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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.

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 .