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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. 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 POSIX.1‐2008, 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
                 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.1‐2008, 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.1‐2008. 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.1‐2008 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

       None.

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition,
       Standard  for  Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers,  Inc
       and  The  Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/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 .