efu is one of the _d commands that can be use for debugging.efu is just working on LPUA.
Now you enter NE5000 diagnose command view .
[NE40E_26-diag-ne5000]efu interface GigabitEthernet 2/0/0 statistic ?
clear clear counter information
ipv4 NP counter information of IPV4
ipv6 NP counter information of IPV6
mc NP counter information of IPV4_MC
mpls NP counter information of MPLS
vlan NP counter information of VLAN
[NE40E_26-diag-ne5000]efu interface GigabitEthernet 2/0/0 statistic mpls
Target IO Board is not LPUA or GRE!
It showes me this warning because the remote interface is not LPUA or GRE. so it can not work here.
Both sides of a link should be LPUA or GRE board,if not efu interface command would not be working.