du

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. 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. Write the files sizes in units of 1024 bytes, rather than the default 512-byte units. Instead of the default output, report only the total sum for each of the specified files. 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. Provide a default value for the internationalization variables that are unset or null. (See XBD Internationalization Variables for the precedence of internationalization variables used to determine the values of locale categories.) If set to a non-empty string value, override the values of all the other internationalization variables. Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error. [XSI) ] ![[Option Start]]( Determine the location of message catalogs for the processing of LC MESSAGES. ![[Option End]]( 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 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 c