How to run Linux program from Java code

Question

I am trying to create a disk space from Java code using qemu-img so I instantiated process and runtime classes. When run the program the command is not executed though I used the same mechanism for similar execution and it work fine. So I am wondering whether I miss something here.

StringBuilder commandBuilder = new StringBuilder("qemu-img create -f "+chosenStorageType+" ~/"+storageName+".img "+storageSize+"M");
System.out.println(commandBuilder);
String command = commandBuilder.toString();
System.out.println("this is the correct one: "+command);

System.out.println("Creating the image...");
Runtime runtime = Runtime.getRuntime();
Process process = null;
try {
    process = runtime.exec(command);
    System.out.println("from process try..catch");
} catch (IOException e1) {
    e1.printStackTrace();
    System.out.println(e1.getMessage());
}finally{
    System.out.println("from finally entry");
    process.destroy();
}

the output is as following:

qemu-img create -f raw ~/testSPACE.img 23.0M

this is the correct one: /qemu-img create -f raw ~/testSPACE.img 23.0M
Creating the image...
from process try..catch
from finally entry

But if I go to the directory the file isn't created.

Just to test it if I copy the output into terminal everything works like a charm.

Can you verify that ~ is being expanded properly? Try putting a full absolute path in there and see if it works. Sometimes that kind of expansion behaviour is provided by the shell and is therefore not going to work for some command-invocation tasks. — Gian
– Gian, Commented Mar 21, 2013 at 10:05
yeah while providing absolute path: StringBuilder commandBuilder = new StringBuilder("qemu-img create -f "+chosenStorageType+" /home/dartron/"+storageName+".img"+storageSize+"M"); it does the same thing just prints out the lines but doesnt execute the command — user2023107
– user2023107, Commented Mar 21, 2013 at 22:21

Community · Accepted Answer · 2017-05-23 11:57:26Z

1

The tilde (~) here

" ~/"+storageName+".img "

is interpreted by the shell as meaning your home directory. I would substitute the real path.

Note also that you need to be consuming the process stdout/err, and collecting the error code of the process (and checking it!) via Process.waitFor()

edited May 23, 2017 at 11:57

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answered Mar 21, 2013 at 10:05

Brian Agnew

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3 Comments

Perception Over a year ago

To emphasize more strongly, the ~ symbol requires a shell to be interpreted, which a Java Process does not have by default. You would have to invoke the shell as one of your commands, ie, for Linux, by making the first command /usr/bin/sh.

user2023107 Over a year ago

even while providing absolute path: StringBuilder commandBuilder = new StringBuilder("qemu-img create -f "+chosenStorageType+" /home/dartron/"+storageName+".img"+storageSize+"M"); it does the same thing just prints out the lines but doesnt execute the command

artless-noise-bye-due2AI Over a year ago

@user2023107 Try the absolute path to qemu-img as well.

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