Build a FAT filesystem image (QNX)


mkfatfsimg [option...] [buildfile] [directory] [outputfile]

mkxfs -t fatfsimg [option...] [buildfile] [directory] [outputfile]

Runs on:

Linux, Microsoft Windows


Treat undeclared intermediate directories as errors. If there's a target filesystem entry of /x/y, and /x has never occurred explicitly in the buildfile, the patch file, the input directory, or as a child of a recursively included directory, then /x is considered an undeclared intermediate directory.
Display warnings for undeclared intermediate directories.
-l inputline
("el") Process inputline before interpreting the buildfile. Input lines given to mkfatfsimg should be quoted to prevent interpretation by the shell. Multiple -l options are processed in the order specified. This option is especially useful for setting global attributes when the input is a directory only.
Don't use timestamps in the files. Using the -n option permits identical images in binary format. One n strips timestamps from files that vary from run to run. More than one strips ALL time information, which is necessary on Windows NTFS with daylight saving time.
-o directory
("oh") Specify a directory to be used for all permanent build artifacts, other than the output image itself.
-p patchfile
Apply patching instructions from this file (see "Patch files," below).
-r root
Search the default paths in this directory before the default.
Operate verbosely. Specifying additional v options increases the verbosity. The default is quiet operation.


The mkfatfsimg utility reads a text buildfile and/or a specified directory and produces a binary image file containing a FAT ( filesystem created from the given input. You can copy this file to target media at a later stage.

Note: Don't confuse this command with mkdosfs, which initializes an empty FAT filesystem and is available for Neutrino hosts only.

You specify the input and output on the command line:

The filename of the buildfile that describes the contents of the FAT filesystem; use a hyphen (-) to specify standard input (the default).
The root of a directory hierarchy to be appended to the file list specified in buildfile (if any). The default is no directory.
The filename of the image file containing the FAT filesystem; use a hyphen (-) to specify standard output (the default). Note that you can specify the output file only if you specified at least either a buildfile or a directory.

If you don't specify either a buildfile or a directory, a buildfile is expected as input from standard input. The output is always an image file; if you don't specify outputfile, image-file data will be produced on standard output.

This utility supports long filenames (VFAT).

By default, the FAT type (12, 16, or 32) is derived from the volume size and other geometry parameters. You can use the fat attribute to override this.

  • The FAT filesystem supports only file sizes less than 4 GB.
  • There's only very limited support for permissions in FAT filesystems. A file or directory can be flagged as "read-only"; mkfatfsimg sets this flag when it encounters a file or directory without write permissions for anybody.
  • There's no support for hard or symbolic links in FAT filesystems. If you explicitly add a file link or implicitly include one as part of a directory in your buildfile, mkfatfsimg either prints a warning and skips the item or prints an error and exits in failure, depending on the optional attribute setting.
  • FAT filesystems have no concept of ownership. If you use the uid or gid attribute in the buildfile, it's silently ignored.


The mkfatfsimg command uses the same buildfile grammar as mkifs, but supports a different set of attributes. The buildfile is basically just a list of files that you want to be included in the FAT image file when it's built by mkfatfsimg. As well as identifying the files to be included, you can specify various attributes that are used to set parameters of the filesystem and the files in it. For example, you can specify the maximum size of the filesystem, or make individual files read-only.

Note: You can't use a backslash (\) to break long lines into smaller pieces.

In a buildfile, a pound sign (#) indicates a comment; anything between it and the end of the line is ignored. There must be a space between a buildfile command and the pound sign.

Each line is in the form:

[attributes] file_specification

where the attributes (with the enclosing square brackets) and the file specification are both optional.

You can use an attribute:

Attributes provide information about the file following the attribute. They are enclosed in square brackets; when combining attributes (e.g., to specify the search path on the host system and declare the file as mandatory), enclose both attribute tokens in the same pair of square brackets. For example:

# correct way
[search=/tmp -optional] filename
# incorrect way
[search=/tmp] [-optional] filename

There are two types of attributes:

Boolean attributes
Those prefixed with a plus (+) or minus (-) sign.
Value attributes
Those ending with an equals sign (=) followed by a value. Don't put any spaces around the equals sign.

A question mark (?) before an attribute makes the setting conditional. The attribute is set only if it hasn't already been set. For example:


sets the +followlink attribute only if +followlink or -followlink hasn't already been set.

The file_specification takes one of the following forms:

The file is copied from the host to the location in the image defined by the prefix attribute. If path isn't absolute, mkfatfsimg looks for it in the locations identified by the search attribute.
The specified file or contents of the specified directory are fetched from the host filesystem and placed into the image.
An inline definition. The contents of the file are listed within the buildfile itself, enclosed in braces ({ })—the file doesn't exist on the host system anywhere. The contents of the inline file can't be on the same line as the opening or closing brace.
Note: The mkfatfsimg utility doesn't parse the contents of an inline file for anything but the closing brace. For example, mkfatfsimg doesn't interpret a pound sign (#) in an inline file as the beginning of a comment. The syntax of the inline file depends on what it's used for on the target system.

Closing braces (}) and backslashes (\) in an inline file must be escaped with a backslash.

You can enclose a filename in double quotes (") if it includes spaces or unusual characters.


In mkfatfsimg buildfiles, the following attributes are supported:

The following attributes are recognized, but not semantically supported by mkfatfsimg:

The following attributes are recognized, but are only partly supported by mkfatfsimg:

Since the default values will generate only a 1,44MB FAT12 image, you should explicitly specify at least the image size by specifying num_sectors, to make sure that the image produced will be large enough to hold all specified files and that it will be compatible with your specific target device.

An OR-bar indicates that either the first element or the second element must be present, but not both (e.g., +|-followlink means either +followlink or -followlink, but not +-followlink).

cd attribute


Set the current working directory to the specified pathname before attempting to open the host file. The default is the directory from which you invoked mkfatfsimg.

dperms attribute


Set the access permissions of the directory. The dperms_spec can be one of the following:

The default dperms_spec is *.

Note that FAT filesystems don't support permissions; they have only a read-only attribute. If the combination of permissions indicates that the directory should not be writeable for anyone, then the read-only attribute is set.

fat attribute


Set the FAT type of the target filesystem. The type must be one of 12, 16, or 32. Note that by defining a specific target FAT type, you may limit the parameter choices so far that no valid filesystem can be constructed. It's usually best to leave this as the default, which is to auto-determine a reasonable FAT type. See the sec_per_clus attribute for how this works.

filter attribute


Run the host file through the filter program specified, presenting the host file data as standard input to the program and using the standard output from the program as the data to be placed into the FAT filesystem. Default is no filter. You can specify a filter_spec of none. This is useful if you need to override a global filter specification.


Whether to resolve any symbolic file links and include the target files instead of the links.

If you specify +followlink or omit the attribute, whenever an item taken from the host filesystem is a symbolic file link, mkfatfsimg follows the link and includes its target. If you specify -followlink, the resulting behavior depends on how the optional attribute is set. If it's enabled (+optional), mkfatfsimg displays a warning and skips the file; if it's disabled (-optional), the utility prints an error and exits with a failure code.

Note: The followlink attribute does not apply to symbolic directory links that are explicitly named in the buildfile. Those links will always be resolved and the contents of the target directories will be included recursively. For directory links included indirectly as part of an explicitly named parent directory, they will not be followed, and the resulting behavior again depends on the setting for optional.

gid attribute


This attribute is supposed to set the group ID number for the file. Since FAT filesystems have no provision to store file ownership information, this attribute is silently disregarded.

media attribute


Specify a media indicator code. The default value is 0xF8.

mountperms attribute

This attribute is supposed to set the access permissions for the filesystem mountpoint. Since the FAT filesystem has no provision to store mount information, this attribute is silently disregarded.

mtime attribute


Set the timestamps of the files or directories to the specified time. The time_spec must be either:

Timestamps specified with the mtime attribute aren't affected by the -n option.

num_sectors attribute


Set the number of 512-byte sectors on the volume. The size_spec is an integer, optionally followed by K, M, or G (the case doesn't matter). The default value is 2880.

optional attribute (boolean)


If true, and the host file can't be found, output a warning and continue building the embedded filesystem. If false, and the host file can't be found, output an error message and exit mkfatfsimg. The default is true.

perms attribute


Set the access permissions of the file. The perms_spec can be one of the following:

The default perms_spec is *.

Note that FAT filesystems don't support permissions; they have only a read-only attribute. If the combination of permissions indicates that the file should not be writeable for anyone, then the read-only attribute is set.

prefix attribute


Set the prefix on the target file names. The default is the empty string.


This attribute specifies that mkfatfsimg should search for the file in the named locations on the host system. The search directory portion of the host file name isn't included in the name that's stored in the FAT filesystem. Colon separators and forward slashes in the paths are the standard Unix conventions, but for Windows searches, you must use the standard Windows conventions, such as semicolon separators and backslashes in the paths.

sec_per_clus attribute


Define the number of sectors assigned per each cluster. This must be one of 1, 2, 4, 8, 16, 32, or 64. Note that while "officially" allowed, you can't choose a value of 128 because it would necessarily result in a cluster size > 32K and would likely be incompatible with many systems.

The default is to auto-detect a reasonable sectors/cluster ratio. The built-in algorithm tries to use as few sectors per cluster as possible and use the smallest-possible FAT type. This strategy is meant to minimize allocation overhead (the average over-allocation is 1/2 cluster per each file). Of course, small clusters will go along with large FATs which also take up some space. If you know that your filesystem will contain only few files, you may choose a larger sectors/cluster ratio to keep the FATs smaller.

sector_size attribute


Specify the sector size of the filesystem's target device. The size_spec is an integer, optionally followed by k (the case doesn't matter). The default value is 512; valid values are 512, 1k, 2k, 4k, 8k, 16k, and 32k. Note that any sector size greater than 4k may be incompatible with some operating systems and will cause a warning to be issued.

type attribute

Sets the type of the file being created in the FAT filesystem. Allowable types are:
  • file—a regular, everyday file (the default)
  • dir—a directory
Note: You don't need to specify the type when you're copying the contents of a directory. For example, this command:
creates an empty directory named /usr/bin, with the same owner and permissions as for the host directory. To recursively copy /usr/nto/x86/bin to /usr/bin, you just need to specify:

Note that link is an accepted type, but because FAT filesystems don't support symbolic links, you shouldn't use this setting with mkfatfsimg. If you do, it either prints a warning message (if +optional is specified), or prints an error message and exits in failure (if -optional is specified).

uid attribute


This attribute is supposed to set the user ID number for the file. Since FAT filesystems have no provision to store file ownership information, this attribute is silently disregarded.

vol_lbl attribute


Set the volume label to the given string. The default is no label.

Patch files

Patch files let you override the user ID, group ID, and permissions of certain files, depending on their location and filename pattern. Patches are applied after all files have been collected (from the buildfile and/or the specified directory). Consequently, patch files can override settings specified in the buildfile.

Patch files must contain only lines of the form:




In comment lines, # must be the first character. The entire line is treated as a comment and is ignored.

The type is either d or f, optionally followed by r. Type d patches are applied only to directories, and type f patches are applied only to files. An r indicates that the patch should be applied recursively within path; without r, the patch is applied to path only.

The pattern is a filename pattern that specifies which files to apply the patch to. The uid and gid must be decimal numbers, while perms must be an octal number (see chmod). Note that it isn't possible to set only the user ID, group ID, or permissions; for each match, all three are affected. As mentioned above, the FAT filesystem ignores any settings for the user ID and group ID.


Here's a sample buildfile, my_fatfs.bld:

# A sample buildfile for mkfatfsimg

In this example, we've specified a sector count of 512*1024, which relates to an image size of 128 MB. The files and subdirectories from the /home/thaupt directory on the host system are to be recursively copied into the root directory of the FAT filesystem. To create a FAT filesystem image file using above buildfile, invoke mkfatfsimg as follows:

mkfatfsimg my_fatfs.bld my_fatfs.img

This creates the my_fatfs.img file containing the FAT filesystem, which you could then copy to a target system's hard-disk partition as follows:

dd if=my_fatfs.img of=/dev/hd0t7 count=524288

Exit status:

Successful completion.
An error occurred.