`strace -f` to trace child process that&#39;s `fork()`ed.

I can&#39;t see an easy way:

You could use the `-ff` option with `-o filename` to produce multiple files (one per pid). 

eg:

    strace -o process_dump -ff ./executable
    grep clone process_dump*


that would help you see which parent created what. Maybe that would help you - at least then you could search backwards.

There is a perl script called `strace-graph`.  Here is a [version from github][1].  It is packaged with **crosstool-ng** versions of compilers.  It works for me even used cross platform.

# ARM Linux box.

    $ ./strace -f -q -s 100 -o app.trc -p 449
    $ tftp -pr app.trc 172.0.0.133

# X86_64 Linux box.

    $ ./strace-graph /srv/tftp/app.trc 
     (anon)
      +-- touch /tmp/ppp.sleep
      +-- killall -HUP pppd
      +-- amixer set Speaker 70%
      +-- amixer set Speaker 70%
      +-- amixer set Speaker 70%
      +-- amixer set Speaker 70%
      +-- amixer set Speaker 50%
      +-- amixer set Speaker 70%
      `-- amixer set Speaker 50%

The output can be used to help navigate the main trace log.

  [1]: https://github.com/strace/strace/blob/master/src/strace-graph

To capture traffic for a single process you can use `strace`, as @stackmate suggested.

    strace -f -e trace=network -s 10000 -p &lt;PID&gt;;

or output it to a file.

    strace -f -e trace=network -s 10000 -o dumpfile -p &lt;PID&gt;

`-f` for all forked process, `-s` for string size to print, and `-o` to dump the output to a file.

I have a map which shows correctly, the only thing I want to do now is set the zoom level when it loads. Is there a way to do this?

Thanks

Setting the zoom level for a MKMapView

OK, I&#39;m losing it. PowerShell is annoying me. I&#39;d like a pause dialog to appear, and it won&#39;t.

    PS W:\&gt;&gt;&gt; $host.UI.RawUI.ReadKey(&quot;NoEcho,IncludeKeyDown&quot;)
    Exception calling &quot;ReadKey&quot; with &quot;1&quot; argument(s): &quot;The method or operation is not implemented.&quot;
    At line:1 char:23
    + $host.UI.RawUI.ReadKey &lt;&lt;&lt;&lt; (&quot;NoEcho&quot;)
        + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
        + FullyQualifiedErrorId : DotNetMethodException


How do you do a ‘Pause’ with PowerShell 2.0?

I used `strace` to attach to a process briefly. The process created 90 threads. When I found the offending thread, I had to tediously search for the parent thread, then the grandparent thread, and so on all the way to the root process.

Is there a trick or tool to quickly figure out which thread created another? Or better yet, print the tree of thread creations like `pstree`? 


How to track child process using strace?

<p>I used <code>strace</code> to attach to a process briefly. The process created 90 threads. When I found the offending thread, I had to tediously search for the parent thread, then the grandparent thread, and so on all the way to the root process.</p>
<p>Is there a trick or tool to quickly figure out which thread created another? Or better yet, print the tree of thread creations like <code>pstree</code>?</p>


I want to run a shell script when a specific file or directory changes.

How can I easily do that?

How to run a shell script when a file or directory changes?

I want to create a clone of the structure of our multi-terabyte file server.  I know that cp --parents can move a file and it&#39;s parent structure, but is there any way to copy the directory structure intact? 

I want to copy to a linux system and our file server is CIFS mounted there.

Copy folder structure (without files) from one location to another

Can someone post a simple example of using named pipes in Bash on Linux?

Example of using named pipes in Linux shell (Bash)

Can someone please explain the difference between preemptive Threading model and Non Preemptive threading model?  
 
As per my understanding:  

* ***Non Preemptive threading model:***  Once a thread is started it cannot be stopped or the control cannot be transferred to other threads until the thread has completed its task.  
* ***Preemptive Threading Model:*** The runtime is allowed to step in and hand control from one thread to another at any time. Higher priority threads are given precedence over Lower priority threads.   

Can someone please:

 1. Explain if the understanding is correct.
 2. Explain the advantages and disadvantages of both models.
 3. An example of when to use what will be really helpful.
 4. If i create a thread in Linux (system v or Pthread) without mentioning any options(are there any??) by default the threading model used is preemptive threading model?



Preemptive threads Vs Non Preemptive threads

Can someone provide the steps needed to install python version 2.7 on SUSE and RedHat?  It version that is on there is like 2.4 and I need to have it at at least 2.6 to make my script work.
So after the install, I can type Python in a xTerm and get the Python 2.7 command line interface.

On linux SUSE or RedHat, how do I load Python 2.7

I&#39;m trying to run two AsyncTasks at the same time. (Platform is Android 1.5, HTC Hero.)
However, only the first gets executed. Here&#39;s a simple snippet to describe my problem:

    public class AndroidJunk extends Activity {
     class PrinterTask extends AsyncTask&lt;String, Void, Void&gt; {
         protected Void doInBackground(String ... x) {
          while (true) {
           System.out.println(x[0]);
           try {
            Thread.sleep(1000);
           } catch (InterruptedException ie) {
            ie.printStackTrace();
           }
          }
            }
        };
 
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.main);
        
            new PrinterTask().execute(&quot;bar bar bar&quot;);
            new PrinterTask().execute(&quot;foo foo foo&quot;);

            System.out.println(&quot;onCreate() is done.&quot;);
        }
    }

The output I expect is:

    onCreate() is done.
    bar bar bar
    foo foo foo
    bar bar bar
    foo foo foo

And so on. However, what I get is:

    onCreate() is done.
    bar bar bar
    bar bar bar
    bar bar bar

The second AsyncTask never gets executed. If I change the order of the execute() statements, only the foo task will produce output.

Am I missing something obvious here and/or doing something stupid? Is it not possible to run two AsyncTasks at the same time?


Edit: I realized the phone in question runs Android 1.5, I updated the problem descr. accordingly. I don&#39;t have this problem with an HTC Hero running Android 2.1. Hmmm ...

Running multiple AsyncTasks at the same time -- not possible?

I&#39;m hoping someone can enlighten me as to what could possibly be causing this error:

&gt;Attempted to read or write protected memory. This is often an indication that other memory is corrupt.

I cannot really post code because this error seems to get thrown in any random area of the application. The application will run anywhere from 12-48 hours before throwing the error. Sometimes it will stop in a seemingly random spot and throw the above error, other times the entire application stops and I get a screen with an error that says something along the lines of &quot;There was a fatal error in... This may be a bug in the CLR or...&quot; something about PInvoke or other non relevant info. When this happens all threads show terminated and there is no debugging information available. 

In a nutshell this is what the application does:

Its a multi-threaded server application written in entirely in C#. Clients connect to the server via socket. The server runs a virtual &quot;environment&quot; for the clients where they can interact with each other and the environment. It consumes quite a bit of memory but I do not see it leaking. It typically consumes about 1.5GB.  I dont think its leaking because the memory usage stays relatively constant the entire time the application is running. Its constantly running code to maintain the environment even if the clients are not doing anything. It uses no 3rd party software or other APIs. The only outside resources this application uses is socket connections and SQL database connections. Its running on a 64bit server. I have tried debugging this in VS2008 &amp; VS2010 using .net 2.0, 3.5, and 4.0 and on multiple servers and the problem still eventually occurs. 

I&#39;ve tried turning off compiler optimizations and several microsoft hot-fixes. Nothing seems to make this issue go away. It would be appreciated if anyone knows any possible causes, or some kind of way to identify whats causing the problem.

 

Attempted to read or write protected memory. This is often an indication that other memory is corrupt

The Qt documentation for QThread says to create a class from QThread, and to implement the run method. 

Below is taken from the 4.7 Qthread documentation...

&gt; To create your own threads, subclass QThread and reimplement run(). For example: 
    
     class MyThread : public QThread
     {
     public:
         void run();
     };
    
     void MyThread::run()
     {
         QTcpSocket socket;
         // connect QTcpSocket&#39;s signals somewhere meaningful
         ...
         socket.connectToHost(hostName, portNumber);
         exec();
     }

So in every single thread I&#39;ve created, I&#39;ve done just that and for most things it works just fine (I do not implement moveToThread(this) in any of my objects and it works great).

I hit a snag last week (managed to get through it by working around where I created my objects) and found the [following blog post][1]. Here is basically says that subclassing QThread really isn&#39;t the correct way to do it (and that the documentation is incorrect).

This is coming from a Qt developer so at first glance I was interested and upon further reflection, agree with him. Following OO principles, you really only want to subclass a class to further enhance that class... not to just use the classes methods directly... thats why you instantiate... 

Lets say I wanted to move a custom QObject class to a thread... what would be the &#39;correct&#39; way of doing it? In that blog post, he &#39;says&#39; he has an example somewhere... but if someone could further explain it to me it&#39;d be greatly appreciated!

**Update:**

Since this question gets so much attention, here is a copy and paste of the 4.8 documentation with the &#39;proper&#39; way to implement a QThread.

 

    class Worker : public QObject
     {
         Q_OBJECT
         QThread workerThread;
    
     public slots:
         void doWork(const QString &amp;parameter) {
             // ...
             emit resultReady(result);
         }
    
     signals:
         void resultReady(const QString &amp;result);
     };
    
     class Controller : public QObject
     {
         Q_OBJECT
         QThread workerThread;
     public:
         Controller() {
             Worker *worker = new Worker;
             worker-&gt;moveToThread(&amp;workerThread);
             connect(workerThread, SIGNAL(finished()), worker, SLOT(deleteLater()));
             connect(this, SIGNAL(operate(QString)), worker, SLOT(doWork(QString)));
             connect(worker, SIGNAL(resultReady(QString)), this, SLOT(handleResults(QString)));
             workerThread.start();
         }
         ~Controller() {
             workerThread.quit();
             workerThread.wait();
         }
     public slots:
         void handleResults(const QString &amp;);
     signals:
         void operate(const QString &amp;);
     };

I still believe that it is worthwhile to point out that they include an extra `Worker::workerThread` member that is unnecessary and is never used in their example. Remove that piece and it is a proper example of how to do threading in Qt.

  [1]: http://blog.qt.io/blog/2010/06/17/youre-doing-it-wrong/

what is the correct way to implement a QThread... (example please...)

The javadoc for SimpleDateFormat states that SimpleDateFormat is not synchronized.

&gt; &quot;Date formats are not synchronized. It
&gt; is recommended to create separate
&gt; format instances for each thread. If
&gt; multiple threads access a format
&gt; concurrently, it must be synchronized
&gt; externally.&quot;

But what is the best approach to using an instance of SimpleDateFormat in a multi threaded environment. Here are a few options I have thought of, I have used options 1 and 2 in the past but I am curious to know if there are any better alternatives or which of these options would offer the best performance and concurrency.

Option 1: Create local instances when required

    public String formatDate(Date d) {
        SimpleDateFormat sdf = new SimpleDateFormat(&quot;yyyy-MM-dd&quot;);
        return sdf.format(d);
    }

Option 2: Create an instance of SimpleDateFormat as a class variable but synchronize access to it.

    private SimpleDateFormat sdf = new SimpleDateFormat(&quot;yyyy-MM-dd&quot;);
    public String formatDate(Date d) {
        synchronized(sdf) {
            return sdf.format(d);
        }
    }

Option 3: Create a ThreadLocal to store a different instance of SimpleDateFormat for each thread.

    private ThreadLocal&lt;SimpleDateFormat&gt; tl = new ThreadLocal&lt;SimpleDateFormat&gt;();
    public String formatDate(Date d) {
        SimpleDateFormat sdf = tl.get();
        if(sdf == null) {
            sdf = new SimpleDateFormat(&quot;yyyy-MM-hh&quot;);
            tl.set(sdf);
        }
        return sdf.format(d);
    }


Synchronizing access to SimpleDateFormat

In C# 4.0, we have `Task` in the *System.Threading.Tasks* namespace. What is the true difference between `Thread` and `Task`. I did some sample program(help taken from MSDN)  for my own sake of learning with 

    Parallel.Invoke 
    Parallel.For 
    Parallel.ForEach 

but have many doubts as the idea is not so clear. 

I have initially searched in Stackoverflow for a similar type of question but may be with this question title I was not able to get the same. If anyone knows about the same type of question being posted here earlier, kindly give the reference of the link.

What is the difference between task and thread?

I&#39;m trying to use strace to find out what commands a program executes using `execve`. Some of the arguments in these commands are quite long, and strace is abbreviating the arguments to `execve` (I see &quot;...&quot; after about 30 characters), preventing me from getting any useful information. How can I get the full text of each argument?

I&#39;ve read the [man page][1]. The -v option prints the environment, which is useful, but the arguments are still truncated.

    strace -f -e trace=execve -v -p 1234

I also tried passing verbose=all, but this just gives some extra information about SIGCHLD.

    strace -f -e verbose=all trace=execve -v -p 1234


  [1]: http://linux.die.net/man/1/strace

Prevent strace from abbreviating arguments?

I do know that `strace` uses `ptrace` to do the job,

but it needs to run the target process with `TRACE_ME` on,

which don&#39;t apply for the case of an already running process.

how does it work on an already running process?

How does strace connect to an already running process?

I&#39;m trying to attach a program with gdb but it returns:

&gt; Attaching to process 29139  
&gt;     Could not attach to process.  If your uid matches the uid of the target
&gt;     process, check the setting of /proc/sys/kernel/yama/ptrace_scope, or try
&gt;     again as the root user.  For more details, see /etc/sysctl.d/10-ptrace.conf  
&gt;     ptrace: Operation not permitted.

gdb-debugger returns &quot;Failed to attach to process, please check privileges and try again.&quot;

strace returns &quot;attach: ptrace(PTRACE_ATTACH, ...): Operation not permitted&quot;

I changed &quot;kernel.yama.ptrace_scope&quot; 1 to 0 and `/proc/sys/kernel/yama/ptrace_scope` 1 to 0 and tried `set environment LD_PRELOAD=./ptrace.so` with this:

    #include &lt;stdio.h&gt;
    int ptrace(int i, int j, int k, int l) {
        printf(&quot; ptrace(%i, %i, %i, %i), returning -1\n&quot;, i, j, k, l);
        return 0;
    }

But it still returns the same error. How can I attach it to debuggers?

How to solve &quot;ptrace operation not permitted&quot; when trying to attach GDB to a process?

I wanted to trace the system calls made by the **find** command [to debug some performance issues](https://stackoverflow.com/questions/31045501/how-to-speed-up-find-for-listing-git-repositories) however I could not figure out how to do this on Mac OS X Yosemite.  How can I trace system calls for an arbitrary program similarly to what **strace** does on FreeBSD?  I am especially interested in tracing file-system related calls.

How to trace system calls of a program in Mac OS X?

I have a python GUI application. And now I need to know what all libraries the application links to. So that I can check the license compatibility of all the libraries.

I have tried using strace, but strace seems to report all the packages even if they are not used by the application.

And, I tried python ModuleFinder but it just returns the modules that are inside python2.7 and not system level packages that are linked.

So is there any way I can get all the libraries that are linked from my application?

Content Type	Original Author	Original Content on Stackoverflow
Question	projectshave	View Question on Stackoverflow
Solution 1 - Linux	Je Rog	View Answer on Stackoverflow
Solution 2 - Linux	stackmate	View Answer on Stackoverflow
Solution 3 - Linux	artless noise	View Answer on Stackoverflow
Solution 4 - Linux	alshaboti	View Answer on Stackoverflow

How to track child process using strace?

Linux Problem Overview

Linux Solutions

Solution 1 - Linux

Solution 2 - Linux

Solution 3 - Linux

ARM Linux box.

X86_64 Linux box.

Solution 4 - Linux

How do you do a ‘Pause’ with PowerShell 2.0?

Setting the zoom level for a MKMapView

Attributions