fotock

# 生成 dhparam.pem 文件, 在命令行执行任一方法:

# 方法1: 很慢
openssl dhparam -out /etc/nginx/ssl/dhparam.pem 2048

# 方法2: 较快
# 与方法1无明显区别. 2048位也足够用, 4096更强
openssl dhparam -dsaparam -out /etc/nginx/ssl/dhparam.pem 4096

understeer

Latency Comparison Numbers
--------------------------
L1 cache reference/hit                       1.5 ns                      4 cycles
Floating-point add/mult/FMA operation        1.5 ns                      4 cycles
L2 cache reference/hit                       5   ns                      12 ~ 17 cycles
Branch mispredict                            6   ns                      15 ~ 20 cycles
L3 cache hit (unshared cache line)          16   ns                      42 cycles
L3 cache hit (shared line in another core)  25   ns                      65 cycles
Mutex lock/unlock                           25   ns
L3 cache hit (modified in another core)     29   ns                      75 cycles

lenciel

Often referred to as the "swiss army of knife" for TCP/IP networking, [Netcat][1] is an extremely versatile Linux utility that allows you to do anything under the sun using TCP/UDP sockets. It is one of the most favorite tools for system admins when they need to do networking related troubleshooting and experimentation.

In this tutorial, I am sharing a few useful netcat examples, although the sky is the limit when it comes to possible netcat use cases. If you are using netcat regularly, feel free to share your use case.

Note that when you are binding to well-known ports (0-1023) with nc, you need root privilege. Otherwise, run nc as a normal user.

1. Test if a particular TCP port of a remote host is open.

$ nc -vn 192.168.233.208 5000