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du — estimate file space usage
du [−a|−s] [−kx] [−H|−L] [file...]
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.
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
−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
−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
−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
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.
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
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
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.
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>
The standard error shall be used only for diagnostic messages.
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
CONSEQUENCES OF ERRORS
The following sections are informative.
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
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.
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