Permission denied error in Java for chmod command

问题:

I have an executable file (ffmpeg) that I'm trying to run with a Java program on a Mac. I used the Java program to send the command chmod 777 /path/to/ffmpeg, but when I try to run ffmpeg, I get the following error:

java.io.IOException: Cannot run program "/Users/james/WalkTheHall/ffmpeg": error=13, Permission denied

But when I run chmod 777 /path/to/ffmpeg from Terminal on my own before opening the Java application, the command to ffmpeg will run just fine in the Java program.

Is there a difference between calling chmod from within the Java program and calling it on my own? Why will it not work? Thank you!

回答1:

I'd guess that chmod is a shell command, not an executable. Try running chmod through your shell. See more details here: Want to invoke a linux shell command from Java

回答2:

I just had the same problem in my code. i solved this by add waitFor after exec. The "chmod" process is not finished when next command is executed. the code may look like:

p = Runtime.getRuntime.exec("chmod 777 xxx");
p.waitFor();
Runtime.getRuntime.exec("./xxx");

回答3:

Yes, there is a difference. When you run the command from the terminal, it is you who is performing the action, and thus it is performed using your credentials. The Java application is running the command using the Java application's permissions. This is to prevent an application from running and then making dangerous, unwanted changes to the file system. Perhaps someone else can elaborate and give guidance to a workaround for this.

回答4:

I am currently working on a project that also makes use of FFMpeg on OSX. I store FFMpeg in the JAR and extract it and set executable on use as you seem to be doing. This is what I do, and it seems to work.

public static void setExecutable(File file, boolean executable)
{
    Process p = Runtime.getRuntime().exec(new String[] {
        "chmod",
        "u"+(executable?'+':'-')+"x",
        file.getAbsolutePath(),
    });
    // do stuff to make sure p finishes & capture output
}

The code is GPL, so feel free to check it out. Its not the nicest codebase, and even the FFMpeg stuff is perhaps overly complex, but it works.

Source is viewable at http://korsakow.net

These two files in particular might be interesting for you

FFMpegEncoderOSX.java

FileUtil.java

回答5:

Try this:

File commandFile = new File("myFile.txt");
commandFile.setExecutable(true);
Process p = Runtime.getRuntime.exec(commandFile.getAbsoluteFile());