df (1p) - Linux Manuals
df: report free disk space
PROLOG
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.NAME
df - report free disk space
SYNOPSIS
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,
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:
The following operand shall be supported:
The following environment variables shall affect the execution of
df:
When both the -k and -P options are specified, the following
header line shall be written (in the POSIX
locale):
When the -P option is specified without the -k option,
the following header line shall be written (in the POSIX
locale):
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:
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:
The name of the file system, in an implementation-defined format.
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:
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.
The directory below which the file system hierarchy appears.
The output format is unspecified when -t is used.
The standard error shall be used only for diagnostic messages.
The following exit values shall be returned:
Default.
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 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.
OPTIONS
OPERANDS
STDIN
INPUT FILES
ENVIRONMENT VARIABLES
ASYNCHRONOUS EVENTS
STDOUT
"Filesystem 1024-blocks Used Available Capacity Mounted on\n"
"Filesystem 512-blocks Used Available Capacity Mounted on\n"
"%s %d %d %d %d%% %s\n", <file system name>, <total space>,
<space used>, <space free>, <percentage used>,
<file system root>
<space used>/( <space used>+ <space free>)
STDERR
OUTPUT FILES
EXTENDED DESCRIPTION
EXIT STATUS
CONSEQUENCES OF ERRORS
APPLICATION USAGE
EXAMPLES
df -P /usr
df -P /usr/src
RATIONALE
FUTURE DIRECTIONS
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 .