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
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鍦ㄤ嬌鐢╣it鎻愪氦浠ｇ爜鏃跺欙紝鏈夋椂鍊欎細(xì)閬囧埌涓涓棶棰橈紝灝辨槸鑷繁鏄庢槑鍙慨鏀逛簡(jiǎn)鍏朵腑鍑犺錛屾彁浜や笂鍘諱互鍚庡彂鐜版暣涓枃浠墮兘琚慨鏀逛簡(jiǎn)錛屽湪璁劇疆浜?jiǎn)鏍煎紡椋庢犻g互鍚庤繕?shù)細(xì)鏈夋彁浜や笉涓婂幦潥勬儏鍐靛Q岃繖涓椂鍊欑粡甯歌浜烘懜涓嶅埌澶磋剳錛屽叾瀹炲氨鏄疌RLF鍜孡F鍦ㄤ綔鎬?/p>
CRLF LF CR 閮芥槸浠涔堟剰鎬濓細(xì)
CRLF: 鏄痗arriagereturnlinefeed鐨勭緝鍐欍備腑鏂囨剰鎬濇槸鍥炶濺鎹㈣銆?/p>
LF: 鏄痩ine feed鐨勭緝鍐欙紝涓枃鎰忔濇槸鎹㈣銆?/p>
CR: 鏄痗arriagereturn鐨勭緝鍐欍備腑鏂囨剰鎬濇槸鍥炶濺銆?/p>
綆鍗曠殑鎹㈣鍥炶濺涓轟粈涔堜細(xì)寮曞嚭榪欎箞澶氱殑闂鍛紝鍏抽敭鍦ㄤ簬鎿嶄綔緋葷粺涔嬮棿鐨勫垎姝э細(xì)
鏃╂湡鐨刴ac緋葷粺浣跨敤CR褰撳仛鎹㈣錛岀幇鍦ㄤ篃宸茬粡緇熶竴鎴愪簡(jiǎn)LF
Unix(鍖呭惈鐜板湪澶ч噺浣跨敤鐨刲inux)緋葷粺浣跨敤LF
windows緋葷粺浣跨敤LFCR褰撳仛鎹㈣錛堣嚜浣滆仾鏄庣殑鍏煎鎬э紵錛燂級(jí)
涔熸鏄洜涓轟笉鍚岀郴緇熺殑鍒嗘錛屽湪澶氫漢鍗忎綔鍏卞悓寮鍙戠殑鏃跺欙紝鍙兘瀵艱嚧鎻愪氦浠ｇ爜鏃跺欎駭鐢熼棶棰樸?/p>
瑙ｅ喅鏂規(guī)硶錛?/h2>
Android Studio鍐呴儴鍙互璁劇疆涓嶅悓妯″紡錛屽叿浣撲綅緗湪setting-->鎼滅儲(chǔ)code style瑙佷笅鍥撅細(xì)
璁劇疆鏍煎紡
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鑰屽鏋滄兂鍗曠嫭淇敼鏌愪釜鏂囦歡鐨勭被鍨嬶紝涔熷彲浠ュ湪鍙充笅瑙掕繘琛屼慨鏀癸紝瑙佷笅鍥撅細(xì)
璺ㄥ鉤鍙板悎浣滄椂鍊欑殑瑙ｅ喅鏂瑰紡錛?/h2>
褰撴垜浠嬌鐢╣it搴撴彁浜や唬鐮佺殑鏃跺欙紝鏈夌殑浜哄彲鑳戒嬌鐢╩ac錛屾湁鐨勪漢浣跨敤linux錛屾湁鐨勪漢浣跨敤windows錛屼笉鍚岀殑寮鍙戠幆澧冨鏋滈兘鏄寜鐓ц嚜宸辯郴緇熺殑鏂瑰紡浠繪剰淇敼鎹㈣綾誨瀷錛岄毦鍏嶄細(xì)璁╀唬鐮佸簱鏁翠綋娣蜂貢鎴栬呬駭鐢熻澶氭病鏈夊繀瑕佺殑浠ｇ爜鏇存柊
閭ｄ箞瑙ｅ喅璇ラ棶棰樼殑鏂瑰紡鏈夛細(xì)core.autocrlf鍛戒護(hù)
git涓轟簡(jiǎn)闃叉浠ヤ笂闂鎵頒貢璺ㄥ鉤鍙板悎浣滃紑鍙戯紝浣跨敤鍛戒護(hù)鍙互杞寲LF鍜孋RLF
鍏蜂綋浣撶幇涓猴細(xì)
- git config --global core.autocrlf true
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- git config --global core.autocrlf input
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- git config --global core.autocrlf false
鍦ㄦ湰鍦板拰浠ｇ爜搴撲腑閮戒繚鐣機(jī)RLF錛屾棤璁簆ull榪樻槸push閮戒笉鍙橈紝浠ｇ爜搴撲粈涔堟牱錛屾湰鍦拌繕鏄粈涔堟牱瀛?/p>
褰撶劧鍦ㄥ浜鴻法騫沖彴宸ヤ綔鏃跺欙紝鏈濂借繕鏄害瀹氫嬌鐢↙F錛岃繕鏄疌RLF錛岀劧鍚庝笉鍚岀郴緇熻繘琛屽搴旂殑璁劇疆錛岃繖鏍鋒槸宸ヤ綔瑙勮寖錛屼篃鏈夊埄浜庢彁楂樺伐浣滄晥鐜囷紝甯屾湜浠ヤ笂鍙互甯姪澶у銆?/strong>
浣滆咃細(xì)sososun
閾炬帴錛歨ttps://www.jianshu.com/p/dd7464cf32b5
鏉ユ簮錛氱畝涔?br />綆涔﹁憲浣滄潈褰掍綔鑰呮墍鏈夛紝浠諱綍褰㈠紡鐨勮漿杞介兘璇瘋仈緋諱綔鑰呰幏寰楁巿鏉冨茍娉ㄦ槑鍑哄銆?/div>
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鐢變簬Go娌℃湁涓簊lice鎻愪緵shuffle鍑芥暟錛屾墍浠ラ渶瑕佽嚜宸辨兂鍔炴硶銆傜敱浜庢垜鍙渶瑕侀殢鏈轟竴嬈￠亶鍘? -> N錛屾墍浠ヨ繖孌礳ode鏈鍖歸厤銆?br />
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)
}
}
浼間箮go涓嶅儚scala鏈夐偅縐嶆儼鎬ф眰鍊肩殑鐗規(guī)э紝鎵浠ヨ繖閲岀殑r.Perm()榪樻槸浜х敓浜?jiǎn)涓涓猻lice錛屽鏋淣寰堝ぇ鍙兘鏄釜闂銆?br />
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3.鏈鍚庡氨鏄痩et鍜?())錛屼袱鑰呬篃鏄竴鏍風(fēng)殑(鎴栬呰鍩烘湰涓婃槸涓鏍風(fēng)殑錛屽弻鎷彿姣攍et紼嶅急涓浜?銆備富瑕佽繘琛岀畻鏈繍綆?涓婇潰鐨勪袱涓兘涓嶈)錛屼篃姣旇緝閫傚悎榪?琛屾暣鏁版瘮杈冿紝鍙互鐩存帴浣跨敤鐔熸?zhèn)夌?lt;,>絳夋瘮杈冭繍綆楃銆傚彲浠ョ洿鎺ヤ嬌鐢ㄥ彉閲忓悕濡倂ar鑰屼笉闇瑕?var榪欐牱鐨勫艦寮忋傛敮鎸佸垎鍙烽殧寮鐨勫涓〃杈懼紡
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Introduction
How to test.
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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.
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