Difference between tcp recv buffer and tcp receive window size?

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http://serverfault.com – The command shows the tcp receive buffer size in bytes. $ cat /proc/sys/net/ipv4/tcp_rmem 4096 87380 4001344 where the three values signifies the min, default and max values respectively. Then I tried to find the tcp window size using tcpdump command. $ sudo tcpdump -n -i eth0 'tcp[tcpflags] & (tcp-syn|tcp-ack) == tcp-syn and port 80 and host google.com' tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes 16:15:41.465037 IP > Flags [S], se (HowTos)