Question related to starting a systemd service after the network is online, even when DNS may not be available immediately. If you're facing a similar issue, here are some possible solutions:
1. **Wait for DNS Resolution in Your Service Script**:
Inside your systemd service unit, you can specify `ExecStartPre` to execute a script before your service starts. You can use this to check for DNS availability by trying to resolve a well-known domain name and waiting until it succeeds. Here's an example of what it could look like:
```ini
[Service]
ExecStartPre=/path/to/script.sh
ExecStart=/your/actual/service
```
In the `script.sh`, you can use a loop to check for DNS resolution:
```bash
#!/bin/bash
while ! host -t A google.com; do
sleep 1
done
```
2. **Use `After` and `Wants` Directives**:
You can adjust your systemd service unit by adding `After` and `Wants` directives to make your service depend on network-online.target but not directly on network.target. This can help ensure that your service starts after the network is online but doesn't necessarily require DNS to be fully functional:
```ini
[Unit]
Wants=network-online.target
After=network-online.target
```
3. **Custom Network Check**:
If the `network-online.target` does not suit your requirements, you can create a custom network check service and make your service depend on it. This custom service can incorporate more specific checks, including DNS resolution.
For example, you could create a custom service that runs a script similar to the one mentioned in option 1 to verify network availability.
4. **DNS Service Dependency**:
You can make your service depend explicitly on a DNS service. However, this approach assumes that you have a DNS service unit defined in your systemd setup. Here's an example of how your service unit might look:
```ini
[Unit]
After=network-online.target
Wants=network-online.target
After=dns.service
[Service]
ExecStart=/your/actual/service
```
The approach you choose may depend on your specific requirements and how your system is configured. Options 1 and 2 are more general approaches and should work on most systemd-based systems. Options 3 and 4 require more customization and may depend on the specifics of your environment.