sudo strace -e trace=network -p `pidof nginx | sed -e 's/ /,/g'`

easily trace all Nginx processes

Nginx (and other webservers like Apache) can be awkward to trace. They run as root, then switch to another user once they're ready to serve web pages. They also have a "master" process and multiple worker processes. The given command finds the process IDs of all Nginx processes, joins them together with a comma, then traces all of them at once with "sudo strace." System trace output can be overwhelming, so we only capture "networking" output. TIP: to kill this complex strace, do "sudo killall strace". Compare with a similar command: http://www.commandlinefu.com/commands/view/11918/easily-strace-all-your-apache-processes
Sample Output
# grab an Nginx web page:
#     curl -so /dev/null localhost

[pid  1145] accept4(6, {sa_family=AF_INET, sin_port=htons(57358), sin_addr=inet_addr("127.0.0.1")}, [16], SOCK_NONBLOCK) = 10
[pid  1145] recvfrom(10, "GET / HTTP/1.1\r\nUser-Agent: curl"..., 1024, 0, NULL, NULL) = 73
[pid  1145] setsockopt(10, SOL_TCP, TCP_CORK, [1], 4) = 0
[pid  1145] sendfile(10, 11, [0], 612)  = 612
[pid  1145] setsockopt(10, SOL_TCP, TCP_CORK, [0], 4) = 0
[pid  1145] recvfrom(10, 0xa7e1c0, 1024, 0, 0, 0) = -1 EAGAIN (Resource temporarily unavailable)
[pid  1145] recvfrom(10, "", 1024, 0, NULL, NULL) = 0

1
2016-01-28 18:48:16

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