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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 .