changing file permissions of default mkstemp

Question

I call the following code in C:

 fileCreatefd = mkstemp(fileName);

I see that the file is created with permissions 600 (-rw-------). I want to create this temp file as -rw-rw-rw-

I tried playing around with umask but that only applies a mask over the file permissions -- at least thats my understanding. So how can i create a file with permissions 666?

Thanks

Answer 1

You cannot create it 0666 with mkstemp. You can change the permissions afterwards, if that is sufficient for your application, with fchmod.

fileCreatefd = mkstemp(fileName);
fchmod(fileCreatefd, 0666)

Answer 2

The mkstemp() function generates a unique temporary filename from template, creates and opens the file, and returns an open file descriptor for the file.

The last six characters of template must be "XXXXXX" and these are replaced with a string that makes the filename unique. Since it will be modified, template must not be a string constant, but should be declared as a character array.

The file is created with permissions 0600, that is, read plus write for owner only. (In glibc versions 2.06 and earlier, the file is created with permissions 0666, that is, read and writefor all users.) The returned file descriptor provides both read and write access to the file. The file is opened with the open(2) O_EXCL flag, guaranteeing that the caller is the process that creates the file.

More generally, the POSIX specification of mkstemp() does not say anything about file modes, so the application should make sure its file mode creation mask (umask(2)) is set appropriately before calling mkstemp() (and mkostemp()).

So after creating the File Use fchmod to change the file permission.