linux上进程打开句柄最大值是1024， 这只是默认情况而已：
ubuntu@VM-0-15-ubuntu:~$ ulimit -a
core file size (blocks, -c) 0
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 3306
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 1024
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 8192
cpu time (seconds, -t) unlimited
max user processes (-u) 3306
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited
ubuntu@VM-0-15-ubuntu:~$ 可见， 默认确实是1024, 此时， 无法做高并发服务器， 必须修改上限则行。
来看一个真实的在线跑的高并发服务器：
xxxxxx$ ulimit -a
core file size (blocks, -c) unlimited
data seg size (kbytes, -d) unlimited
scheduling priority (-e) 0
file size (blocks, -f) unlimited
pending signals (-i) 1027980
max locked memory (kbytes, -l) 64
max memory size (kbytes, -m) unlimited
open files (-n) 2000000
pipe size (512 bytes, -p) 8
POSIX message queues (bytes, -q) 819200
real-time priority (-r) 0
stack size (kbytes, -s) 8192
cpu time (seconds, -t) unlimited
max user processes (-u) 1027980
virtual memory (kbytes, -v) unlimited
file locks (-x) unlimited
上限是200万个， 足够了， epoll快来管理管理。