(ntp-check)=

# NTP Checks

Ensure that NTP is properly set up on all nodes. Particularly for Cassandra **DO NOT** use anything else other than ntp. Here are some helpful blogs that explain why:

> - <https://blog.rapid7.com/2014/03/14/synchronizing-clocks-in-a-cassandra-cluster-pt-1-the-problem/>
> - <https://www.digitalocean.com/community/tutorials/how-to-set-up-time-synchronization-on-ubuntu-16-04>

## How can I see if NTP is correctly set up?

This is an important part of your setup, particularly for your Cassandra nodes. You should use `ntpd` and our ansible scripts to ensure it is installed correctly - but you can still check it manually if you prefer. The following 2 sub-sections explain both approaches.

### I used your ansible scripts and prefer to have automated checks

Then the easiest way is to use [this ansible playbook](https://github.com/wireapp/wire-server-deploy/blob/develop/ansible/cassandra-verify-ntp.yml)

### I am not using ansible and like to SSH into hosts and checking things manually

The following shows how to check for existing servers connected to (assumes `ntpq` is installed)

```sh
ntpq -pn
```

which should yield something like this:

```sh
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 time.example.    .POOL.          16 p    -   64    0    0.000    0.000   0.000
+<IP_ADDR_1>      <IP_ADDR_N>      2 u  498  512  377    0.759    0.039   0.081
*<IP_ADDR_2>      <IP_ADDR_N>      2 u  412  512  377    1.251   -0.670   0.063
```

if your output shows \_ONLY\_ the entry with a `.POOL.` as `refid` and a lot of 0s, something is probably wrong, i.e.:

```sh
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 time.example.    .POOL.          16 p    -   64    0    0.000    0.000   0.000
```

What should you do if this is the case? Ensure that `ntp` is installed and that the servers in the pool (typically at `/etc/ntp.conf`) are reachable.