the way of generating unique id uuid 128bit random too long snowflake 62bit increasing trend mysql auto_increatement strongly depond on db the problem of snowflake clock back 1. can’t guaratted to always bigger than enver

What is DNS, How it Works + Vulnerabilities https://www.cloudflare.com/learning/dns/what-is-dns/ what is DNS? GetIPWith(domain) how dns work? DNS recursive resolver(本地，递归):负责实际的查询过程: 运营商(电信，联通)，某些云服务商(谷歌) 查询过程: 按照层级，自高向低查询(域名自右向左)； root nameserver(根域名服务器,指向顶级域名) top level nameserver(顶级域名服务器 cn,com…) authoritative nameserver(权威域名服务器,存储实际 ip): 域名解析商，腾讯，阿里 DNS message format; command dig answer section: the actual IP AUTHORITY SECTION: the authoritative name server DNS recorder A: hostname and its corresponding ip4 address cname: alias a hostname to another hostname

basic Open Go 100 Days Code backslash 1 for shell command, (newline) represent a same line vairables with curly brackets variable expansion ${} distinguish it from other string: echo “${foo}name” excute some script: get array ${array[1]} replace variables: ${var/de/12}; curly braces $(): command expansion text transform awk vs sed: text process differ: sed: awk: more powerful awk print match 1 awk /rpc/ a.txt print some colume 1 2 3 4 5 6 7 8 data.

Filesystem Hierarchy Standard What is the difference between Unix, Linux, BSD and GNU? Linux Boot Process The BIOS/MBR Boot Process Master boot record 科普贴：BIOS和UEFI的启动项 linux architecture cpu,ram,disk, device, network; 1. the process of booting legacy feature: 不知道分区和文件，只能固定读取启动盘的第一个扇区； stage stage 1: 通过table 知道分区 stage 2: 通过引导程序 知道文件系统；； BIOS: basic input outpt system check haredware:Power On Self Test (post) load and excute bootloader in MRB following the boot sequeuce mbr/GPT: master boot recorder,stage 1

what is escape character invoke an alternative interpretation on the following characters; represent a special meaning which cannot be directly represented by alphabet; \n; 1 2 3 \t: tab; \n: move the cursor down to the newx line without return to the beegining(in unix, \n move to the beginning of the line) \r: carriage return(move the cursor to the beginning of the line without advacing to the next line) window: \r\n unix: \n

What is a TLS handshake? 面试官求你了，别再问我HTTPS 1. what is https https is a extension of http, and a secure http. 2. certificatin contents: The domain name that the certificate was issued for Which person, organization, or device it was issued to Which certificate authority issued it The certificate authority’s digital signature Associated subdomains Issue date of the certificate Expiration date of the certificate The public key (the private key is kept secret) 2.