How do I programmatically change file permissions?

Question

In Java, I'm dynamically creating a set of files and I'd like to change the file permissions on these files on a linux/unix file system. I'd like to be able to execute the Java equivalent of chmod. Is that possible Java 5? If so, how?

I know in Java 6 the File object has setReadable()/setWritable() methods. I also know I could make a system call to do this, but I'd like to avoid that if possible.

Note for others: For existing files, since Java 7, you can use this one-liner: `Files.setPosixFilePermissions(path, PosixFilePermissions.fromString("rwxr-x---"))` — tom, May 15 '19 at 08:09

erickson · Accepted Answer · 2019-01-04T17:17:08.877

131

Full control over file attributes is available in Java 7, as part of the "new" New IO facility (NIO.2). For example, POSIX permissions can be set on an existing file with setPosixFilePermissions(), or atomically at file creation with methods like createFile() or newByteChannel().

You can create a set of permissions using EnumSet.of(), but the helper method PosixFilePermissions.fromString() will uses a conventional format that will be more readable to many developers. For APIs that accept a FileAttribute, you can wrap the set of permissions with with PosixFilePermissions.asFileAttribute().

Set<PosixFilePermission> ownerWritable = PosixFilePermissions.fromString("rw-r--r--");
FileAttribute<?> permissions = PosixFilePermissions.asFileAttribute(ownerWritable);
Files.createFile(path, permissions);

In earlier versions of Java, using native code of your own, or exec-ing command-line utilities are common approaches.

edited Jan 04 '19 at 17:17

answered Mar 19 '09 at 23:24

erickson

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selecting this one as I don't have the ability to use Marty Lamb's answer. – Roy Rico Mar 20 '09 at 00:44
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I seriously cannot believe that it's been over six years since they started working on NIO.2 and it's still not in a shipping JRE. – clee Feb 03 '10 at 07:49
Yes, it's been a long time in coming. – erickson Feb 03 '10 at 16:13
11

Code example might be useful in your answer. – Ricardo Gladwell Sep 16 '13 at 16:00
Possible disadvantages of setPosixFilePermissions(): It cannot be used to set the setuid, setgid or sticky bits. It does not support numeric file modes, only String ones, although one could always write one's own conversion code. The JNA-based solution given by Marty Lamb below has neither of these disadvantages. – Simon Kissane Oct 14 '13 at 03:28
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This answer http://stackoverflow.com/a/32331442/290182 by @PixelsTech is superior since it provides example code – beldaz May 30 '16 at 23:42
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@SteveB All set. – erickson Jul 23 '18 at 16:37

score 50 · Answer 2 · edited Oct 29 '16 at 11:45

Prior to Java 6, there is no support of file permission update at Java level. You have to implement your own native method or call Runtime.exec() to execute OS level command such as chmod.

Starting from Java 6, you can useFile.setReadable()/File.setWritable()/File.setExecutable() to set file permissions. But it doesn't simulate the POSIX file system which allows to set permission for different users. File.setXXX() only allows to set permission for owner and everyone else.

Starting from Java 7, POSIX file permission is introduced. You can set file permissions like what you have done on *nix systems. The syntax is :

File file = new File("file4.txt");
file.createNewFile();

Set<PosixFilePermission> perms = new HashSet<>();
perms.add(PosixFilePermission.OWNER_READ);
perms.add(PosixFilePermission.OWNER_WRITE);

Files.setPosixFilePermissions(file.toPath(), perms);

This method can only be used on POSIX file system, this means you cannot call it on Windows system.

For details on file permission management, recommend you to read this post.

Marty Lamb · Answer 3 · 2009-03-20T00:08:34.030

45

In addition to erickson's suggestions, there's also jna, which allows you to call native libraries without using jni. It's shockingly easy to use, and I've used it on a couple of projects with great success.

The only caveat is that it's slower than jni, so if you're doing this to a very large number of files that might be an issue for you.

(Editing to add example)

Here's a complete jna chmod example:

import com.sun.jna.Library;
import com.sun.jna.Native;

public class Main {
    private static CLibrary libc = (CLibrary) Native.loadLibrary("c", CLibrary.class);

    public static void main(String[] args) {
        libc.chmod("/path/to/file", 0755);
    }
}

interface CLibrary extends Library {
    public int chmod(String path, int mode);
}

edited Mar 20 '09 at 00:08

answered Mar 19 '09 at 23:30

Marty Lamb

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JNA is such a nice tool for native calls! – erickson Mar 20 '09 at 04:32
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For correct error handling, CLibrary.chmod() must be declared to throw com.sun.jna.LastErrorException. That is the only thread-safe way of getting the errno value set by the chmod() call. Otherwise, you can get the success/fail status from the return value, but not the actual error code. – Simon Kissane Oct 14 '13 at 03:23

score 22 · Answer 4 · edited Feb 03 '21 at 14:55

22

For Windows 7 with NIO 2:

public static void main(String[] args) throws IOException {
    Path file = Paths.get("c:/touch.txt");
    AclFileAttributeView aclAttr = Files.getFileAttributeView(file, AclFileAttributeView.class);
    System.out.println(aclAttr.getOwner());
    for (AclEntry aclEntry : aclAttr.getAcl()) {
        System.out.println(aclEntry);
    }
    System.out.println();
    
    UserPrincipalLookupService upls = file.getFileSystem().getUserPrincipalLookupService();
    UserPrincipal user = upls.lookupPrincipalByName(System.getProperty("user.name"));
    AclEntry.Builder builder = AclEntry.newBuilder();       
    builder.setPermissions( EnumSet.of(AclEntryPermission.READ_DATA, AclEntryPermission.EXECUTE, 
            AclEntryPermission.READ_ACL, AclEntryPermission.READ_ATTRIBUTES, AclEntryPermission.READ_NAMED_ATTRS,
            AclEntryPermission.WRITE_ACL, AclEntryPermission.DELETE
    ));
    builder.setPrincipal(user);
    builder.setType(AclEntryType.ALLOW);
    aclAttr.setAcl(Collections.singletonList(builder.build()));
}

edited Feb 03 '21 at 14:55

Lii

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answered Dec 15 '12 at 14:10

bob

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this works great. The only modification done was for the lookupPrincipalByName() method, I sent System.getProperty("user.name") instead of "user". Finally it looked like upls.lookupPrincipalByName(System.getProperty("user.name")); Thanks for the code! – isuru chathuranga Aug 06 '13 at 10:44
@bob.. can you give me AclFileAttributeView and UserPrincipalLookupService class.. bcz it cant resolve.. you answer seems to be working.. and i want to implement – Sagar Chavada Jul 08 '16 at 07:33
java.nio.file.attribute.AclFileAttributeView and java.nio.file.attribute.UserPrincipalLookupService, it require jdk 1.7+ to compile and run. – bob Jul 09 '16 at 16:50
I'm having the strangest result with this approach. I printed out the user, and it is my current active user. Yet I get access denied both in java, but also in windows when going to that file. I can't currently explain what is happening. – Kalec Aug 31 '21 at 14:27

score 13 · Answer 5 · answered Apr 11 '19 at 03:22

13

Just to update this answer unless anyone comes across this later, since JDK 6 you can use

File file = new File('/directory/to/file');
file.setWritable(boolean);
file.setReadable(boolean);
file.setExecutable(boolean);

you can find the documentation on Oracle File(Java Platform SE 7). Bear in mind that these commands only work if the current working user has ownership or write access to that file. I am aware that OP wanted chmod type access for more intricate user configuration. these will set the option across the board for all users.

answered Apr 11 '19 at 03:22

TravisF

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Cool, le sauveur! – khawarizmi Apr 18 '19 at 10:34
I have tested it yet with Openjdk 11.0.6 under Debian, it works! – Hartmut Schorrig Mar 10 '20 at 13:10

score 12 · Answer 6 · edited May 07 '18 at 13:37

If you want to set 777 permission to your created file than you can use the following method:

public void setPermission(File file) throws IOException{
    Set<PosixFilePermission> perms = new HashSet<>();
    perms.add(PosixFilePermission.OWNER_READ);
    perms.add(PosixFilePermission.OWNER_WRITE);
    perms.add(PosixFilePermission.OWNER_EXECUTE);

    perms.add(PosixFilePermission.OTHERS_READ);
    perms.add(PosixFilePermission.OTHERS_WRITE);
    perms.add(PosixFilePermission.OTHERS_EXECUTE);

    perms.add(PosixFilePermission.GROUP_READ);
    perms.add(PosixFilePermission.GROUP_WRITE);
    perms.add(PosixFilePermission.GROUP_EXECUTE);

    Files.setPosixFilePermissions(file.toPath(), perms);
}

score 2 · Answer 7 · answered Dec 15 '13 at 08:18

Apache ant chmod (not very elegant, adding it for completeness) credit shared with @msorsky

    Chmod chmod = new Chmod();
    chmod.setProject(new Project());
    FileSet mySet = new FileSet();
    mySet.setDir(new File("/my/path"));
    mySet.setIncludes("**");
    chmod.addFileset(mySet);
    chmod.setPerm("+w");
    chmod.setType(new FileDirBoth());
    chmod.execute();

Uddhav P. Gautam · Answer 8 · 2020-08-03T20:35:14.627

import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.attribute.FileAttribute;
import java.nio.file.attribute.PosixFileAttributes;
import java.nio.file.attribute.PosixFilePermission;
import java.nio.file.attribute.PosixFilePermissions;
import java.util.Set;

public class FileAndDirectory1 {
    public static void main(String[] args) {
        
        File file = new File("fileTest1.txt");
        System.out.println(file.getAbsoluteFile());
        try {
            //file.createNewFile();
            if(!file.exists())
            {
                //PosixFilePermission is an enum class, PosixFilePermissions is a final class
                
                //create file permissions from string
                Set<PosixFilePermission> filePermissions = PosixFilePermissions.fromString("---------"/* "rwxrwxrwx" */);
                FileAttribute<?> permissions = PosixFilePermissions.asFileAttribute(filePermissions);
                Files.createFile(file.toPath(), permissions);
                // printing the permissions associated with the file
                System.out.println("Executable: " + file.canExecute());
                System.out.println("Readable: " + file.canRead());
                System.out.println("Writable: "+ file.canWrite());

                file.setExecutable(true);
                file.setReadable(true);
                file.setWritable(true);
            }
            else
            {
                //modify permissions
                
                //get the permission using file attributes
                Set<PosixFilePermission> perms = Files.readAttributes(file.toPath(), PosixFileAttributes.class).permissions();
                perms.remove(PosixFilePermission.OWNER_WRITE);

                perms.add(PosixFilePermission.OWNER_READ);
                perms.add(PosixFilePermission.OWNER_EXECUTE);
                perms.add(PosixFilePermission.GROUP_WRITE);
                perms.add(PosixFilePermission.GROUP_READ);
                perms.add(PosixFilePermission.GROUP_EXECUTE);
                perms.add(PosixFilePermission.OTHERS_WRITE);
                perms.add(PosixFilePermission.OTHERS_READ);
                perms.add(PosixFilePermission.OTHERS_EXECUTE);
                Files.setPosixFilePermissions(file.toPath(), perms);

                System.out.println("Executable: " + file.canExecute());
                System.out.println("Readable: " + file.canRead());
                System.out.println("Writable: "+ file.canWrite());

                file.delete();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        Path path = Paths.get(String.valueOf(file));
        System.out.println(path);
    }
}

score 2 · Answer 9 · edited Aug 24 '13 at 22:42

2

You can use the methods of the File class: http://docs.oracle.com/javase/7/docs/api/java/io/File.html

edited Aug 24 '13 at 22:42

davelupt

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answered Sep 26 '11 at 06:23

Erel Segal-Halevi

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Please have a second look at the question. Roy Rico knows about setReadable() and setWritable(), but they only let you change owner permissions, not group or everyone permissions, or any of the other flags. – Chrissi Jan 05 '15 at 20:40

score 1 · Answer 10 · answered Mar 31 '13 at 18:00

1

for Oralce Java 6:

private static int chmod(String filename, int mode) {
    try {
        Class<?> fspClass = Class.forName("java.util.prefs.FileSystemPreferences");
        Method chmodMethod = fspClass.getDeclaredMethod("chmod", String.class, Integer.TYPE);
        chmodMethod.setAccessible(true);
        return (Integer)chmodMethod.invoke(null, filename, mode);
    } catch (Throwable ex) {
        return -1;
    }
}

works under solaris/linux.

answered Mar 31 '13 at 18:00

Vlad

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one should be aware that `FileSystemPreferences` spwans a `Timer` daemon thread once it's loaded. it also adds a shutdown hook, but for some applications this may still be problematic. – thrau Oct 16 '16 at 12:08
It's almost always a bad idea to call internal methods like this. – A248 May 29 '21 at 17:11

score 1 · Answer 11 · answered Sep 16 '15 at 08:51

1

There is an example class on Oracle Docs which works very much similar to the UNIX chmod. It works with java se 7+ though.

answered Sep 16 '15 at 08:51

jan.supol

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score 1 · Answer 12 · answered Dec 30 '22 at 10:51

1

Permission 777 is the same as rwxrwxrwx which you can set as follows:

Files.setPosixFilePermissions(path, PosixFilePermissions.fromString("rwxrwxrwx"))

answered Dec 30 '22 at 10:51

Arvind Kumar Avinash

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How do I programmatically change file permissions?

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