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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

       df — report free disk space

SYNOPSIS

       df [−k] [−P|−t] [file...]

DESCRIPTION

       The  df  utility  shall  write the amount of available space and file slots for file systems on which the
       invoking user has appropriate read access. File systems shall be specified by  the  file  operands;  when
       none  are  specified, information shall be written for all file systems. The format of the default output
       from df is unspecified, but all space figures are reported in 512-byte units, unless  the  −k  option  is
       specified. This output shall contain at least the file system names, amount of available space on each of
       these  file  systems,  and,  if no options other than −t are specified, the number of free file slots, or
       inodes, available; when −t is specified, the output shall contain the total allocated space as well.

OPTIONS

       The df utility shall conform to the Base Definitions volume of POSIX.1‐2008, Section 12.2, Utility Syntax
       Guidelines.

       The following options shall be supported:

       −k        Use 1024-byte units, instead of the default 512-byte units, when writing space figures.

       −P        Produce output in the format described in the STDOUT section.

       −t        Include total allocated-space figures in the output.

OPERANDS

       The following operand shall be supported:

       file      A pathname of a file within the hierarchy of the desired file system.  If a file other  than  a
                 FIFO,  a  regular  file,  a directory, or a special file representing the device containing the
                 file system (for example, /dev/dsk/0s1) is specified, the results are unspecified. If the  file
                 operand  names  a  file  other than a special file containing a file system, df shall write the
                 amount of free space in the file system containing the specified file operand.   Otherwise,  df
                 shall write the amount of free space in that file system.

STDIN

       Not used.

INPUT FILES

       None.

ENVIRONMENT VARIABLES

       The following environment variables shall affect the execution of df:

       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 and informative messages written to standard output.

       NLSPATH   Determine the location of message catalogs for the processing of LC_MESSAGES.

ASYNCHRONOUS EVENTS

       Default.

STDOUT

       When both the −k and −P options are specified, the following header line shall be written (in  the  POSIX
       locale):

           "Filesystem 1024-blocks Used Available Capacity Mounted on\n"

       When the −P option is specified without the −k option, the following header line shall be written (in the
       POSIX locale):

           "Filesystem 512-blocks Used Available Capacity Mounted on\n"

       The  implementation  may  adjust the spacing of the header line and the individual data lines so that the
       information is presented in orderly columns.

       The remaining output with −P shall consist of one line of information for  each  specified  file  system.
       These lines shall be formatted as follows:

           "%s %d %d %d %d%% %s\n", <file system name>, <total space>,
               <space used>, <space free>, <percentage used>,
               <file system root>

       In  the following list, all quantities expressed in 512-byte units (1024-byte when −k is specified) shall
       be rounded up to the next higher unit. The fields are:

       <file system name>
                 The name of the file system, in an implementation-defined format.

       <total space>
                 The total size of the file system in 512-byte units.  The  exact  meaning  of  this  figure  is
                 implementation-defined,  but should include <space used>, <space free>, plus any space reserved
                 by the system not normally available to a user.

       <space used>
                 The total amount of space allocated to existing files in the file system, in 512-byte units.

       <space free>
                 The total amount of space available within the file system for the creation  of  new  files  by
                 unprivileged users, in 512-byte units. When this figure is less than or equal to zero, it shall
                 not  be  possible  to  create  any  new files on the file system without first deleting others,
                 unless the process has appropriate privileges. The figure written may be less than zero.

       <percentage used>
                 The percentage of the normally available space that is currently allocated to all files on  the
                 file system. This shall be calculated using the fraction:

                     <space used>/( <space used>+ <space free>)

                 expressed as a percentage. This percentage may be greater than 100 if <space free> is less than
                 zero. The percentage value shall be expressed as a positive integer, with any fractional result
                 causing it to be rounded to the next highest integer.

       <file system root>
                 The directory below which the file system hierarchy appears.

       The output format is unspecified when −t is used.

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

       On most systems, the ``name of the file system, in an implementation-defined format'' is the special file
       on which the file system is mounted.

       On large file systems, the calculation specified for percentage used can create huge rounding errors.

EXAMPLES

        1. The following example writes portable information about the /usr file system:

               df −P /usr

        2. Assuming that /usr/src is part of the /usr file system, the following produces the same output as the
           previous example:

               df −P /usr/src

RATIONALE

The behavior of df with the −P option is the default action of the 4.2 BSD df utility. The uppercase −P
was selected to avoid collision with a known industry extension using −p.

Historical df implementations vary considerably in their default output. It was therefore necessary to
describe the default output in a loose manner to accommodate all known historical implementations and to
add a portable option (−P) to provide information in a portable format.

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 more logical 1024-byte quantity can easily alias df to df −k
without breaking many historical scripts relying on the 512-byte units.

It was suggested that df and the various related utilities be modified to access a BLOCKSIZE environment
variable to achieve consistency and user acceptance. Since this is not historical practice on any system,
it is left as a possible area for system extensions and will be re-evaluated in a future version if it is
widely implemented.

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 .

IEEE/The Open Group                                   2013                                            DF(1POSIX)