24.14. Filesystem Configuration — RTEMS Classic API Guide 5.4-rc2 (21st August 2026) documentation

# 24.14. Filesystem Configuration

This section describes configuration options related to filesytems. By default, the In-Memory Filesystem (IMFS) is used as the base filesystem (also known as root filesystem). In order to save some memory for your application, you can disable the filesystem support with the CONFIGURE_APPLICATION_DISABLE_FILESYSTEM configuration option. Alternatively, you can strip down the features of the base filesystem with the CONFIGURE_USE_MINIIMFS_AS_BASE_FILESYSTEM and CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM configuration options. These three configuration options are mutually exclusive. They are intended for an advanced application configuration.

Features of the IMFS can be disabled and enabled with the following configuration options:

- CONFIGURE_IMFS_DISABLE_CHMOD

- CONFIGURE_IMFS_DISABLE_CHOWN

- CONFIGURE_IMFS_DISABLE_LINK

- CONFIGURE_IMFS_DISABLE_MKNOD

- CONFIGURE_IMFS_DISABLE_MKNOD_FILE

- CONFIGURE_IMFS_DISABLE_MOUNT

- CONFIGURE_IMFS_DISABLE_READDIR

- CONFIGURE_IMFS_DISABLE_READLINK

- CONFIGURE_IMFS_DISABLE_RENAME

- CONFIGURE_IMFS_DISABLE_RMNOD

- CONFIGURE_IMFS_DISABLE_SYMLINK

- CONFIGURE_IMFS_DISABLE_UNMOUNT

- CONFIGURE_IMFS_DISABLE_UTIME

- CONFIGURE_IMFS_ENABLE_MKFIFO

## 24.14.1. CONFIGURE_APPLICATION_DISABLE_FILESYSTEM

CONSTANT:

  `CONFIGURE_APPLICATION_DISABLE_FILESYSTEM`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then a base filesystem and the configured filesystems are initialized during system initialization.

DESCRIPTION:

  In case this configuration option is defined, then no base filesystem is initialized during system initialization and no filesystems are configured.

NOTES:

  Filesystems shall be initialized to support file descriptor based device drivers and basic input/output functions such as `printf()`. Filesystems can be disabled to reduce the memory footprint of an application.

## 24.14.2. CONFIGURE_FILESYSTEM_ALL

CONSTANT:

  `CONFIGURE_FILESYSTEM_ALL`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the following configuration options will be defined as well

  - CONFIGURE_FILESYSTEM_DOSFS,

  - CONFIGURE_FILESYSTEM_FTPFS,

  - CONFIGURE_FILESYSTEM_IMFS,

  - CONFIGURE_FILESYSTEM_JFFS2,

  - CONFIGURE_FILESYSTEM_NFS,

  - CONFIGURE_FILESYSTEM_RFS, and

  - CONFIGURE_FILESYSTEM_TFTPFS.

NOTES:

  None.

## 24.14.3. CONFIGURE_FILESYSTEM_DOSFS

CONSTANT:

  `CONFIGURE_FILESYSTEM_DOSFS`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the DOS (FAT) filesystem is registered, so that instances of this filesystem can be mounted by the application.

NOTES:

  This filesystem requires a Block Device Cache configuration, see CONFIGURE_APPLICATION_NEEDS_LIBBLOCK.

## 24.14.4. CONFIGURE_FILESYSTEM_FTPFS

CONSTANT:

  `CONFIGURE_FILESYSTEM_FTPFS`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the FTP filesystem (FTP client) is registered, so that instances of this filesystem can be mounted by the application.

NOTES:

  None.

## 24.14.5. CONFIGURE_FILESYSTEM_IMFS

CONSTANT:

  `CONFIGURE_FILESYSTEM_IMFS`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the In-Memory Filesystem (IMFS) is registered, so that instances of this filesystem can be mounted by the application.

NOTES:

  Applications will rarely need this configuration option. This configuration option is intended for test programs. You do not need to define this configuration option for the base filesystem (also known as root filesystem).

## 24.14.6. CONFIGURE_FILESYSTEM_JFFS2

CONSTANT:

  `CONFIGURE_FILESYSTEM_JFFS2`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the JFFS2 filesystem is registered, so that instances of this filesystem can be mounted by the application.

NOTES:

  None.

## 24.14.7. CONFIGURE_FILESYSTEM_NFS

CONSTANT:

  `CONFIGURE_FILESYSTEM_NFS`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the Network Filesystem (NFS) client is registered, so that instances of this filesystem can be mounted by the application.

NOTES:

  None.

## 24.14.8. CONFIGURE_FILESYSTEM_RFS

CONSTANT:

  `CONFIGURE_FILESYSTEM_RFS`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the RTEMS Filesystem (RFS) is registered, so that instances of this filesystem can be mounted by the application.

NOTES:

  This filesystem requires a Block Device Cache configuration, see CONFIGURE_APPLICATION_NEEDS_LIBBLOCK.

## 24.14.9. CONFIGURE_FILESYSTEM_TFTPFS

CONSTANT:

  `CONFIGURE_FILESYSTEM_TFTPFS`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then the TFTP filesystem (TFTP client) is registered, so that instances of this filesystem can be mounted by the application.

NOTES:

  None.

## 24.14.10. CONFIGURE_IMFS_DISABLE_CHMOD

CONSTANT:

  `CONFIGURE_IMFS_DISABLE_CHMOD`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the root IMFS supports changing the mode of files.

DESCRIPTION:

  In case this configuration option is defined, then the root IMFS does not support changing the mode of files (no support for `chmod()`).

NOTES:

  None.

## 24.14.11. CONFIGURE_IMFS_DISABLE_CHOWN

CONSTANT:

  `CONFIGURE_IMFS_DISABLE_CHOWN`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the root IMFS supports changing the ownership of files.

DESCRIPTION:

  In case this configuration option is defined, then the root IMFS does not support changing the ownership of files (no support for `chown()`).

NOTES:

  None.

## 24.14.12. CONFIGURE_IMFS_DISABLE_LINK

CONSTANT:

  `CONFIGURE_IMFS_DISABLE_LINK`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the root IMFS supports hard links.

DESCRIPTION:

  In case this configuration option is defined, then the root IMFS does not support hard links (no support for `link()`).

NOTES:

  None.

## 24.14.13. CONFIGURE_IMFS_DISABLE_MKNOD

CONSTANT:

  `CONFIGURE_IMFS_DISABLE_MKNOD`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the root IMFS supports making files.

DESCRIPTION:

  In case this configuration option is defined, then the root IMFS does not support making files (no support for `mknod()`).

NOTES:

  None.

## 24.14.14. CONFIGURE_IMFS_DISABLE_MKNOD_DEVICE

CONSTANT:

  `CONFIGURE_IMFS_DISABLE_MKNOD_DEVICE`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the root IMFS supports making device files.

DESCRIPTION:

  In case this configuration option is defined, then the root IMFS does not support making device files.

NOTES:

  None.

## 24.14.15. CONFIGURE_IMFS_DISABLE_MKNOD_FILE

CONSTANT:

  `CONFIGURE_IMFS_DISABLE_MKNOD_FILE`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the root IMFS supports making regular files.

DESCRIPTION:

  In case this configuration option is defined, then the root IMFS does not support making regular files.

NOTES:

  None.

## 24.14.16. CONFIGURE_IMFS_DISABLE_MOUNT

CONSTANT:

  `CONFIGURE_IMFS_DISABLE_MOUNT`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the root IMFS supports mounting other filesystems.

DESCRIPTION:

  In case this configuration option is defined, then the root IMFS does not support mounting other filesystems (no support for `mount()`).

NOTES:

  None.

## 24.14.17. CONFIGURE_IMFS_DISABLE_READDIR

CONSTANT:

  `CONFIGURE_IMFS_DISABLE_READDIR`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the root IMFS supports reading directories.

DESCRIPTION:

  In case this configuration option is defined, then the root IMFS does not support reading directories (no support for `readdir()`). It is still possible to open files in a directory.

NOTES:

  None.

## 24.14.18. CONFIGURE_IMFS_DISABLE_READLINK

CONSTANT:

  `CONFIGURE_IMFS_DISABLE_READLINK`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the root IMFS supports reading symbolic links.

DESCRIPTION:

  In case this configuration option is defined, then the root IMFS does not support reading symbolic links (no support for `readlink()`).

NOTES:

  None.

## 24.14.19. CONFIGURE_IMFS_DISABLE_RENAME

CONSTANT:

  `CONFIGURE_IMFS_DISABLE_RENAME`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the root IMFS supports renaming files.

DESCRIPTION:

  In case this configuration option is defined, then the root IMFS does not support renaming files (no support for `rename()`).

NOTES:

  None.

## 24.14.20. CONFIGURE_IMFS_DISABLE_RMNOD

CONSTANT:

  `CONFIGURE_IMFS_DISABLE_RMNOD`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the root IMFS supports removing files.

DESCRIPTION:

  In case this configuration option is defined, then the root IMFS does not support removing files (no support for `rmnod()`).

NOTES:

  None.

## 24.14.21. CONFIGURE_IMFS_DISABLE_SYMLINK

CONSTANT:

  `CONFIGURE_IMFS_DISABLE_SYMLINK`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the root IMFS supports creating symbolic links.

DESCRIPTION:

  In case this configuration option is defined, then the root IMFS does not support creating symbolic links (no support for `symlink()`).

NOTES:

  None.

## 24.14.22. CONFIGURE_IMFS_DISABLE_UNMOUNT

CONSTANT:

  `CONFIGURE_IMFS_DISABLE_UNMOUNT`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the root IMFS supports unmounting other filesystems.

DESCRIPTION:

  In case this configuration option is defined, then the root IMFS does not support unmounting other filesystems (no support for `unmount()`).

NOTES:

  None.

## 24.14.23. CONFIGURE_IMFS_DISABLE_UTIME

CONSTANT:

  `CONFIGURE_IMFS_DISABLE_UTIME`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the root IMFS supports changing file times.

DESCRIPTION:

  In case this configuration option is defined, then the root IMFS does not support changing file times (no support for `utime()`).

NOTES:

  None.

## 24.14.24. CONFIGURE_IMFS_ENABLE_MKFIFO

CONSTANT:

  `CONFIGURE_IMFS_ENABLE_MKFIFO`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the root IMFS does not support making FIFOs (no support for `mkfifo()`).

DESCRIPTION:

  In case this configuration option is defined, then the root IMFS supports making FIFOs.

NOTES:

  None.

## 24.14.25. CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK

CONSTANT:

  `CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK`

OPTION TYPE:

  This configuration option is an integer define.

DEFAULT VALUE:

  The default value is 128.

VALUE CONSTRAINTS:

  The value of this configuration option shall be an element of {16, 32, 64, 128, 256, 512}.

DESCRIPTION:

  The value of this configuration option defines the block size for in-memory files managed by the IMFS.

NOTES:

  The configured block size has two impacts. The first is the average amount of unused memory in the last block of each file. For example, when the block size is 512, on average one-half of the last block of each file will remain unused and the memory is wasted. In contrast, when the block size is 16, the average unused memory per file is only 8 bytes. However, it requires more allocations for the same size file and thus more overhead per block for the dynamic memory management.

  Second, the block size has an impact on the maximum size file that can be stored in the IMFS. With smaller block size, the maximum file size is correspondingly smaller. The following shows the maximum file size possible based on the configured block size:

  - when the block size is 16 bytes, the maximum file size is 1,328 bytes.

  - when the block size is 32 bytes, the maximum file size is 18,656 bytes.

  - when the block size is 64 bytes, the maximum file size is 279,488 bytes.

  - when the block size is 128 bytes, the maximum file size is 4,329,344 bytes.

  - when the block size is 256 bytes, the maximum file size is 68,173,568 bytes.

  - when the block size is 512 bytes, the maximum file size is 1,082,195,456 bytes.

## 24.14.26. CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM

CONSTANT:

  `CONFIGURE_USE_DEVFS_AS_BASE_FILESYSTEM`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then an IMFS with a reduced feature set will be the base filesystem (also known as root filesystem).

NOTES:

  In case this configuration option is defined, then the following configuration options will be defined as well

  - CONFIGURE_IMFS_DISABLE_CHMOD,

  - CONFIGURE_IMFS_DISABLE_CHOWN,

  - CONFIGURE_IMFS_DISABLE_LINK,

  - CONFIGURE_IMFS_DISABLE_MKNOD_FILE,

  - CONFIGURE_IMFS_DISABLE_MOUNT,

  - CONFIGURE_IMFS_DISABLE_READDIR,

  - CONFIGURE_IMFS_DISABLE_READLINK,

  - CONFIGURE_IMFS_DISABLE_RENAME,

  - CONFIGURE_IMFS_DISABLE_RMNOD,

  - CONFIGURE_IMFS_DISABLE_SYMLINK,

  - CONFIGURE_IMFS_DISABLE_UTIME, and

  - CONFIGURE_IMFS_DISABLE_UNMOUNT.

  In addition, a simplified path evaluation is enabled. It allows only a look up of absolute paths.

  This configuration of the IMFS is basically a device-only filesystem. It is comparable in functionality to the pseudo-filesystem name space provided before RTEMS release 4.5.0.

## 24.14.27. CONFIGURE_USE_MINIIMFS_AS_BASE_FILESYSTEM

CONSTANT:

  `CONFIGURE_USE_MINIIMFS_AS_BASE_FILESYSTEM`

OPTION TYPE:

  This configuration option is a boolean feature define.

DEFAULT CONFIGURATION:

  If this configuration option is undefined, then the described feature is not enabled.

DESCRIPTION:

  In case this configuration option is defined, then an IMFS with a reduced feature set will be the base filesystem (also known as root filesystem).

NOTES:

  In case this configuration option is defined, then the following configuration options will be defined as well

  - CONFIGURE_IMFS_DISABLE_CHMOD,

  - CONFIGURE_IMFS_DISABLE_CHOWN,

  - CONFIGURE_IMFS_DISABLE_LINK,

  - CONFIGURE_IMFS_DISABLE_READLINK,

  - CONFIGURE_IMFS_DISABLE_RENAME,

  - CONFIGURE_IMFS_DISABLE_SYMLINK,

  - CONFIGURE_IMFS_DISABLE_UTIME, and

  - CONFIGURE_IMFS_DISABLE_UNMOUNT.