexity is hidden from you!

Ubuntu uses ntpdate and ntpd.

- ntpdate
- ntpd
- Installazione
- Configurazione
- View status
- Riferimenti

## ntpdate

Ubuntu comes with ntpdate as standard, and will run it once at boot time to set up your time according to Ubuntu's NTP server.

    ntpdate -s ntp.ubuntu.com

## ntpd

The ntp daemon ntpd calculates the drift of your system clock and continuously adjusts it, so there are no large corrections that could lead to inconsistent logs for instance. The cost is a little processing power and memory, but for a modern server this is negligible.

## Installazione

To install ntpd, from a terminal prompt enter:

    sudo apt-get install ntp

## Configurazione

Edit /etc/ntp.conf to add/remove server lines. By default these servers are configured:

    # Use servers from the NTP Pool Project. Approved by Ubuntu Technical Board
    # on 2011-02-08 (LP: #104525). See http://www.pool.ntp.org/join.html for
    # more information.
    server 0.ubuntu.pool.ntp.org
    server 1.ubuntu.pool.ntp.org
    server 2.ubuntu.pool.ntp.org
    server 3.ubuntu.pool.ntp.org

After changing the config file you have to reload the ntpd:

    sudo /etc/init.d/ntp reload

## View status

Use ntpq to see to see more info:

    # sudo ntpq -p
         remote           refid      st t when poll reach   delay   offset  jitter
    ==============================================================================
    +stratum2-2.NTP. 129.70.130.70    2 u    5   64  377   68.461  -44.274 110.334
    +ntp2.m-online.n 212.18.1.106     2 u    5   64  377   54.629  -27.318  78.882
    *145.253.66.170  .DCFa.           1 u   10   64  377   83.607  -30.159  68.343
    +stratum2-3.NTP. 129.70.130.70    2 u    5   64  357   68.795  -68.168 104.612
    +europium.canoni 193.79.237.14    2 u   63   64  337   81.534  -67.968  92.792

## Riferimenti

- See the Ubuntu Time wiki page for more information.

- ntp.org, home of the Network Time Protocol project

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