One colleague, linux expert, pointed me to this : #1527902
he did some strace and find : 60735 gettimeofday({1463755505, 995830}, NULL) = 0 60735 sendmsg(20, {msg_name(28)={sa_family=AF_INET6, sin6_port=htons(53), inet_pton(AF_INET6, "2001:660:660c:120::226", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0}, msg_iov(1)=[{"\236\207\1 \ 0\1\0\0\0\0\0\1\3www\6google\2fr\0\0\1\0\1\0"..., 42}], msg_controllen=0, msg_flags=0}, 0) = 42 60735 futex(0x7f7ab325d0a4, FUTEX_WAIT_PRIVATE, 3, NULL <unfinished ...> 60737 <... epoll_wait resumed> [{EPOLLIN, {u32=3, u64=3}}], 64, -1) = 1 60737 read(3, "\24\0\0\0\375\377\377\377", 8) = 8 60737 epoll_ctl(5, EPOLL_CTL_ADD, 20, {EPOLLIN, {u32=20, u64=20}}) = 0 60737 read(3, 0x7f7aac706e40, 8) = -1 EAGAIN (Resource temporarily unavailable) 60737 epoll_wait(5, <unfinished ...> 60736 <... futex resumed> ) = -1 ETIMEDOUT (Connection timed out)
One colleague, linux expert, pointed me to this : #1527902
he did some strace and find : {1463755505, 995830}, NULL) = 0 28)={sa_ family= AF_INET6, sin6_port= htons(53) , inet_pton(AF_INET6, "2001:660: 660c:120: :226", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0}, msg_iov( 1)=[{"\ 236\207\ 1 \ 0\0\0\1\ 3www\6google\ 2fr\0\0\ 1\0\1\0" ..., 42}], msg_controllen=0, msg_flags=0}, 0) = 42 5d0a4, FUTEX_WAIT_PRIVATE, 3, NULL <unfinished ...> 0\0\375\ 377\377\ 377", 8) = 8
60735 gettimeofday(
60735 sendmsg(20, {msg_name(
0\1\0\0\
60735 futex(0x7f7ab32
60737 <... epoll_wait resumed> [{EPOLLIN, {u32=3, u64=3}}], 64, -1) = 1
60737 read(3, "\24\0\
60737 epoll_ctl(5, EPOLL_CTL_ADD, 20, {EPOLLIN, {u32=20, u64=20}}) = 0
60737 read(3, 0x7f7aac706e40, 8) = -1 EAGAIN (Resource temporarily unavailable)
60737 epoll_wait(5, <unfinished ...>
60736 <... futex resumed> ) = -1 ETIMEDOUT (Connection timed out)