Linux: dropped packet stats

ifconfig

 ... 
 RX packets:522 errors:0 dropped:0 overruns:0 frame:0
 TX packets:406 errors:0 dropped:0 overruns:0 frame:0
 ...

cat /proc/net/dev

Inter-| Receive ... 
 face | bytes packets errs drop fifo frame ... 
 eth0:  87689 785 0 0 0 0 ...
 ...

cat /proc/net/udp

 so local_address rem_address ... drops
 277: 00000000:0044 00000000:0000 ... 0 
 ...

cat /proc/net/snmp

...
Tcp: ...
Udp: InDatagrams NoPorts InErrors OutDatagrams RcvbufErrors SndbufErrors
Udp: 453 0 0 452 0 0
...

You can also see this on a per-process basis using:

cat /proc/<pid>/net/{udp,dev,snmp}