UNIX for Dummies Questions & Answers

What access modes (permissions) are given to new files you create?

That's configurable. You set it with your umask. And what permissions you get depends on what permissions you ask for, too.
open("filename", O_RDWR|O_CREAT, 0000); will only create a file with 0000 permissions no matter what your umask is.

A file created with a umask of 000 can have up to 777 permissions, that is, rwxrwxrwx.

A file created with a umask of 022 can have up to 755 permissons, that is, rwxr-xr-x.

If you're creating these files with the shell, it will always strip the executable bits off. So even a umask of 000 would only create rw-rw-rw files.

You can set your umask in the shell like umask 0777 or in C like umask(0777)

When I login to my system I end up with a 022 umask by default.

I applaud Corona688 for his/her knowledge and experience, but I don't think they explained it in layman's terms well enough. @ Corona688 - Kudos.

You might set your 'umask' in ~/.profile or maybe your shell specific version, for me it is ~/.bash_profile.

The umask setting is a subtractive octal value from 777 for dirs, and from 666 for files. For example, if your umask is set to 022, when you `mkdir mynewdir`, the directory has octal permissions of 755. And when you create a new file, the file has octal permissions of 644.

Hope that helped!