NAME
df - report free disk space
SYNOPSIS
df [-k][-P|-t][file...]
DESCRIPTION
The df 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 the
number of free file slots, or inodes, available; when -t is specified,
the output shall contain the total allocated space as well.
OPTIONS
The df utility shall conform to the Base Definitions volume of
IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
The following options shall be supported:
-k Use 1024-byte units, instead of the default 512-byte units, when
writing space figures.
-P Produce output in the format described in the STDOUT section.
-t Include total allocated-space figures in the output.
OPERANDS
The following operand shall be supported:
file 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. Otherwise, df shall write the amount
of free space in the file system containing the specified file
operand.
STDIN
Not used.
INPUT FILES
None.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of df:
LANG Provide a default value for the internationalization variables
that are unset or null. (See the Base Definitions volume of
IEEE Std 1003.1-2001, Section 8.2, Internationalization
Variables for the precedence of internationalization variables
used to determine the values of locale categories.)
LC_ALL If set to a non-empty string value, override the values of all
the other internationalization variables.
LC_CTYPE
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).
LC_MESSAGES
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.
NLSPATH
Determine the location of message catalogs for the processing of
LC_MESSAGES .
ASYNCHRONOUS EVENTS
Default.
STDOUT
When both the -k and -P 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
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
(1024-byte when -k 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 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 -t is used.
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
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.
EXAMPLES
1. The following example writes portable information about the /usr
file system:
df -P /usr
2. Assuming that /usr/src is part of the /usr file system, the
following produces the same output as the previous example:
df -P /usr/src
RATIONALE
The behavior of df with the -P option is the default action of the 4.2
BSD df utility. The uppercase -P was selected to avoid collision with a
known industry extension using -p.
Historical df 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 ( -P) to provide information in a portable
format.
The use of 512-byte units is historical practice and maintains
compatibility with ls and other utilities in this volume of
IEEE Std 1003.1-2001. This does not mandate that the file system itself
be based on 512-byte blocks. The -k 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 -k option to switch to 1024-byte units was a good compromise.
Users who prefer the more logical 1024-byte quantity can easily alias
df to df -k without breaking many historical scripts relying on the
512-byte units.
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.
FUTURE DIRECTIONS
None.
SEE ALSO
find
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 http://www.opengroup.org/unix/online.html .