File Status Flags - The GNU C Library

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### 13.14 File Status Flags

File status flags are used to specify attributes of the opening of a file. Unlike the file descriptor flags discussed in Descriptor Flags, the file status flags are shared by duplicated file descriptors resulting from a single opening of the file. The file status flags are specified with the flags argument to `open`; see Opening and Closing Files.

File status flags fall into three categories, which are described in the following sections.

- Access Modes, specify what type of access is allowed to the file: reading, writing, or both. They are set by `open` and are returned by `fcntl`, but cannot be changed.
- Open-time Flags, control details of what `open` will do. These flags are not preserved after the `open` call.
- Operating Modes, affect how operations such as `read` and `write` are done. They are set by `open`, and can be fetched or changed with `fcntl`.

The symbols in this section are defined in the header file `fcntl.h`.