Avoid password prompt for keys and prompts for DN information

Edit: This is by far my most popular answer, and it's been a few years on now so I've added an ECDSA variant. If you can use ECDSA you should.

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You can supply all of that information on the command line.

One step self-signed password-less certificate generation:

RSA Version

openssl req \
    -new \
    -newkey rsa:4096 \
    -days 365 \
    -nodes \
    -x509 \
    -subj "/C=US/ST=Denial/L=Springfield/O=Dis/CN=www.example.com" \
    -keyout www.example.com.key \
    -out www.example.com.cert

ECDSA version

openssl req \
    -new \
    -newkey ec \
    -pkeyopt ec_paramgen_curve:prime256v1 \
    -days 365 \
    -nodes \
    -x509 \
    -subj "/C=US/ST=Denial/L=Springfield/O=Dis/CN=www.example.com" \
    -keyout www.example.com.key \
    -out www.example.com.cert

All of the openssl subcommands have their own man page. See man req.

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Specifically addressing your questions and to be more explicit about exactly which options are in effect:

1. The -nodes flag signals to not encrypt the key, thus you do not need a password. You could also use the -passout arg flag. See PASS PHRASE ARGUMENTS in the openssl(1) man page for how to format the arg.

2. Using the -subj flag you can specify the subject (example is above).

Doesn't -passin option do the trick for you?

With file:pathname form you can be quite safe with permissions 600 for that file.

The accepted answer needs a couple of small corrections. EC Lines:

-newkey ec
-pkeyopt ec_paramgen_curve:prime256v1

should be:

 -newkey ec \
 -pkeyopt ec_paramgen_curve:prime256v1 \

On MacOS - OpenSSL 1.0.2f installed via brew I verified the the accepted answer as described below

• To list available Elliptic curves:

  $ openssl ecparam -list_curves
  

• To generate a key file:

  $ openssl ecparam -name secp256k1 -out secp256k1.pem
  

• To generate the cert without password prompt:

  openssl req \
      -new \
      -newkey ec:secp256k1.pem \
      -days 365 \
      -nodes \
      -x509 \
      -subj "/C=US/ST=FL/L=Ocala/O=Home/CN=example.com" \
      -keyout server.key \
      -out server.crt
  

• To view the cert:

  $ openssl x509 -noout -text -in server.crt