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Linux 2.6 - man page for du (linux section 1posix)

DU(P)				    POSIX Programmer's Manual				    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 output the size of the file space allo-
       cated to, and the size of the file space allocated to each subdirectory of, the file hier-
       archy  rooted  in each of the specified files. By default, when a symbolic link is encoun-
       tered on the command line or in the file hierarchy, du shall count the size  of	the  sym-
       bolic 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 condi-
       tion 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 unspeci-
       fied.  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,  Sec-
       tion 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 direc-
	      tory 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 tra-
	      versal 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 consid-
       ered 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 IEEE Std 1003.1-2001, Section 8.2, Inter-
	      nationalization 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  interna-
	      tionalization 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  argu-
	      ments).

       LC_MESSAGES
	      Determine the locale that should be used to affect the format and contents of diag-
	      nostic 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 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 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 imple-
       mentation-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 eventu-
       ally 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  incor-
       rectly  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 out-
       put  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 mes-
       sages 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  IEEE Std 1003.1-2001  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.

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 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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					    DU(P)


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