DU(1P) POSIX Programmer's Manual DU(1P)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.
NAMEdu - estimate file space usage
SYNOPSISdu [-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 spec‐
ified 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
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 speci‐
fied 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 encoun‐
tered 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
IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari‐
ables 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 compati‐
bility 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 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 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 inaccura‐
cies 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 posi‐
tion 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 lan‐
guage 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 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 possi‐
ble 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 original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 DU(1P)
