Add til for setting up a ntp server on linux

linux/ntp-server.md

@@ -0,0 +1,137 @@
+https://linuxconfig.org/ubuntu-22-04-ntp-server
+
+## Install NTP server
+
+To begin, we need to install NTP server. You can do so by [opening a command line terminal](https://linuxconfig.org/how-to-open-a-terminal-on-ubuntu-xenial-xerus-16-04-linux) and entering the following command:
+
+```
+$ sudo apt update
+$ sudo apt install ntp
+```
+
+## Configure NTP server
+
+The NTP server comes pre-configured with some server pools already, which you can see inside the `/etc/ntp.conf` file.
+
+```
+$ cat /etc/ntp.conf
+```
+
+[![The default server pools inside our NTP config file](https://linuxconfig.org/wp-content/uploads/2022/04/01-ubuntu-22-04-ntp-server.png)](https://linuxconfig.org/wp-content/uploads/2022/04/01-ubuntu-22-04-ntp-server.png)
+
+The default server pools inside our NTP config file
+
+Generally, it's best to replace these lines with server pools from your own country, or at least your own continent. The less latency between you and a time server, the better. You can use the [NTP Pool Project](http://www.pool.ntp.org/zone/@) website to find the closest NTP server pool to your location.
+
+[![Find your closest server pools from the NTP Pool Project website](https://linuxconfig.org/wp-content/uploads/2022/04/02-ubuntu-22-04-ntp-server.png)](https://linuxconfig.org/wp-content/uploads/2022/04/02-ubuntu-22-04-ntp-server.png)
+
+Find your closest server pools from the NTP Pool Project website
+
+Once you find the most relevant zone, all you need to do is add the lines in your config file by using nano or your preferred text editor:
+
+```
+$ sudo nano /etc/ntp.conf
+```
+
+[![Enter the servers into the NTP config file](https://linuxconfig.org/wp-content/uploads/2022/04/03-ubuntu-22-04-ntp-server.png)](https://linuxconfig.org/wp-content/uploads/2022/04/03-ubuntu-22-04-ntp-server.png)
+
+Enter the servers into the NTP config file
+
+Once you've made these changes, save and exit the configuration file. Restart the NTP service for the changes to take effect:
+
+$ sudo systemctl restart ntp
+
+---
+
+Check on the status of the NTP service at any time with this command:
+
+```
+$ sudo systemctl status ntp
+```
+
+[![The status of NTP server daemon](https://linuxconfig.org/wp-content/uploads/2022/04/04-ubuntu-22-04-ntp-server.png)](https://linuxconfig.org/wp-content/uploads/2022/04/04-ubuntu-22-04-ntp-server.png)
+
+The status of NTP server daemon
+
+Clients trying to connect to your NTP server will be doing so on UDP port `123`. If you have the UFW firewall enabled on you system, be sure to configure it to allow these incoming connection requests:
+
+```
+$ sudo ufw allow from any to any port 123 proto udp
+Rules updated
+Rules updated (v6)
+```
+
+## NTP client configuration
+
+Now that we have an NTP server up and running, we will show how client systems can connect to it for time synchronization. Just follow the steps below on your client systems:
+
+1.  First, we need to install the ntpdate package. We can use this to verify connectivity between the client and the NTP time server we created.
+
+    $ sudo apt update
+    $ sudo apt install ntpdate
+
+2.  Next, let's attempt to mantually sync our system time with the NTP server. Type the following command, substituting your NTP server's IP address or hostname where appropriate:
+
+    $ sudo ntpdate 192.168.100.4
+
+    [![Connection to NTP server is successful](https://linuxconfig.org/wp-content/uploads/2022/04/05-ubuntu-22-04-ntp-server.png)](https://linuxconfig.org/wp-content/uploads/2022/04/05-ubuntu-22-04-ntp-server.png)
+
+    Connection to NTP server is successful
+
+3.  That seems to be working as we'd expect. Next, be sure to disable Ubuntu's default `timesyncd` service, as this will conflict with our attempts to synchronize with the NTP server.
+
+    ***
+
+    ***
+
+    $ sudo timedatectl set-ntp off
+
+4.  Now, we need to install the NTP daemon on our client system so we can configure it to pull the time from our NTP server that we set up earlier.
+
+    $ sudo apt install ntp
+
+5.  We only need to add a single line to our `ntp.conf` file, and we can do that very easily with a single command. Just make sure to replace the IP address below with either the hostname or the IP address of your NTP server.
+
+    $ sudo bash -c "echo server 192.168.100.4 prefer iburst >> /etc/ntp.conf"
+
+6.  Then, restart the NTP daemon:
+
+    $ sudo systemctl restart ntp
+
+7.  Lastly, use the `ntpq` command to list the NTP time synchronization queue:
+
+    $ ntpq -p
+
+    [![Output from the ntpq command](https://linuxconfig.org/wp-content/uploads/2022/04/06-ubuntu-22-04-ntp-server.png)](https://linuxconfig.org/wp-content/uploads/2022/04/06-ubuntu-22-04-ntp-server.png)
+
+    Output from the ntpq command
+
+    The asterisk `*` in the screenshot above indicates that our NTP server `192.168.100.4` is selected as the current time synchronization source. This should remain the case unless the NTP server goes offline, as that's how we've configured it inside the `ntp.conf` configuration file.
+
+Read the below appendix for more information on how to interpret the `ntpq` command's output.
+
+## Appendix
+
+**NTPQ Command column output interpretation:**
+
+- **remote** -- The remote server you wish to synchronize your clock with
+- **refid** -- The upstream stratum to the remote server. For stratum 1 servers, this will be the stratum 0 source.
+- **st** -- The stratum level, 0 through 16.
+- **t** -- The type of connection. Can be "u" for unicast or manycast, "b" for broadcast or multicast, "l" for local reference clock, "s" for symmetric peer, "A" for a manycast server, "B" for a broadcast server, or "M" for a multicast server
+- **when** -- The last time when the server was queried for the time. Default is seconds, or "m" will be displayed for minutes, "h" for hours and "d" for days.
+- **poll** -- How often the server is queried for the time, with a minimum of 16 seconds to a maximum of 36 hours. It's also displayed as a value from a power of two. Typically, it's between 64 seconds and 1024 seconds.
+- **reach** -- This is an 8-bit left shift octal value that shows the success and failure rate of communicating with the remote server. Success means the bit is set, failure means the bit is not set. 377 is the highest value.
+- **delay** -- This value is displayed in milliseconds, and shows the round trip time (RTT) of your computer communicating with the remote server.
+- **offset** -- This value is displayed in milliseconds, using root mean squares, and shows how far off your clock is from the reported time the server gave you. It can be positive or negative.
+- **jitter** -- This number is an absolute value in milliseconds, showing the root mean squared deviation of your offsets.
+
+**NTPQ Command row output interpretation:**
+
+- **" "** Discarded as not valid. Could be that you cannot communicate with the remote machine (it's not online), this time source is a ".LOCL." refid time source, it's a high stratum server, or the remote server is using this computer as an NTP server.
+- **x** Discarded by the intersection algorithm.
+- **.** Discarded by table overflow (not used).
+- **--** Discarded by the cluster algorithm.
+- **+** Included in the combine algorithm. This is a good candidate if the current server we are synchronizing with is discarded for any reason.
+- **#** Good remote server to be used as an alternative backup. This is only shown if you have more than 10 remote servers.
+- **\*** The current system peer. The computer is using this remote server as its time source to synchronize the clock
+- **o** Pulse per second (PPS) peer. This is generally used with GPS time sources, although any time source delivering a PPS will do. This tally code and the previous tally code "\*" will not be displayed simultaneously.