-out filename
the output filename. If this argument is not specified then standard output is used.
-passout arg
the output file password source. For more information about the format of arg see the PASS PHRASE ARGUMENTS section in openssl(1).
-des|-des3|-idea
These options encrypt the private key with the DES, triple DES, or the IDEA ciphers respectively before outputting it. If none of these options is specified no encryption is used. If encryption is used a pass phrase is prompted for if it is not supplied via the -passout argument.
-F4|-3
the public exponent to use, either 65537 or 3. The default is 65537.
-rand file(s)
a file or files containing random data used to seed the random number generator, or an EGD socket (see RAND_egd(3)). Multiple files can be specified separated by a OS-dependent character. The separator is ; for MS-Windows, , for OpenVMS, and : for all others.
-engine id
specifying an engine (by its unique id string) will cause genrsa to attempt to obtain a functional reference to the specified engine, thus initialising it if needed. The engine will then be set as the default for all available algorithms.
numbits
the size of the private key to generate in bits. This must be the last option specified. The default is 512.