The file created by tempnam() will have file permissions that reflect the current umask applied to the default (e.g., 0600 or -rw-------). This is the case whether the umask is set before starting the web server process, or set by an earlier call to PHP's umask() function.
For example, if the current umask is 0022, the temporary file is created with permissions 0600 (read/write by owner).
Also, if the current umask is 0222, the temporary file is created with permissions 0400 (read-only by owner). (This is problematic if your code then tries to open the temporary file for writing.)
It's important to remember that the umask revokes permissions. In neither of the above examples are the group, other, or execute permissions set.
See: umask(), chmod().
