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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
du — estimate file space usage
SYNOPSIS
du [-a|-s] [-kx] [-H|-L] [file...]
DESCRIPTION
By default, the du utility shall write to standard output 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 directories, it shall report an error condition and the
final exit status is affected. A file that occurs multiple times under one file operand and that has a
link count greater than 1 shall be counted and written for only one entry. It is implementation-defined
whether a file that has a link count no greater than 1 is counted and written just once, or is counted
and written for each occurrence. It is implementation-defined whether a file that occurs under one file
operand is counted for other file operands. 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 POSIX.1‐2017, 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. The -a option shall not affect whether non-
directories given as file operands are 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
specified 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 written. If no file is specified, the current
directory 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 internationalization variables that are unset or null. (See the
Base Definitions volume of POSIX.1‐2017, 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.
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 POSIX.1‐2017. 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 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 written 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 Application cannot use that combination.
The -a and -s options were adopted from the SVID except that the System V behavior of not listing non-
directories 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 messages) was considered counter-intuitive,
and thus it was specified that the POSIX Shell and Utilities default behavior shall be to produce such
messages. These messages can be turned off with shell redirection to achieve the System V behavior.
The -x option is historical practice on recent BSD systems. It has been adopted by this volume of
POSIX.1‐2017 because there was no other historical 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
A future version of this standard may require that a file that occurs multiple times shall be counted and
written for only one entry, even if the occurrences are under different file operands.
SEE ALSO
ls
The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment Variables, Section 12.2, Utility
Syntax Guidelines
The System Interfaces volume of POSIX.1‐2017, fstatat()
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .
Any typographical or formatting errors that appear in this page are most likely to have been introduced
during the conversion of the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 DU(1POSIX)