To install offline, you need to download and SCP the RPM file into AirWave:
filename = dmidecode-2.12-5.el6_5.x86_64
((http://mirror.centos.org/centos/6/updates/x86_64/Packages/dmidecode-2.12-5.el6_5.x86_64.rpm))
transfer this into /var/airwave/custom
then install:
# rpm -i dmidecode-2.12-5.el6_5.x86_64
After that, you should be able to run the regular command:
# dmidecode -s system-serial-number