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df(P) df(P)
NAME
df - report free disk space
SYNOPSIS
df [-k][-P|-t][file...]<img src="../images/opt-end.gif"
alt="[Option End]" border="0">
DESCRIPTION
The df utility shall write the amount of available space
<img src="../images/opt-start.gif" alt="[Option Start]"
border="0"> and file slots for file systems on which
the invoking user has appropriate read access. File sys-
tems 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, avail-
able; 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 out-
put.
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, International-
ization Variables for the precedence of interna-
tionalization 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 mes-
sages 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 fol-
lowing 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 informa-
tion 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 implementa-
tion-defined format.
<total space>
The total size of the file system in 512-byte
units. The exact meaning of this figure is imple-
mentation-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 fig-
ure 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 inte-
ger, with any fractional result causing it to be rounded
to the next highest integer.
<file system root>
The directory below which the file system hierar-
chy 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
The following example writes portable information about
the /usr file system:
df -P /usr
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 exten-
sion 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 for-
mat.
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 man-
date 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 his-
torical 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 compro-
mise. Users who prefer the more logical 1024-byte quan-
tity 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 utili-
ties be modified to access a BLOCKSIZE environment vari-
able 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 Operat-
ing System Interface (POSIX), The Open Group Base Speci-
fications Issue 6, Copyright (C) 2001-2003 by the Insti-
tute 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.open-
group.org/unix/online.html .
POSIX 2003 df(P)
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