How to find the socket buffer size of linux
If you want see your buffer size in terminal, you can take a look at:
/proc/sys/net/ipv4/tcp_rmem
(for read)/proc/sys/net/ipv4/tcp_wmem
(for write)
They contain three numbers, which are minimum, default and maximum memory size values (in byte), respectively.
Whilst, as has been pointed out, it is possible to see the current default socket buffer sizes in /proc
, it is also possible to check them using sysctl
(Note: Whilst the name includes ipv4 these sizes also apply to ipv6 sockets - the ipv6 tcp_v6_init_sock() code just calls the ipv4 tcp_init_sock() function):
sysctl net.ipv4.tcp_rmem
sysctl net.ipv4.tcp_wmem
However, the default socket buffers are just set when the sock is initialised but the kernel then dynamically sizes them (unless set using setsockopt() with SO_SNDBUF). The actual size of the buffers for currently open sockets may be inspected using the ss
command (part of the iproute
/iproute2
package), which can also provide a bunch more info on sockets like congestion control parameter etc. E.g. To list the currently open TCP (t
option) sockets and associated memory (m
) information:
ss -tm
Here's some example output:
State Recv-Q Send-Q Local Address:Port Peer Address:Port
ESTAB 0 0 192.168.56.102:ssh 192.168.56.1:56328
skmem:(r0,rb369280,t0,tb87040,f0,w0,o0,bl0,d0)
Here's a brief explanation of skmem (socket memory) - for more info you'll need to look at the kernel sources (i.e. sock.h):
r:sk_rmem_alloc rb:sk_rcvbuf # current receive buffer size t:sk_wmem_alloc tb:sk_sndbuf # current transmit buffer size f:sk_forward_alloc w:sk_wmem_queued # persistent transmit queue size o:sk_omem_alloc bl:sk_backlog d:sk_drops
For getting the buffer size in c/c++ program the following is the flow
int n;
unsigned int m = sizeof(n);
int fdsocket;
fdsocket = socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP); // example
getsockopt(fdsocket,SOL_SOCKET,SO_RCVBUF,(void *)&n, &m);
// now the variable n will have the socket size