这个帖子是一些使用Linux（Based on Debian）时的小技巧集合，不定期更新。有些内容可能其他Linux Distro也可以用。
裸机安装相关
移除不使用的kernel
查看当前kernel
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uname -a
以下是一个示例
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root@debian:~# uname -a Linux debian 6.1.0-10-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.1.37-1 (2023-07-03) x86_64 GNU/Linux
可以发现目前正在使用的时6.1.37-1的kernel，随后查看所有的kernel
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dpkg --list | grep linux-image
以下是一个示例
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root@debian:~# dpkg --list | grep linux-image rc linux-image-5.10.0-23-amd64 5.10.179-1 amd64 Linux 5.10 for 64-bit PCs (signed) ii linux-image-5.10.0-8-amd64 5.10.46-5 amd64 Linux 5.10 for 64-bit PCs (signed) ii linux-image-6.1.0-10-amd64 6.1.37-1 amd64 Linux 6.1 for 64-bit PCs (signed) ii linux-image-amd64 6.1.37-1 amd64 Linux for 64-bit PCs (meta-package)
root@debian:~# apt remove linux-image-5.10.0* Reading package lists... Done Building dependency tree... Done Reading state information... Done Note, selecting 'linux-image-5.10.0-23-amd64' for glob 'linux-image-5.10.0*' Note, selecting 'linux-image-5.10.0-8-amd64-unsigned' for glob 'linux-image-5.10.0*' Note, selecting 'linux-image-5.10.0-8-amd64' for glob 'linux-image-5.10.0*' Note, selecting 'linux-image-5.10.0-23-amd64-unsigned' for glob 'linux-image-5.10.0*' Package 'linux-image-5.10.0-23-amd64-unsigned' is not installed, so not removed Package 'linux-image-5.10.0-8-amd64-unsigned' is not installed, so not removed Package 'linux-image-5.10.0-23-amd64' is not installed, so not removed The following packages will be REMOVED: linux-image-5.10.0-8-amd64 0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded. After this operation, 302 MB disk space will be freed. Do you want to continue? [Y/n] y (Reading database ... 36690 files and directories currently installed.) Removing linux-image-5.10.0-8-amd64 (5.10.46-5) ... I: /vmlinuz.old is now a symlink to boot/vmlinuz-6.1.0-10-amd64 I: /initrd.img.old is now a symlink to boot/initrd.img-6.1.0-10-amd64 /etc/kernel/postrm.d/initramfs-tools: update-initramfs: Deleting /boot/initrd.img-5.10.0-8-amd64 /etc/kernel/postrm.d/zz-update-grub: Generating grub configuration file ... Found linux image: /boot/vmlinuz-6.1.0-10-amd64 Found initrd image: /boot/initrd.img-6.1.0-10-amd64 Warning: os-prober will not be executed to detect other bootable partitions. Systems on them will not be added to the GRUB boot configuration. Check GRUB_DISABLE_OS_PROBER documentation entry. done
funcdoSomething(time int) { println("Do something ", time, " time") }
funcfinishDoSomething(time int) { println("Finish do something ", time, " time") }
此时程序的输出为
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Do something 1 time Something has been done 1 time Star Over Do something 2 time Something has been done 2 time Finish do something 2 time Finish do something 1 time
前五行看下来似乎都没什么问题，着重看最后两行，为什么runningTimes变成2之后仍旧打出了 Finish do something 1 time呢? 这里其实与goto没有任何关系，是defer的特性，当程序经过defer时，会进行参数预计算，也就是说，当runTimes是1时，加载到defer finishDoSomething(runningTimes)的时候，就会把finishDoSomething(1)丢到栈里，所以最后可以打印出来Finish do something 1 time。 然后是打印次序及顺序的问题，把刚刚的执行过程用代码重新梳理一下可能就会好理解地多：
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doSomething(1) defer finishDoSomething(1) println("Something has been done ", 1, " time") println("Star Over") doSomething(2) defer finishDoSomething(2) println("Something has been done ", 2, " time")
funcdoSomething(time int) { println("Do something ", time, " time") }
funcfinishDoSomething(time int) { println("Finish do something ", time, " time") }
于是梅开二度：
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Do something 1 time Something has been done 1 time Star Over Do something 2 time Something has been done 2 time Finish do something 2 time Finish do something 2 time fatal error: sync: unlock of unlocked mutex
]]>Here's something encrypted, password is required to continue reading.记一次FLV直播流服务器搭建https://blog.archetto.moe/2022/03/24/Linux/Flv-Over-HTTP/2022-03-24T20:55:00.000Z2024-11-08T09:46:39.639Z
问题描述
为了压测公司开发的某视频服务，需要配置一个后端推流服务，以flv over http的方式进行推送，可能要承载一千个连接（512码率的视频）。
步骤
安装ffmpeg
默认给我的机子是Cent OS 7.6，系统有点陈旧，内核也有点老，一开始想直接升级成Cent OS 8，但是换了个5.x的内核导致一些依赖出错，索性直接一键DD成Debian 10（运维那边也没有现成的系统）。
deb http://mirrors.huaweicloud.com/debian buster main contrib non-free deb http://mirrors.huaweicloud.com/debian buster-updates main contrib non-free deb http://mirrors.huaweicloud.com/debian buster-backports main contrib non-free deb http://mirrors.huaweicloud.com/debian-security/ buster/updates main contrib non-free
# 直接下载最新的v4 beta 10 wget https://github.com/ossrs/srs/releases/download/v4.0-b10/srs-server-4.0-b10.tar.gz tar -zxvf srs-server-4.0-b10.tar.gz cd srs-4.0-b10/trunk && ./configure && make && make install
for key := range(set) { fmt.Println(key) } // each value will be printed only once, in no particular order
// you can use the ,ok idiom to check for existing keys if _, ok := set[1]; ok { fmt.Println("element found") } else { fmt.Println("element not found") }
其中使用空的struct可以规避空间分配，int可以替换为其他类型。
Slice是否相等比较
reflect方法
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funcStringSliceReflectEqual(a, b []string)bool { return reflect.DeepEqual(a, b) }
使用反射的方法进行对比，效率低下，但是代码简单
循环遍历进行比较
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funcStringSliceEqual(a, b []string)bool { iflen(a) != len(b) { returnfalse } if (a == nil) != (b == nil) { returnfalse } for i, v := range a { if v != b[i] { returnfalse } } returntrue }
BCE 优化版
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funcStringSliceEqualBCE(a, b []string)bool { iflen(a) != len(b) { returnfalse } if (a == nil) != (b == nil) { returnfalse } b = b[:len(a)] for i, v := range a { if v != b[i] { returnfalse } } returntrue }
func(m *Map) Store(key, value interface{}) { // 先不上锁，而是从只读数据中按key读取， 如果已存在以compareAndSwap操作进行覆盖(update) read, _ := m.read.Load().(readOnly) if e, ok := read.m[key]; ok && e.tryStore(&value) { return } m.mu.Lock() // 双检查获取read read, _ = m.read.Load().(readOnly) // 如果data在read中，更新entry if e, ok := read.m[key]; ok { // 如果原子操作读到的数据是被标记删除的， 则视为新数据写入dirty if e.unexpungeLocked() { m.dirty[key] = e } // 原子操作写新数据 e.storeLocked(&value) } elseif e, ok := m.dirty[key]; ok { // 原子操作写新数据 e.storeLocked(&value) } else { // 新数据 // 当dirty中没有新数据时，将read中数据冗余到dirty if !read.amended { m.dirtyLocked() m.read.Store(readOnly{m: read.m, amended: true}) } m.dirty[key] = newEntry(value) } m.mu.Unlock() }
func(e *entry) tryStore(i *interface{}) bool { p := atomic.LoadPointer(&e.p) if p == expunged { returnfalse } for { if atomic.CompareAndSwapPointer(&e.p, p, unsafe.Pointer(i)) { returntrue } p = atomic.LoadPointer(&e.p) if p == expunged { returnfalse } } }
func(m *Map) Delete(key interface{}) { read, _ := m.read.Load().(readOnly) e, ok := read.m[key] // 只读中不存在需要到dirty中去删除 if !ok && read.amended { m.mu.Lock() // 双检查， 因为上锁之前的语句是非原子性的 read, _ = m.read.Load().(readOnly) e, ok = read.m[key] if !ok && read.amended { delete(m.dirty, key) } m.mu.Unlock() } if ok { e.delete() } }
func(e *entry)delete() (hadValue bool) { for { p := atomic.LoadPointer(&e.p) if p == nil || p == expunged { returnfalse } if atomic.CompareAndSwapPointer(&e.p, p, nil) { returntrue } } }
funcrandomString(n int)string { b := make([]byte, n) for i := range b { b[i] = letterBytes[rand.Intn(len(letterBytes))] } returnstring(b) }
funcbenchmark(b *testing.B, f func(string, string)bool) { var str = "测试test" for i := 0; i < b.N; i++ { f(randomString(10)+str+randomString(10), str) } }
for key, value := range oldMap { newMap[key] = value }
很方便的切片
Switch
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funcunhex(c byte)byte { switch { case'0' <= c && c <= '9': return c - '0' case'a' <= c && c <= 'f': return c - 'a' + 10 case'A' <= c && c <= 'F': return c - 'A' + 10 } return0 }
// Hello returns a greeting for the named person. funcHello(name string) (string, error) { // If no name was given, return an error with a message. if name == "" { return"", errors.New("empty name") }
// If a name was received, return a value that embeds the name // in a greeting message. message := fmt.Sprintf("Hi, %v. Welcome!", name) return message, nil }
并发
协程
在函数或方法前添加 go 关键字能够在新的 Go 协程中调用它。当调用完成后， 该 Go 协程也会安静地退出。（效果有点像 Unix Shell 中的 & 符号，它能让命令在后台运行。）
(Name, Domain, NS, TTL) e.g. (Tinysnow, A NS Server, NS, TTL)
(Name, Domain, CNAME, TTL) e.g. (blog, skadiwo.github.io, CNAME, TTL)
(Name, Domain, MX, TTL) e.g. (mail, mail.163.com, MX, TTL) 禁止指向CNAME
报文构成
电子邮件系统的构成、传输机制和协议
构成与传输机制
于上图可知，因特网电子邮件系统有三个组成部分：用户代理(User Agent)、邮件服务器(Mail Server)、简单邮件传输协议(Simple Mail Transfer Protocol,SMTP) 一个典型的邮件发送过程是：从发送方的用户代理开始．传输到发送方的邮件服务器、再传输到接收方的邮件服务器，然后在这里被分发到接收方的邮箱中。
