Cannot get "ISRG Root X1" chain certificates

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1

I tried to generate a "ISRG Root X1" certificate chain using command:

certbot certonly --manual --config-dir ./etc --logs-dir ./log --work-dir ./ --csr prime256v1.csr --preferred-chain 'ISRG Root X1' -d '*.ttc.icu' -m '1286196668@qq.com' --agree-tos --no-eff-email

since "DST Root CA X3" has already been expired and safari will show the following certificate expiration error:

Screen Shot 2021-11-23 at 9.12.17 PM
Screen Shot 2021-11-23 at 9.12.17 PM1362×726 108 KB

So, how can I create a 'ISRG Root X1' chain certificate and why the R3 is also expired according to safari? If it is expired, why it's keeping signing new certificates?

2

Check that your website configuration is using fullchain.pem not chain.pem otherwise the client operating system will try to resolve the R3 > ISRG Root X1 etc itself and in many case (macOS etc) that will fail.

3

Thank you! So, is there any case when we should only cert.pem instead of full chain?

4

Only in some old systems, where they require the cert to be provided in three parts:
cert.pem
chain.pem
privkey.pem

fullchain.pem = cert.pem + chain.pem