Section: POSIX Programmer's Manual (1P)
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.
--- 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
operands; when none are specified, information shall be written for all
file systems. The format of the default output from
is unspecified, but all space figures are reported in 512-byte units,
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
is specified, the output shall contain the total allocated space as well.
utility shall conform to the Base Definitions volume of POSIX.1-2017,
, 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 section.
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
is specified, the results are unspecified. If the
operand names a file other than a special file containing a file
shall write the amount of free space in the file system containing the
shall write the amount of free space in that file system.
The following environment variables shall affect the execution of
Provide a default value for the internationalization variables that are
unset or null. (See the Base Definitions volume of POSIX.1-2017,
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
When both the
options are specified, the following header line shall be written (in
the POSIX locale):
"Filesystem 1024-blocks Used Available Capacity Mounted on\n"
option is specified without the
option, the following header line shall be written (in the POSIX
"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
The remaining output with
shall consist of one line of information for each specified
file system. These lines shall be formatted as follows:
"%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
is specified) shall be rounded up to the next higher unit. The fields
- <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 fraction:
<space used>/( <space used>+ <space free>)
expressed as a percentage. This percentage may be greater than 100 if
<space free> 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
The standard error shall be used only for diagnostic messages.
The following exit values shall be returned:
An error occurred.
CONSEQUENCES OF ERRORS
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
df -P /usr
is part of the
file system, the following produces the same output as the previous
df -P /usr/src
The behavior of
option is the default action of the 4.2 BSD
utility. The uppercase
was selected to avoid collision with a known industry extension using
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
to provide information in a portable format.
The use of 512-byte units is historical practice and maintains
and other utilities in this volume of POSIX.1-2017. 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 the mixed
512/1024-byte usage on BSD systems), and that a
option to switch to 1024-byte units was a good compromise. Users who
prefer the more logical 1024-byte quantity can easily alias
without breaking many historical scripts relying on the 512-byte
It was suggested that
and the various related utilities be modified to access a
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.1-2017,
Chapter 8, Environment Variables,
Section 12.2, Utility Syntax Guidelines
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
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
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