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[转]在Linux下如何创建ramdisk

wythern — Wed, 26 Feb 2020 07:17:00 GMT

Refer to How to Easily Create Ramdisk on Linux

This tutorial will show you how to quickly create a RAM disk in any Linux distro (Debian, Ubuntu, Linux, Fedora, Arch Linux, CentOS, etc). Compared to commercial Windows RAM disk software that costs money, Linux can utilize this cool feature 100% free of charge.

What is RAM Disk?

RAM disk is also known as RAM drive. It’s a portion of your RAM that are formated with a file system. You can mount it to a directory on your Linux system and use it as a disk partition.

Why use RAM disk?

RAM is ultra-fast compared to even the fastest solid state drive (SSD). As you may know, the main performance bottleneck in today’s computer is the speed of hard drive, so moving programs and files to the RAM disk yields super fast computing experience.

Pros of RAM disk:

Ultra-fast
Can sustain countless reads and writes

Cons of RAM disk:

RAM is volatile which means all data in RAM disk will be lost when the computer shutdowns or reboots. However, this can be a pro in some situations, if you use it wisely.
RAM is expensive so it has limited capacity. You need to make sure not allocate too much space for RAM disk, or the operating system would run out of RAM.

You can do a lot of interesting things with RAM disk.

RAM disk is best suited for temporary data or caching directories, such as Nginx FastCGI cache. If you use a SSD and there will be a lot of writes to a particular directory, you can mount that directory as a RAM disk to reduce wear out of SSD.
I also use RAM disk to temporary store screenshots when writing articles on this blog, so when my computer shut down, those screenshots will automatically be deleted on my computer.
You may not believe it, but I use RAM disk to run virtual machines inside VirtualBox. My SSD is about 250G. I can’t run many VMs directly on the SSD and I’m not happy about the speed of my 2TB mechanical hard drive (HDD). I can move the VM from HDD to RAM disk before starting the VM, so the VM can run much faster. After shutting down the VM, I move the VM files back to HDD, which takes less than 1 minute. This of course requires your computer to have a large capacity RAM.

How to Create a RAM Disk in Any Linux Distro

First make a directory which can be anywhere in the file system such as

sudo mkdir /tmp/ramdisk

If you want to let every user on your Linux system use the RAM disk, then change its permission to 777.

sudo chmod 777 /tmp/ramdisk

Next, check how much free RAM are left on your system with htop command line utility because we don’t want to use too much RAM.

htop

Then all left to do is to specify the file system type, RAM disk size, device name and mount it to the above directory. You can see from the screenshot above that I have plenty of free RAM, so I can easily allocate 1GB for my RAM disk. This can be done with the following one-liner. It will be using tmpfs file system and its size is set to 1024MB. myramdisk is the device name I gave to it.

sudo mount -t tmpfs -o size=1024m myramdisk /tmp/ramdisk

To allocate 10G for the RAM disk, run this instead.

sudo mount -t tmpfs -o size=10G myramdisk /tmp/ramdisk

If we issue the following command

mount | tail -n 1

We can see it’s successfully mounted.

Now if I copy my VirtualBox machines file (5.8G) into the RAM disk, my RAM usage suddenly goes up to 9.22G.

If I unmount RAM disk,

sudo umount /tmp/ramdisk/

Everything in that directory will be lost and RAM usage goes down to original.

This is how you can test if your RAM disk is working.

Test RAM Disk Speed

To test write speed of RAM disk, you can use dd utility.

sudo dd if=/dev/zero of=/tmp/ramdisk/zero bs=4k count=100000

Which gave me 2.8GB/s write speed.

To test read speed, run:

sudo dd if=/tmp/ramdisk/zero of=/dev/null bs=4k count=100000

Which gave me 3.1 GB/s read speed.

I also did a speed test on my SSD. The write speed is 534MB/s and read speed 1.6GB/s.

Auto-mount on System Boot

Edit /etc/fstab file.

sudo nano /etc/fstab

Add an entry like this:

myramdisk  /tmp/ramdisk  tmpfs  defaults,size=1G,x-gvfs-show  0  0

x-gvfs-show will let you see your RAM disk in file manager. Save and close the file. Your Linux system will automatically mount the RAM disk when your computer boots up.

To mount it immediately without reboot, run the following command.

sudo mount -a

wythern 2020-02-26 15:17 发表评论

wythern — Thu, 28 Nov 2019 10:13:00 GMT

1. 使用pure或者view函数�Q�直接拿到返回��|��但不是所有的函数都能声明成pure/view�?/p>

2. 使用event包装�q�回��|��但是在emit之前�q�回的函数是没有event的，如果需要每条path都返回有意义的return value�Q�可能需要定义很多个event。（不考虑require throw的情况下�Q?/p>

3. 使用web3.eth.Contract.call�Q�需要ABI和deployed address�Q�这个用法有个缺�Ҏ��函数变成了constant的，卛_��1一��h��法改变合�U�内部状态，只能说在特定的场景下有用�?/p>

4. EIP-758(https://eips.ethereum.org/EIPS/eip-758)�Q�返回returnData在subscribe的通道上，但是看目前的状态还是draft�?/p>

wythern 2019-11-28 18:13 发表评论

[转]CRLF和LF在跨�q�_��工作时候带来的烦恼以及解决�Ҏ��

wythern — Wed, 27 Mar 2019 05:29:00 GMT

原文在此

在��用git提交代码时候，有时候会遇到一个问题，��是自己明明只修改了其中几行�Q�提交上��M��后发现整个文仉��被修改了�Q�在讄��了格式风��g��后还会有提交不上�ȝ��情况�Q�这个时候经常让人摸不到头脑�Q�其实就是CRLF和LF在作�?/p>

CRLF LF CR 都是什么意思：

CRLF: 是carriagereturnlinefeed的羃写。中文意思是回�R换行�?/p>
LF: 是line feed的羃写，中文意思是换行�?/p>
CR: 是carriagereturn的羃写。中文意思是回�R�?/p>

��单的换行回�R��Z��么会引出�q�么多的问题呢，关键在于操作�pȝ��之间的分歧：

早期的mac�pȝ��使用CR当做换行�Q�现在也已经�l�一成了LF

Unix(包含现在大量使用的linux)�pȝ��使用LF

windows�pȝ��使用LFCR当做换行�Q�自作聪明的兼容性？�Q�）

也正是因��Z��同系�l�的分歧�Q�在多�h协作共同开发的时候，可能��D��提交代码时候��生问题�?/p>

解决�Ҏ��Q?/h2>
Android Studio内部可以讄��不同模式�Q�具体位�|�在setting-->搜烦code style见下图：

讄��格式

其中有四个选项System-Dependent LF CR CRLF�Q�默认是System-Dependent�Q�也��是�Ҏ��你是什么系�l�选择什么类型，如果惌��自定义的话可以在�q�里讄��Q�以后创建的��C��码也默认用设�|�的方式

而如果想单独修改某个文�g的类型，也可以在右下角进行修改，见下图：

单独修改某个文�g

跨��^台合作时候的解决方式�Q?/h2>
当我们��用git库提交代码的时候，有的人可能��用mac�Q�有的�h使用linux�Q�有的�h使用windows�Q�不同的开发环境如果都是按照自��q��l�的方式��L��修改换行�c�d��Q�难免会让代码库整体混�ؕ或者��生许多没有必要的代码更新

那么解决该问题的方式有：core.autocrlf命��o

git��Z��防止以上问题��Cؕ跨��^台合作开发，使用命��o可以转化LF和CRLF

具体体现为：

git config --global core.autocrlf true

Git可以在你push时自动地把行�l�束�W�CRLF转换成LF�Q�而在pull代码时把LF转换成CRLF。用core.autocrlf来打开此项功能�Q�如果是在Windows�pȝ��上，把它讄��成true�Q�这样当�{�և�代码�Ӟ��LF会被转换成CRLF

git config --global core.autocrlf input

Linux或Mac�pȝ��使用LF作�ؓ行结束符�Q�当一个以CRLF��l�束�W�的文�g不小心被引入时你肯定惌��行修正，把core.autocrlf讄��成input来告�?Git 在push时把CRLF转换成LF�Q�pull时不转换

git config --global core.autocrlf false

在本地和代码库中都保留CRLF�Q�无论pull�q�是push都不变，代码库什么样�Q�本地还是什么样�?/p>
当然在多��q�_��工作时候，最好还是约定��用LF�Q�还是CRLF�Q�然后不同系�l�进行对应的讄��Q�这��h��工作规范�Q�也有利于提高工作效率，希望以上可以帮助大家�?/strong>

作者：sososun
链接�Q�https://www.jianshu.com/p/dd7464cf32b5
来源�Q�简�?br />��书著作权归作者所有，��M��形式的�{载都误��p�M��者获得授权�ƈ注明出处�?/div>

wythern 2019-03-27 13:29 发表评论

How to shuffle arrays and slices in Go

wythern — Thu, 17 Jan 2019 12:27:00 GMT
原文在此

�׃��Go没有为slice提供shuffle函数�Q�所以需要自己想办法。由于我只需要随��Z��ơ遍�? -> N�Q�所以这�D�code最匚w��?br />
func main() {
  vals := []int{10, 12, 14, 16, 18, 20}
  r := rand.New(rand.NewSource(time.Now().Unix()))
  for _, i := range r.Perm(len(vals)) {
    val := vals[i]
    fmt.Println(val)
  }
}

��g��go不像scala有那�U�惰性求值的�Ҏ��，所以这里的r.Perm()�q�是产生了一个slice�Q�如果N很大可能是个问题�?br />

wythern 2019-01-17 20:27 发表评论

wythern — Tue, 14 Aug 2018 09:04:00 GMT

��试中想通过命��o行传递一些参数给test func�Q�网上找了一些资料但�q�程不是很顺利，�q�里记录一下�?/div>

首先go test有一�?args的参数说可以辑ֈ��q�个目的�Q�但实测下来发现有没有没区别。。�?/div>
google查到的大部分也是用到了flag�c�d��?/div>
flag.go的注释写的比较清�?/div>

/*
    Package flag implements command-line flag parsing.

    Usage:

    Define flags using flag.String(), Bool(), Int(), etc.

    This declares an integer flag, -flagname, stored in the pointer ip, with type *int.
        import "flag"
        var ip = flag.Int("flagname", 1234, "help message for flagname")
    If you like, you can bind the flag to a variable using the Var() functions.
        var flagvar int
        func init() {
            flag.IntVar(&flagvar, "flagname", 1234, "help message for flagname")
        }
    Or you can create custom flags that satisfy the Value interface (with
    pointer receivers) and couple them to flag parsing by
        flag.Var(&flagVal, "name", "help message for flagname")
    For such flags, the default value is just the initial value of the variable.

    After all flags are defined, call
        flag.Parse()
    to parse the command line into the defined flags.

*/

因此需要做的事情就是：

1. 定义flag�Q�这个需要在main()执行之前完成�Q�我�q�里在test文�g里面用全局变量完成�Q�但a可以攑֜�函数里面�?/div>

var (
    // Define global args flags.
    pA = flag.Int("a", 0,  "a.")
    a = 0
)

2. parse flag�Q�这个要在test func执行之前�Q�所以可以考虑加入一个init()在test文�g里�?/div>

func init() {
    flag.Parse()
    a = *pA
}

后面使用�q�些变量��没有问题了�Q�比如这�?/div>

func TestInit(t *testing.T) {
    flag.Parse()
    t.Log("a = ", a)
}

�q�里用到的主要是flag的功能，��试用发现有没有-args问题不大�Q�所以这个用法可能不是很�W�合go test的要求，先用��h��再说了�?/div>

REF

1. https://www.golangtc.com/t/584cbd16b09ecc2e1800000b

2. https://stackoverflow.com/.../process-command-line-arguments-in-go-test
3. https://hsulei.com/2017/08/23/gotest如何使用自定义参�?

wythern 2018-08-14 17:04 发表评论

[转]shell中if条�g字符丌Ӏ�数字比对，[[ ]]和[ ]区别

wythern — Tue, 14 Aug 2018 08:44:00 GMT

原文在此
学习shell的时候��L��被shell里的条�g判断方式搞得头疼�Q�经�怸�知道�?用[],[[]],(())�q�是test,let�Q�而很��有书把它们的关�p�讲解的很清�?应该是我悟性差或是看书太少)�Q�今天�ȝ��一下，基础的东西如它们的��用方法不再赘�q�ͼ�重点说说它们的区别的使用时应该注意的地方�?br />
先说[]和test�Q�两者是一��L��Q�在命��o行里test expr和[ expr ]的效果相同。test的三个基本作用是判断文�g、判断字�W�串、判断整数。支持��用与或非��表辑ּ��q�接��h��。要注意的有�Q?br />
1.test中可用的比较�q�算�W�只�?=�?=�Q�两者都是用于字�W�串比较的，不可用于整数比较�Q�整数比较只能��?eq, -gt�q�种形式。无论是字符串比较还是整数比较都千万不要使用大于号小于号。当�Ӟ��如果你实在想用也是可以的�Q�对于字�W�串比较可以使用��括��L��转义形式�Q?如果比较"ab"�?bc"�Q�[ ab \< bc ]�Q�结果�ؓ真，也就是返回状态�ؓ0.

然后是[[ ]]�Q�这是内�|�在shell中的一个命令，它就比刚才说的test强大的多了。支持字�W�串的模式匹配（使用=~操作�W�时甚至支持shell的正则表�?式）。简直强大的令�h发指�Q�逻辑�l�合可以不��用test�?a,-o而��?amp;&,||�q�样更亲切的形式(针对c、Java�E�序�?。当 �Ӟ��也不用想的太复杂�Q�基本只要记�?br />1.字符串比较时可以把右边的作�ؓ一个模式（�q�是双��的字�W�串不加双引��L��情况下。如果右边的字符串加了双引号�Q�则认�ؓ是一个文本字�W�串。）�Q�而不仅仅是一个字�W�串�Q�比如[[ hello == hell? ]]�Q�结果�ؓ真�?/p>
另外要注意的是，使用[]和[[]]的时候不要吝啬空��|��每一��两辚w��要有�I�格�Q�[[ 1 == 2 ]]的结果�ؓ“�?#8221;�Q�但[[ 1==2 ]]的结果�ؓ“�?#8221;�Q�后一�U�显然是错的

3.最后就是let�?())�Q�两者也是一��L��(或者说基本上是一��L��Q�双括号比let�E�弱一�?。主要进行算术运��?上面的两个都不行)�Q�也比较适合�q?行整数比较，可以直接使用熟悉�?lt;,>�{�比较运��符。可以直接��用变量名如var而不需�?var�q�样的�Ş式。支持分号隔开的多个表辑ּ�

wythern 2018-08-14 16:44 发表评论

wythern — Wed, 01 Aug 2018 06:05:00 GMT

囄��来源�Q�https://blog.slock.it/public-vs-private-chain-7b7ca45044f

wythern 2018-08-01 14:05 发表评论

Full go tool list (keep constructing)

wythern — Sat, 21 Jul 2018 06:09:00 GMT
REF: https://dominik.honnef.co/posts/2014/12/an_incomplete_list_of_go_tools/

go get github.com/golang/lint/golint
go get github.com/kisielk/errcheck
go get golang.org/x/tools/cmd/benchcmp
go get github.com/cespare/prettybench
go get github.com/ajstarks/svgo/benchviz
go get golang.org/x/tools/cmd/stringer
go get github.com/josharian/impl
go get golang.org/x/tools/cmd/goimports
go get sourcegraph.com/sqs/goreturns
go get code.google.com/p/rog-go/exp/cmd/godef
go get github.com/nsf/gocode
go get golang.org/x/tools/cmd/oracle
go get golang.org/x/tools/cmd/gorename
go get github.com/kisielk/godepgraph

wythern 2018-07-21 14:09 发表评论

Some materials about RPC transaction call.

wythern — Sat, 14 Jul 2018 09:00:00 GMT

Introduction
Solidiay doc about ABI and contract access.

https://solidity.readthedocs.io/en/develop/abi-spec.html
https://solidity.readthedocs.io/en/latest/introduction-to-smart-contracts.html?highlight=selfdestruct
http://www.ethdocs.org/en/latest/contracts-and-transactions/accessing-contracts-and-transactions.html
http://ethdocs.org/en/latest/contracts-and-transactions/contracts.html#testing-contracts-and-transactions
https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=suicide [global variables like msg.sender]
ABI intro in Ethereum Wiki.
https://github.com/ethereum/wiki/wiki/Ethereum-Contract-ABI#argument-encoding
https://github.com/ethereum/go-ethereum/wiki/Contract-Tutorial
JAON rpc api of Eth.
https://github.com/ethereum/wiki/wiki/JSON-RPC#json-rpc-api
https://github.com/ethereum/wiki/wiki/JavaScript-API#contract-methods
Deploy a contract using RPC.
https://github.com/rsksmart/rskj/wiki/Deploying-contracts-using-RPC-calls
A tool to generate the grpc server code for a contract
https://github.com/getamis/grpc-contract

How to test.
http://ethereum-tests.readthedocs.io/en/latest/test_types/transaction_tests.html
https://github.com/ethereum/cpp-ethereum/blob/develop/doc/generating_tests.rst
go-ethereum里面有一批vm和contract相关的tests�Q�结合ABI和contract的定义，可以很容易的写一批自己定制的��试�Q�从web3js或者直接在go project里面调用都可以�?/div>

wythern 2018-07-14 17:00 发表评论

What is shade jar, and what is its purpose.

wythern — Mon, 19 Jun 2017 03:23:00 GMT

https://stackoverflow.com/questions/13620281/what-is-the-maven-shade-plugin-used-for-and-why-would-you-want-to-relocate-java

Uber JAR, in short, is a JAR containing everything.

Normally in Maven, we rely on dependency management. An artifact contains only the classes/resources of itself. Maven will be responsible to find out all artifacts (JARs etc) that the project depending on when the project is built.

An uber-jar is something that take all dependencies, and extract the content of the dependencies and put them with the classes/resources of the project itself, in one big JAR. By having such uber-jar, it is easy for execution, because you will need only one big JAR instead of tons of small JARs to run your app. It also ease distribution in some case.

Just a side-note. Avoid using uber-jar as Maven dependency, as it is ruining the dependency resolution feature of Maven. Normally we create uber-jar only for the final artifact for actual deployment or for manual distribution, but not for putting to Maven repository.

Update: I have just discovered I haven't answered one part of the question : "What's the point of renaming the packages of the dependencies?". Here is some brief updates and hopefully will help people having similar question.

Creating uber-jar for ease of deployment is one use case of shade plugin. There are also other common use cases which involve package renaming.

For example, I am developing Foo library, which depends on a specific version (e.g. 1.0) of Bar library. Assuming I cannot make use of other version of Bar lib (because API change, or other technical issues, etc). If I simply declare Bar:1.0 as Foo's dependency in Maven, it is possible to fall into a problem: A Qux project is depending on Foo, and also Bar:2.0 (and it cannot use Bar:1.0 because Qux needs to use new feature in Bar:2.0). Here is the dilemma: should Qux use Bar:1.0 (which Qux's code will not work) or Bar:2.0 (which Foo's code will not work)?

In order to solve this problem, developer of Foo can choose to use shade plugin to rename its usage of Bar, so that all classes in Bar:1.0 jar are embedded in Foo jar, and the package of the embedded Bar classes is changed from com.bar to com.foo.bar. By doing so, Qux can safely depends on Bar:2.0 because now Foo is no longer depending on Bar, and it is using is own copy of "altered" Bar located in another package.

wythern 2017-06-19 11:23 发表评论