# yum -y install opendkim

# cp /etc/opendkim.conf /etc/opendkim.conf.orig
# id opendkim
uid=367(opendkim) gid=365(opendkim) groups=365(opendkim),12(mail)

# opendkim-genkey --help
opendkim-genkey: usage: opendkim-genkey [options]
	--append-domain        include domain name in zone file stub
	--bits=n               use n bits to generate the key
	--directory=path       leave output in the named directory
	--domain=name          generate data for the named domain [example.com]
	--hash-algorithms=list limit to use of the named algorithm(s)
	--help                 print help and exit
	--note=string          include specified note in zone data
	--restrict             restrict key to email use only
	--selector=name        selector name [default]
	--subdomains           allow signing of subdomains
	--testmode             indicate key is in test mode
	--verbose              increased output
	--version              print version and exit