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du(P) du(P)
NAME
du - estimate file space usage
SYNOPSIS
du [-a | -s][-kx][-H | -L][file ...]
DESCRIPTION
By default, the du utility shall write to standard out-
put the size of the file space allocated to, and the
size of the file space allocated to each subdirectory
of, the file hierarchy rooted in each of the specified
files. By default, when a symbolic link is encountered
on the command line or in the file hierarchy, du shall
count the size of the symbolic link (rather than the
file referenced by the link), and shall not follow the
link to another portion of the file hierarchy. The size
of the file space allocated to a file of type directory
shall be defined as the sum total of space allocated to
all files in the file hierarchy rooted in the directory
plus the space allocated to the directory itself.
When du cannot stat() files or stat() or read directo-
ries, it shall report an error condition and the final
exit status is affected. Files with multiple links shall
be counted and written for only one entry. The directory
entry that is selected in the report is unspecified. By
default, file sizes shall be written in 512-byte units,
rounded up to the next 512-byte unit.
OPTIONS
The du 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:
-a In addition to the default output, report the
size of each file not of type directory in the
file hierarchy rooted in the specified file.
Regardless of the presence of the -a option, non-
directories given as file operands shall always
be listed.
-H If a symbolic link is specified on the command
line, du shall count the size of the file or file
hierarchy referenced by the link.
-k Write the files sizes in units of 1024 bytes,
rather than the default 512-byte units.
-L If a symbolic link is specified on the command
line or encountered during the traversal of a
file hierarchy, du shall count the size of the
file or file hierarchy referenced by the link.
-s Instead of the default output, report only the
total sum for each of the specified files.
-x When evaluating file sizes, evaluate only those
files that have the same device as the file spec-
ified by the file operand.
Specifying more than one of the mutually-exclusive
options -H and -L shall not be considered an error. The
last option specified shall determine the behavior of
the utility.
OPERANDS
The following operand shall be supported:
file The pathname of a file whose size is to be writ-
ten. If no file is specified, the current direc-
tory shall be used.
STDIN
Not used.
INPUT FILES
None.
ENVIRONMENT VARIABLES
The following environment variables shall affect the
execution of du:
LANG Provide a default value for the internationaliza-
tion 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 cate-
gories.)
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.
NLSPATH
Determine the location of message catalogs for
the processing of LC_MESSAGES .
ASYNCHRONOUS EVENTS
Default.
STDOUT
The output from du shall consist of the amount of space
allocated to a file and the name of the file, in the
following format:
"%d %s\n", <size>, <pathname>
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
None.
EXAMPLES
None.
RATIONALE
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 1024-byte quantity can easily
alias du to du -k without breaking the many historical
scripts relying on the 512-byte units.
The -b option was added to an early proposal to provide
a resolution to the situation where System V and BSD
systems give figures for file sizes in blocks, which is
an implementation-defined concept. (In common usage, the
block size is 512 bytes for System V and 1024 bytes for
BSD systems.) However, -b was later deleted, since the
default was eventually decided as 512-byte units.
Historical file systems provided no way to obtain exact
figures for the space allocation given to files. There
are two known areas of inaccuracies in historical file
systems: cases of indirect blocks being used by the file
system or sparse files yielding incorrectly high values.
An indirect block is space used by the file system in
the storage of the file, but that need not be counted in
the space allocated to the file. A sparse file is one in
which an lseek() call has been made to a position beyond
the end of the file and data has subsequently been writ-
ten at that point. A file system need not allocate all
the intervening zero-filled blocks to such a file. It is
up to the implementation to define exactly how accurate
its methods are.
The -a and -s options were mutually-exclusive in the
original version of du. The POSIX Shell and Utilities
description is implied by the language in the SVID where
-s is described as causing "only the grand total" to be
reported. Some systems may produce output for -sa, but
a Strictly Conforming POSIX Shell and Utilities Applica-
tion cannot use that combination.
The -a and -s options were adopted from the SVID except
that the System V behavior of not listing non-directo-
ries explicitly given as operands, unless the -a option
is specified, was considered a bug; the BSD-based
behavior (report for all operands) is mandated. The
default behavior of du in the SVID with regard to
reporting the failure to read files (it produces no mes-
sages) was considered counter-intuitive, and thus it was
specified that the POSIX Shell and Utilities default
behavior shall be to produce such messages. These mes-
sages can be turned off with shell redirection to
achieve the System V behavior.
The -x option is historical practice on recent BSD sys-
tems. It has been adopted by this volume of
IEEE Std 1003.1-2001 because there was no other histori-
cal method of limiting the du search to a single file
hierarchy. This limitation of the search is necessary to
make it possible to obtain file space usage information
about a file system on which other file systems are
mounted, without having to resort to a lengthy find and
awk script.
FUTURE DIRECTIONS
None.
SEE ALSO
ls , the System Interfaces volume of
IEEE Std 1003.1-2001, stat()
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 du(P)
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