How to set group id on execution bit (s) permission using java

Question

I'm trying to set the next set of posix permissions rwxrwsr-x to a folder that I'm creating in java, but haven't had success on this. I tried the next code:

Set<PosixFilePermission> posixPermissions = PosixFilePermissions.fromString("rwxrwsr-x");
Files.setPosixFilePermissions(someDir, posixPermissions);

but I'm getting the next Exception:

java.lang.IllegalArgumentException: Invalid mode

I spent some time looking for a way to do this, but I couldn't find anything. I know I can use ProcessBuilder class to run a command in the OS to set those permissions, but I wanted to do this purely in Java. I need to set those permissions so any file created inside that directory "inherits" the group of the directory.

Answer 1

According to the documentation you are only allowed to use the characters 'r','w','x' and '-'. But in your code snippet you are using 's', which is illegal of course. It should be like this to work:

Set<PosixFilePermission> posixPermissions = PosixFilePermissions.fromString("rwxrwxr-x");
Files.setPosixFilePermissions(someDir, posixPermissions);

Setuid (+s) ist not possible in pure Java, because it's a OS-specific feature.