Create a Remote Git Repository Server

I had covered my first adventures with Git in a previous post. That article focused on creating a local repository; you could save your versions to the local hard drive. That approach works well enough for local work...you can roll back changes, keep track of changes, get frustrated with Git on your local system.

But what if you want to have some redundancy in the case of hard disk failure? Or if you want to work on multiple machines?

In that case you might want to create a simple Git server, a system on which to save your progress and transfer them to other machines. The process isn't all that difficult.

In this example I'm going to turn a Raspberry Pi with a USB-connected hard drive into a network Git server.

Create the Git User on the Server

First, on the Pi, I add a git user.

sudo adduser git
su git
cd
mkdir .ssh
chmod 700 ./.ssh

Raspian on the Pi had an implementation of adduser that asked for the password by default. If yours didn't, you'd have to run "sudo passwd git" after creating the user so you can su into the account. Plus you generally want a password on any account you create on a networked machine...

Enable Passwordless Connection with SSH

Now I'm going to get a public key from the developer (client) machine.

If you have a .id_rsa.pub in your ~/.ssh directory, you're already set. If not, you can usually create one with a variation of:

ssh-keygen -t rsa -C "your_email@address.com"

Then transfer the public key to the git server. ONLY transfer the .pub file!

scp ~/.ssh/id_rsa.pub git@gitserveraddress:~/

Now, back on the Git server:

mv ~/id_rsa.pub /home/git/.ssh
cd /home/git/.ssh

Make sure the .pub file is owned by the git user. If there are no other files in .ssh (which there aren't, if this is the first time you're setting this up...just rename the .pub file to authorized_keys. If the file were already there, I'd append the new .pub file contents to authorized_keys. 

mv id_rsa.pub authorized_keys

Now, if you're on the client computer and run "ssh git@gitmachinesaddress, it should automatically log in.

Time to Create a Workspace to Save Projects

Next step is to create your git workspace. On the Pi, I'm going to put it into my USB-connected drive instead of the SSD card. If you're familiar with Linux, it's not hard to suss out what I'm doing and what you'll have to modify for your own installation. I'm going to exit back to my default user (who already has sudo ability, which git doesn't...) to do the following.

cd /mnt/mydrive
sudo mkdir gitrepo
sudo chown git:git gitrepo

Create a Directory For Your Project (Each Time)

Now create a directory, as git, for your project. In this case, I'm going to use my loopcheck.go test application. As git, create the loopcheck project directory.

su git
cd /mnt/mydrive/gitrepo
mkdir loopcheck.git
cd loopcheck.git
git --bare init

Push the Project to the Server

Almost there! On the development computer, add the remote repo and push it to the server. You did already have the project git-staged, yes?

From the project's source code directory (where you already have git versioning...)

git remote add origin git@gitserveraddress:/mnt/mydrive/gitrepo/loopcheck.git
git push origin master

There you go! Now the loopcheck project is on the local system and a remote git server!

Pull the Project to Another Client

If you want to duplicate your project on another system, you can use the clone command. Most Go projects live under /src. So I would connect to the system I want to work on and (for me) 

cd ./go/src
git clone git@gitserveraddress:/path/to/repo/on/server/loopcheck.git

...at that point I should have the loopcheck project available, and can cd into the project, edit files, and use 

git add .
git commit -m "message for the commit"
git push

...to update the repo! Be aware that if you didn't install the public key from the new workstation, it will prompt you for the git user's password in order to download the project.

There is no tracking information for the current branch...

When I tried pulling the changes from client 2 to client 1, I had an error that began, "There is no tracking information for the current branch..."

A quick fix is to use 

git branch --set-upstream-to=origin/master master

...then it let me use git pull to pull the changes.

Learning to Profile a Go Application (pprof Fun)

I had previously written about a mini-application I used to test modulo vs looping performance. I thought, in the spirit of learning more about programming practices, I should try my hand at profiling the application as well. Maybe it would give some insight in how to analyze application performance!

I'll get this out of the way first. Most of the steps I'll review here work on the Mac. Except the output is broken, as of Go version 1.4.2. According to what I found online, it's a kernel bug with Darwin, not a flaw in Go. So in my case, I'm not going to use Darwin to profile application performance.

I should probably note that this is probably for the best anyway; some of the output options really want dot, from graphviz, installed in order to work, and getting it installed on the Mac was a little bit of a pain.

Now on to profiling

After discovering this little glitch with the Mac, I copied the source code to a Raspberry Pi. That way it's running under a version of Linux, and if anything shows performance issues, it would probably be the poor little Pi's processor (even though there could be performance differences due to the processor architecture. I'm kind of hoping a bottleneck in simple code is a bottleneck no matter the platform...just mentioning this as a warning to consider.)

As I previously mentioned, some of pprof's output really loves using graphviz, so that was the first thing to install. On the Pi I just used apt to grab it from the repo.

sudo apt-get install graphviz

Now I focused on the Go code. I created the application's directory under src and copied the loopcheck file into it. Next, I pulled the profile package from Dave Cheney into my pkg list.

go get github.com/davecheney/profile

This has moved. Use this command...
go get github.com/pkg/profile

Then I insert some references in the source. In my import list, I included:

import(
     //current imports...
     "github.com/davecheney/profile"
     "github.com/pkg/profile"
)

and the first line in Main() was:

     // Profiling!
     defer profile.Start(profile.CPUProfile).Stop()

Last step in prepping the application:

go install

That's all there is to it for prepping your application to grab CPU profiles. I think "go build" would also work, but this outlines I how did it.

NEXT I discovered yet another oddity. The test runs were fast. Like, really really fast, compared to my bigger-horsepower Mac. I added a quick line of code to print out the numbers being randomly generated and discovered that the Mac was generating int64's for my test cases, while the pi was generating (and casting to int64) int32 numbers. 

Now, I knew the Mac was generating really big numbers. For my purposes I needed really big numbers to loop through, so it wasn't a big deal. But now I see that on the Pi, it's actually following the rules of expected behavior, which wasn't what I had come to expect.

See if you can make sense of that statement.

I asked about it on StackOverflow, and as I suspected, it was the processor that made the difference. Meh, not a problem. I edited the source to be explicit and "correct." The previous blog post is using the incorrect (unexpected) behavior, so I guess this one is more "correct." Now I was going to deal with 32 bit numbers case into a 64 bit type (again, to better align with what I was testing in the actual program this was a test case for...)

I ran the program, and it generated a profile in /tmp. I next copied it to my working directory.

cp /tmp/profile510472042/cpu.pprof ./cpu_10000_serial_verbose.pprof

The location of the profile was initially printed to the console when I ran the program, but I also knew it was in /tmp/profile*, so finding it wasn't difficult. The name I used for the local copy reflects how I ran the application so I knew the codepath execution took.

Final step is to generate some profile information. You can view the text right in the console:

go tool pprof --text loopcheck ./cpu_10000_serial_verbose.pprof

...or view it with with a non-graphical graphical mode.

go tool pprof --tree loopcheck ./cpu_10000_serial_verbose.pprof 

The output is at the "function" level. You can tell it to output information at the "line" level if you want to get a better idea where the CPU is spinning.

go tool pprof --tree -lines loopcheck ./cpu_10000_serial_verbose.pprof

And of course there's the awesome PDF output with a graphical view of CPU usage.

go tool pprof --pdf -lines loopcheck ./cpu_10000_serial_verbose.pprof > cpu_10000_serial_verbose.pdf

Maybe you want to track the memory usage. To do that I modified the line added to main():

        // Profiling!

        defer profile.Start(profile.MemProfile).Stop()

Recompile, re-run, and follow the above steps to copy the pprof file and run "go tool pprof...", only against the mem* file instead of cpu*. 

Happy analyzing!

Oh, if you're curious, here's the source code I was using for my test...

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package main import ( "fmt" "math/rand" "os" "strconv" "sync" "time" "github.com/davecheney/profile" ) var slcTimes []int64 var boolSilent bool func main() { // Profiling! defer profile.Start(profile.MemProfile).Stop() var intCounter int var strCounter string var strMode string var strChatty string if len(os.Args) < 4 { fmt.Println("Usage: ./loopcheck <count> <serial|parallel|modulo|massive> <verbose|silent>") os.Exit(1) } strCounter = os.Args[1] strMode = os.Args[2] strChatty = os.Args[3] intCounter, err := strconv.Atoi(strCounter) if err != nil { fmt.Println("This doesn't appear to be a valid count: " + strCounter) os.Exit(1) } if strMode != "serial" && strMode != "parallel" && strMode != "massive" && strMode != "modulo" { fmt.Println("Need a mode as second argument of serial, parallel, massive or modulo, not " + strMode) os.Exit(1) } switch strChatty { case "verbose": boolSilent = true case "silent": boolSilent = false default: fmt.Println("Please set verbose or silent run") os.Exit(1) } // Seed the Random function rand.Seed(time.Now().UTC().UnixNano()) var int64Random int64 // 604,800 seconds is a week... // Fill the slice with values for b := 0; b < intCounter; b++ { //int64Random = rand.Int63() int64Random = int64(rand.Int31()) slcTimes = append(slcTimes, int64Random) } if strMode == "serial" { for i := range slcTimes { HowMuchTime(i) } } if strMode == "massive" { var wg sync.WaitGroup wg.Add(len(slcTimes)) for i := range slcTimes { go HowMuchTimeMassive(&wg, i) } wg.Wait() } if strMode == "modulo" { for i := range slcTimes { // Set the integers intCenturies := 0 intDecades := 0 intYears := 0 intMonths := 0 intWeeks := 0 intDays := 0 intHours := 0 intMinutes := 0 // Let's get the time to deletion for each entry int64TimeInSeconds := slcTimes[i] // How many centuries? intCenturies = int(int64TimeInSeconds / 3155692600) int64TimeInSeconds = int64TimeInSeconds % 3155692600 // How many decades? intDecades = int(int64TimeInSeconds / 315569260) int64TimeInSeconds = int64TimeInSeconds % 315569260 // How many years? intYears = int(int64TimeInSeconds / 31556926) int64TimeInSeconds = int64TimeInSeconds % 31556926 // How many months? intMonths = int(int64TimeInSeconds / 2629743) int64TimeInSeconds = int64TimeInSeconds % 2629743 // How many weeks? intWeeks = int(int64TimeInSeconds / 604800) int64TimeInSeconds = int64TimeInSeconds % 604800 // How many days? intDays = int(int64TimeInSeconds / 86400) int64TimeInSeconds = int64TimeInSeconds % 86400 // How many hours? intHours = int(int64TimeInSeconds / 3600) int64TimeInSeconds = int64TimeInSeconds % 3600 // How many minutes? intMinutes = int(int64TimeInSeconds / 60) // Convert to strings strCenturies := strconv.Itoa(intCenturies) strDecades := strconv.Itoa(intDecades) strYears := strconv.Itoa(intYears) strMonths := strconv.Itoa(intMonths) strWeeks := strconv.Itoa(intWeeks) strDays := strconv.Itoa(intDays) strHours := strconv.Itoa(intHours) strMinutes := strconv.Itoa(intMinutes) // Formatting strCenturies = strCenturies + " Centuries " strDecades = strDecades + " Decades " strYears = strYears + " Years " strMonths = strMonths + " Months " strWeeks = strWeeks + " Weeks " strDays = strDays + " Days " strHours = strHours + " Hours " strMinutes = strMinutes + " Minutes " strMessages := "From " + strconv.FormatInt(slcTimes[i], 10) + " : " + strCenturies + strDecades + strYears + strMonths + strWeeks + strDays + strHours + strMinutes if boolSilent != false { fmt.Println("Iteration " + strconv.Itoa(i+1) + " : " + strMessages) } } } if strMode == "parallel" { var intMax int = intCounter - 1 var intTemp int var wg sync.WaitGroup wg.Add(2) intTemp = intCounter / 2 go HowMuchTimeParallel(&wg, 0, intTemp) go HowMuchTimeParallel(&wg, intTemp+1, intMax) wg.Wait() } } func HowMuchTime(i int) { var intCenturies int var intDecades int var intYears int var intMonths int var intWeeks int var intDays int var intHours int var intMinutes int var strMessages string // Set the integers intCenturies = 0 intDecades = 0 intYears = 0 intMonths = 0 intWeeks = 0 intDays = 0 intHours = 0 intMinutes = 0 // Let's get the time to deletion for each entry int64TimeInSeconds := slcTimes[i] // How many centuries? for int64TimeInSeconds >= 3155692600 { intCenturies++ int64TimeInSeconds = int64TimeInSeconds - 3155692600 } // How many decades? for int64TimeInSeconds >= 315569260 { intDecades++ int64TimeInSeconds = int64TimeInSeconds - 315569260 } // How many years? for int64TimeInSeconds >= 31556926 { intYears++ int64TimeInSeconds = int64TimeInSeconds - 31556926 } // How many months? for int64TimeInSeconds >= 2629743 { intMonths++ int64TimeInSeconds = int64TimeInSeconds - 2629743 } // How many weeks? for int64TimeInSeconds >= 604800 { intWeeks++ int64TimeInSeconds = int64TimeInSeconds - 604800 } // How many days? for int64TimeInSeconds >= 86400 { intDays++ int64TimeInSeconds = int64TimeInSeconds - 86400 } // How many hours? for int64TimeInSeconds >= 3600 { intHours++ int64TimeInSeconds = int64TimeInSeconds - 3600 } // How many minutes? for int64TimeInSeconds >= 60 { intMinutes++ int64TimeInSeconds = int64TimeInSeconds - 60 } // Convert to strings strCenturies := strconv.Itoa(intCenturies) strDecades := strconv.Itoa(intDecades) strYears := strconv.Itoa(intYears) strMonths := strconv.Itoa(intMonths) strWeeks := strconv.Itoa(intWeeks) strDays := strconv.Itoa(intDays) strHours := strconv.Itoa(intHours) strMinutes := strconv.Itoa(intMinutes) // Formatting strCenturies = strCenturies + " Centuries " strDecades = strDecades + " Decades " strYears = strYears + " Years " strMonths = strMonths + " Months " strWeeks = strWeeks + " Weeks " strDays = strDays + " Days " strHours = strHours + " Hours " strMinutes = strMinutes + " Minutes " strMessages = "From " + strconv.FormatInt(slcTimes[i], 10) + " : " + strCenturies + strDecades + strYears + strMonths + strWeeks + strDays + strHours + strMinutes if boolSilent != false { fmt.Println("Iteration " + strconv.Itoa(i+1) + " : " + strMessages) } } func HowMuchTimeMassive(wg *sync.WaitGroup, i int) { var intCenturies int var intDecades int var intYears int var intMonths int var intWeeks int var intDays int var intHours int var intMinutes int var strMessages string // Set the integers intCenturies = 0 intDecades = 0 intYears = 0 intMonths = 0 intWeeks = 0 intDays = 0 intHours = 0 intMinutes = 0 // Let's get the time to deletion for each entry int64TimeInSeconds := slcTimes[i] // How many centuries? for int64TimeInSeconds >= 3155692600 { intCenturies++ int64TimeInSeconds = int64TimeInSeconds - 3155692600 } // How many decades? for int64TimeInSeconds >= 315569260 { intDecades++ int64TimeInSeconds = int64TimeInSeconds - 315569260 } // How many years? for int64TimeInSeconds >= 31556926 { intYears++ int64TimeInSeconds = int64TimeInSeconds - 31556926 } // How many months? for int64TimeInSeconds >= 2629743 { intMonths++ int64TimeInSeconds = int64TimeInSeconds - 2629743 } // How many weeks? for int64TimeInSeconds >= 604800 { intWeeks++ int64TimeInSeconds = int64TimeInSeconds - 604800 } // How many days? for int64TimeInSeconds >= 86400 { intDays++ int64TimeInSeconds = int64TimeInSeconds - 86400 } // How many hours? for int64TimeInSeconds >= 3600 { intHours++ int64TimeInSeconds = int64TimeInSeconds - 3600 } // How many minutes? for int64TimeInSeconds >= 60 { intMinutes++ int64TimeInSeconds = int64TimeInSeconds - 60 } // Convert to strings strCenturies := strconv.Itoa(intCenturies) strDecades := strconv.Itoa(intDecades) strYears := strconv.Itoa(intYears) strMonths := strconv.Itoa(intMonths) strWeeks := strconv.Itoa(intWeeks) strDays := strconv.Itoa(intDays) strHours := strconv.Itoa(intHours) strMinutes := strconv.Itoa(intMinutes) // Formatting strCenturies = strCenturies + " Centuries " strDecades = strDecades + " Decades " strYears = strYears + " Years " strMonths = strMonths + " Months " strWeeks = strWeeks + " Weeks " strDays = strDays + " Days " strHours = strHours + " Hours " strMinutes = strMinutes + " Minutes " strMessages = "From " + strconv.FormatInt(slcTimes[i], 10) + " : " + strCenturies + strDecades + strYears + strMonths + strWeeks + strDays + strHours + strMinutes if boolSilent != false { fmt.Println("Iteration " + strconv.Itoa(i+1) + " : " + strMessages) } wg.Done() } func HowMuchTimeParallel(wg *sync.WaitGroup, min int, max int) { var intCenturies int var intDecades int var intYears int var intMonths int var intWeeks int var intDays int var intHours int var intMinutes int var strMessages string // Set the integers intCenturies = 0 intDecades = 0 intYears = 0 intMonths = 0 intWeeks = 0 intDays = 0 intHours = 0 intMinutes = 0 for i := min; i <= max; i++ { // Let's get the time to deletion for each entry int64TimeInSeconds := slcTimes[i] // How many centuries? for int64TimeInSeconds >= 3155692600 { intCenturies++ int64TimeInSeconds = int64TimeInSeconds - 3155692600 } // How many decades? for int64TimeInSeconds >= 315569260 { intDecades++ int64TimeInSeconds = int64TimeInSeconds - 315569260 } // How many years? for int64TimeInSeconds >= 31556926 { intYears++ int64TimeInSeconds = int64TimeInSeconds - 31556926 } // How many months? for int64TimeInSeconds >= 2629743 { intMonths++ int64TimeInSeconds = int64TimeInSeconds - 2629743 } // How many weeks? for int64TimeInSeconds >= 604800 { intWeeks++ int64TimeInSeconds = int64TimeInSeconds - 604800 } // How many days? for int64TimeInSeconds >= 86400 { intDays++ int64TimeInSeconds = int64TimeInSeconds - 86400 } // How many hours? for int64TimeInSeconds >= 3600 { intHours++ int64TimeInSeconds = int64TimeInSeconds - 3600 } // How many minutes? for int64TimeInSeconds >= 60 { intMinutes++ int64TimeInSeconds = int64TimeInSeconds - 60 } // Convert to strings strCenturies := strconv.Itoa(intCenturies) strDecades := strconv.Itoa(intDecades) strYears := strconv.Itoa(intYears) strMonths := strconv.Itoa(intMonths) strWeeks := strconv.Itoa(intWeeks) strDays := strconv.Itoa(intDays) strHours := strconv.Itoa(intHours) strMinutes := strconv.Itoa(intMinutes) // Formatting strCenturies = strCenturies + " Centuries " strDecades = strDecades + " Decades " strYears = strYears + " Years " strMonths = strMonths + " Months " strWeeks = strWeeks + " Weeks " strDays = strDays + " Days " strHours = strHours + " Hours " strMinutes = strMinutes + " Minutes " strMessages = " From " + strconv.FormatInt(slcTimes[i], 10) + " : " + strCenturies + strDecades + strYears + strMonths + strWeeks + strDays + strHours + strMinut es if boolSilent != false { fmt.Println("Iteration " + strconv.Itoa(i+1) + " : " + strMessages) } } wg.Done() }