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Correct cronyd to chronyd and add a description (#6983) #7265

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Dec 17, 2021
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Correct cronyd to chronyd and add a description (#6983) #7265

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24 changes: 13 additions & 11 deletions check-before-deployment.md
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Original file line number Diff line number Diff line change
Expand Up @@ -111,13 +111,7 @@ Take the `/dev/nvme0n1` data disk as an example:

## Check and disable system swap

This section describes how to disable swap.

TiDB requires sufficient memory space for operation. It is not recommended to use swap as a buffer for insufficient memory, which might reduce performance. Therefore, it is recommended to disable the system swap permanently.

Do not disable the system swap by executing `swapoff -a`, or this setting will be invalid after the machine is restarted.

To disable the system swap, execute the following command:
TiDB needs sufficient memory space for operation. When memory is insufficient, using swap as a buffer might degrade performance. Therefore, it is recommended to disable the system swap permanently by executing the following commands:

{{< copyable "shell-regular" >}}

Expand All @@ -127,6 +121,12 @@ swapoff -a && swapon -a
sysctl -p
```

> **Note:**
>
> - Executing `swapoff -a` and then `swapon -a` is to refresh swap by dumping data to memory and cleaning up swap. If you drop the swappiness change and execute only `swapoff -a`, swap will be enabled again after you restart the system.
>
> - `sysctl -p` is to make the configuration effective without restarting the system.

## Check and stop the firewall service of target machines

In TiDB clusters, the access ports between nodes must be open to ensure the transmission of information such as read and write requests and data heartbeats. In common online scenarios, the data interaction between the database and the application service and between the database nodes are all made within a secure network. Therefore, if there are no special security requirements, it is recommended to stop the firewall of the target machine. Otherwise, refer to [the port usage](/hardware-and-software-requirements.md#network-requirements) and add the needed port information to the allowlist of the firewall service.
Expand Down Expand Up @@ -191,17 +191,19 @@ To check whether the NTP service is installed and whether it synchronizes with t
- If it returns `Unit ntpd.service could not be found.`, then try the following command to see whether your system is configured to use `chronyd` instead of `ntpd` to perform clock synchronization with NTP:

{{< copyable "shell-regular" >}}

```bash
sudo systemctl status cronyd.service
sudo systemctl status chronyd.service
```

```
chronyd.service - NTP client/server
Loaded: loaded (/usr/lib/systemd/system/chronyd.service; enabled; vendor preset: enabled)
Active: active (running) since Mon 2021-04-05 09:55:29 EDT; 3 days ago
```


If the result shows that neither `chronyd` nor `ntpd` is configured, it means that neither of them is installed in your system. You should first install `chronyd` or `ntpd` and ensure that it can be automatically started. By default, `ntpd` is used.

If your system is configured to use `chronyd`, proceed to step 3.

2. Run the `ntpstat` command to check whether the NTP service synchronizes with the NTP server.
Expand Down