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

DF(P)				    POSIX Programmer's Manual				    DF(P)

       df - report free disk space

       df [-k][-P|-t][file...]

       The  df utility shall write the amount of available space    and file slots  for file sys-
       tems on which the invoking user has appropriate read access. File systems shall be  speci-
       fied  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  fig-
       ures  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  the number of free file slots, or inodes, available; when -t is specified,
       the output shall contain the total allocated space as well.

       The df 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:

       -k     Use 1024-byte units, instead of the default 512-byte units, when writing space fig-

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

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

       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.	Otherwise, df shall write the amount of free space in the
	      file system containing the specified file operand.

       Not used.


       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 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.

	      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-

	      Determine the locale that should be used to affect the format and contents of diag-
	      nostic messages written to standard error and informative messages written to stan-
	      dard output.

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


       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 fig-
	      ure 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  frac-
       tional 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.

       The standard error shall be used only for diagnostic messages.



       The following exit values shall be returned:

	0     Successful completion.

       >0     An error occurred.


       The following sections are informative.

       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.

	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

       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  his-
       torical	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 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 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 BLOCK-
       SIZE 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.



       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					    DF(P)

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