This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding Linux
manual page for details of Linux behavior), or the interface may not be
implemented on Linux.
df — report free disk space
df [−k] [−P|−t] [file...]
utility shall write the amount of available space and file slots
for file systems on which the invoking user has appropriate read access. File
systems shall be specified by the file
operands; when none are
specified, information shall be written for all file systems. The format of
the default output from df
is unspecified, but all space figures are
reported in 512-byte units, unless the −k
option is specified.
This output shall contain at least the file system names, amount of available
space on each of these file systems, and, if no options other than
are specified, the number of free file slots, or
s, available; when −t
is specified, the output shall
contain the total allocated space as well.
utility shall conform to the Base Definitions volume of
POSIX.1‐2008, Section 12.2
, Utility Syntax Guidelines
The following options shall be supported:
- Use 1024-byte units, instead of the default 512-byte units,
when writing space figures.
- Produce output in the format described in the STDOUT
- Include total allocated-space figures in the output.
The following operand shall be supported:
- A pathname of a file within the hierarchy of the desired
file system. If a file other than a FIFO, a regular file, a directory, or
a special file representing the device containing the file system (for
example, /dev/dsk/0s1) is specified, the results are unspecified.
If the file operand names a file other than a special file
containing a file system, df shall write the amount of free space
in the file system containing the specified file operand.
Otherwise, df shall write the amount of free space in that file
The following environment variables shall affect the execution of df
- Provide a default value for the internationalization
variables that are unset or null. (See the Base Definitions volume of
POSIX.1‐2008, Section 8.2, Internationalization
Variables for the precedence of internationalization variables used to
determine the values of locale categories.)
- If set to a non-empty string value, override the values of
all the other internationalization variables.
- Determine the locale for the interpretation of sequences of
bytes of text data as characters (for example, single-byte as opposed to
multi-byte characters in arguments).
Determine the locale that should be used to affect the format and contents
of diagnostic messages written to standard error and informative messages
written to standard output.
- Determine the location of message catalogs for the
processing of LC_MESSAGES.
When both the −k
options are specified, the
following header line shall be written (in the POSIX locale):
"Filesystem 1024-blocks Used Available Capacity Mounted on\n"
When the −P
option is specified without the −k
option, the following header line shall be written (in the POSIX locale):
"Filesystem 512-blocks Used Available Capacity Mounted on\n"
The implementation may adjust the spacing of the header line and the individual
data lines so that the information is presented in orderly columns.
The remaining output with −P
shall consist of one line of
information for each specified file system. These lines shall be formatted as
"%s %d %d %d %d%% %s\n", <file system name>, <total space>,
< space used>, <space free>, <percentage used>,
< file system root>
In the following list, all quantities expressed in 512-byte units (1024-byte
is specified) shall be rounded up to the next higher
unit. The fields are:
- <file system name>
The name of the file system, in an implementation-defined format.
- <total space>
- The total size of the file system in 512-byte units. The
exact meaning of this figure is implementation-defined, but should include
< space used>, <space free>, plus
any space reserved by the system not normally available to a user.
- <space used>
- The total amount of space allocated to existing files in
the file system, in 512-byte units.
- <space free>
- The total amount of space available within the file system
for the creation of new files by unprivileged users, in 512-byte units.
When this figure is less than or equal to zero, it shall not be possible
to create any new files on the file system without first deleting others,
unless the process has appropriate privileges. The figure written may be
less than zero.
- <percentage used>
The percentage of the normally available space that is currently allocated
to all files on the file system. This shall be calculated using the
<space used>/( <space used>+ <space free>)
expressed as a percentage. This percentage may be greater than 100 if <
> is less than zero. The percentage value shall be
expressed as a positive integer, with any fractional result causing it to be
rounded to the next highest integer.
- <file system root>
The directory below which the file system hierarchy appears.
The output format is unspecified when −t
The standard error shall be used only for diagnostic messages.
The following exit values shall be returned:
- Successful completion.
- An error occurred.
The following sections are informative.
On most systems, the ``name of the file system, in an implementation-defined
format'' is the special file on which the file system is mounted.
On large file systems, the calculation specified for percentage used can create
huge rounding errors.
- The following example writes portable information about the
/usr file system:
- Assuming that /usr/src is part of the /usr
file system, the following produces the same output as the previous
The behavior of df
with the −P
option is the default action
of the 4.2 BSD df
utility. The uppercase −P
to avoid collision with a known industry extension using −p
implementations vary considerably in their default output.
It was therefore necessary to describe the default output in a loose manner to
accommodate all known historical implementations and to add a portable option
) to provide information in a portable format.
The use of 512-byte units is historical practice and maintains compatibility
and other utilities in this volume of POSIX.1‐2008. This
does not mandate that the file system itself be based on 512-byte blocks. The
option was added as a compromise measure. It was agreed by
the standard developers that 512 bytes was the best default unit because of
its complete historical consistency on System V ( versus
512/1024-byte usage on BSD systems), and that a −k
switch to 1024-byte units was a good compromise. Users who prefer the more
logical 1024-byte quantity can easily alias df
without breaking many historical scripts relying on the
It was suggested that df
and the various related utilities be modified to
access a BLOCKSIZE
environment variable to achieve consistency and user
acceptance. Since this is not historical practice on any system, it is left as
a possible area for system extensions and will be re-evaluated in a future
version if it is widely implemented.
The Base Definitions volume of POSIX.1‐2008, Chapter 8
, Section 12.2
, Utility Syntax
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
7, Copyright (C) 2013 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013
Technical Corrigendum 1 applied.) In the event of any discrepancy between this
version and the original IEEE and The Open Group Standard, the original IEEE
and The Open Group Standard is the referee document. The original Standard can
be obtained online at http://www.unix.org/online.html .
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