sysctl.conf 系统参数详解

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vim /etc/sysctl.conf

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#
# /etc/sysctl.conf - Configuration file for setting system variables
# See /etc/sysctl.d/ for additional system variables.
# See sysctl.conf (5) for information.
#

#kernel.domainname = example.com

# Uncomment the following to stop low-level messages on console
#kernel.printk = 3 4 1 3

##############################################################3
# Functions previously found in netbase
#

# Uncomment the next two lines to enable Spoof protection (reverse-path filter)
# Turn on Source Address Verification in all interfaces to
# prevent some spoofing attacks
#net.ipv4.conf.default.rp_filter=1
#net.ipv4.conf.all.rp_filter=1

# Uncomment the next line to enable TCP/IP SYN cookies
# See http://lwn.net/Articles/277146/
# Note: This may impact IPv6 TCP sessions too
#net.ipv4.tcp_syncookies=1

# Uncomment the next line to enable packet forwarding for IPv4
# 爽哥于2019.10.31修改,为了能搭建k8s
net.ipv4.ip_forward=1

# Uncomment the next line to enable packet forwarding for IPv6
#  Enabling this option disables Stateless Address Autoconfiguration
#  based on Router Advertisements for this host
#net.ipv6.conf.all.forwarding=1

###################################################################
# Additional settings - these settings can improve the network
# security of the host and prevent against some network attacks
# including spoofing attacks and man in the middle attacks through
# redirection. Some network environments, however, require that these
# settings are disabled so review and enable them as needed.
#
# Do not accept ICMP redirects (prevent MITM attacks)
#net.ipv4.conf.all.accept_redirects = 0
#net.ipv6.conf.all.accept_redirects = 0
# _or_
# Accept ICMP redirects only for gateways listed in our default
# gateway list (enabled by default)
# net.ipv4.conf.all.secure_redirects = 1
#
# Do not send ICMP redirects (we are not a router)
#net.ipv4.conf.all.send_redirects = 0
#
# Do not accept IP source route packets (we are not a router)
#net.ipv4.conf.all.accept_source_route = 0
#net.ipv6.conf.all.accept_source_route = 0
#
# Log Martian Packets
#net.ipv4.conf.all.log_martians = 1
#
kernel.sysrq = 1
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
kernel.printk = 5

https://blog.csdn.net/weixin_40901788/article/details/83586965

Wireshark抓包手机

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https://www.baidu.com/s?tn=50000021_hao_pg&ie=utf-8&sc=UWd1pgw-pA7EnHc1FMfqnHmzPW6Ln1fsn1n3rauW5y99U1Dznzu9m1Ydn1fzP1c4P1T&ssl_sample=normal&srcqid=5482817894475453453&H123Tmp=nunew7&word=wireshark%E6%80%8E%E4%B9%88%E6%8A%93%E5%8C%85%E6%89%8B%E6%9C%BA

https://www.google.com/search?q=mac+wireshark%E6%80%8E%E4%B9%88%E6%8A%93%E5%8C%85%E6%89%8B%E6%9C%BA&oq=mac+wireshark%E6%80%8E%E4%B9%88%E6%8A%93%E5%8C%85%E6%89%8B%E6%9C%BA&aqs=chrome..69i57.192j0j1&sourceid=chrome&ie=UTF-8

https://www.jianshu.com/p/82bcdb1decf7

MySQL中的WAL(Write-Ahead-Logging)

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数据库IO简介

IO有四种类型：连续读，随机读，随机写和连续写，连续读写的IO size通常比较大(128KB-1MB)，主要衡量吞吐量，而随机读写的IO size比较小(小于8KB)，主要衡量IOPS和响应时间。数据库中的全表扫描是连续读IO，索引访问则是典型的随机读IO，日志文件是连续写IO，而数据文件则是随机写IO。

　　数据库系统基于传统磁盘访问特性来设计，最大特点是日志文件采用sequential logging，数据库中的日志文件，要求必须在事务提交时写入到磁盘，对响应时间的要求很高，所以设计为顺序写入的方式，可以有效降低磁盘寻道花费的时间，减少延迟时间。日志文件的顺序写入，虽然是物理位置是连续的，但是并不同于传统的连续写类型，日志文件的IO size很小(通常小于4K),每个IO之间是独立的(磁头必须抬起来重新寻道，并等待磁盘转动到相应的位置)，而且间隔很短，数据库通过log buffer(缓存)和group commit的方式(批量提交)来达到提高IO size的大小，并减少IO的次数，从而得到更小的响应延迟，所以日志文件的顺序写入可以被认为是“连续位置的随机写入”，更关注IOPS，而不是吞吐量。

SpringBoot中使用Filter

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某个SpringBoot项目，在application.yml中指定了context-path：

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server:
  port: 8998
  servlet:
    context-path: /shuang-api/

这样一来，该项目所有的接口，根访问路径就都成了 ip:prot/shuang-api

service xxx start的使用

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https://www.baidu.com/s?ie=utf-8&f=8&rsv_bp=1&srcqid=7372498957567474605&tn=50000021_hao_pg&wd=service%20%20start%20%E5%A6%82%E4%BD%95%E5%B7%A5%E4%BD%9C%E7%9A%84&oq=service%2520xxx%2520start&rsv_pq=a3a465cb00051c79&rsv_t=0200YI4Jcg6vohyCpl6Fa%2Fp%2Frdpz1AP9ztBiquFlpvk%2B8Z1XpUaBu%2Fqs5QEi2dNpUcBNPYsq&rqlang=cn&rsv_enter=1&rsv_dl=tb&rsv_btype=t&inputT=8294&rsv_sug3=36&rsv_sug1=15&rsv_sug7=100&rsv_sug2=0&rsv_sug4=8979

https://blog.csdn.net/qq_38350635/article/details/114450408

https://blog.csdn.net/u011095110/article/details/81020839/

math/rand包源码剖析

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关于伪随机数生成算法

伪随机数生成器（pseudo random number generator，PRNG），又被称为确定性随机比特生成器（deterministic random bit generator，DRBG），是一个生成数字序列的算法，其特性近似于随机数序列的特性。PRNG生成的序列并不是真随机，因此它完全由一个初始值决定，这个初始值被称为PRNG的随机种子（seed，但这个种子可能包含真随机数）。尽管接近于真随机的序列可以通过硬件随机数生成器生成，但伪随机数生成器因为其生成速度和可再现的优势，在实践中也很重要