openssl verify -verbose -purpose any
-CAfile /full/path/sub.domain.com-geotrust.crt  /full/path/sub.domain.com.crt

openssl x509 -text -in sub.domain.crt and
openssl x509 -text -in sub.domain-geotrust.crt (CA root file)

sub.domain.com
Subject:    OU=GT44865949,
            OU=See www.geotrust.com/resources/cps (c)15,
            OU=Domain Control Validated - QuickSSL(R),
            CN=sub.domain.com
Issuer:
            commonName                = GeoTrust DV SSL CA - G4
            organizationalUnitName    = Domain Validated SSL
            organizationName          = GeoTrust Inc.
            countryName               = US

Intermediate:
Subject:
            commonName                = GeoTrust DV SSL CA - G4
            organizationalUnitName    = Domain Validated SSL
            organizationName          = GeoTrust Inc.
            countryName               = US

Issuer:
            commonName                = GeoTrust Global CA
            organizationName          = GeoTrust Inc.
            countryName               = US

Root:
Subject:
            commonName                = GeoTrust Global CA
            organizationName          = GeoTrust Inc.
            countryName               = US
Issuer:
            organizationalUnitName    = Equifax Secure Certificate Authority
            organizationName          = Equifax
            countryName               = US