df (Unix)

Df ( / usr / bin / df) stands for disk free and is a system program on UNIX and UNIX -like operating systems, with the degree of filling of mounted file systems can be queried. It is standardized by the POSIX standard as well as the Single Unix Specification.

Df was already part of the AT & T UNIX Version 1, that is one of the oldest generation of Unix system programs. The GNU implementation of df, their behavior, however, differs significantly from the POSIX standard, is one of the GNU core utilities.


A typical command line utility df gives its output to stdout, error messages to stderr. The argument is a pathname can be specified. But not the latter has a FIFO, a simple file, a directory or a disk device representing device file, so the results are not defined. Otherwise, the information of that file system is output, containing the specified file. If no path name is specified, all mounted file systems are listed.

The example shows the output from an AIX system, the specified device is mounted there by default to / home:

# Df / dev/hd1 File System 512 blocks Free % Used Iused % Iused Mounted on / dev/hd1 2097152 167 772 92 % 7255 8% / home The output is by default in typical Unix file systems blocks ( units of 512 bytes ), plus the utilization of inodes is displayed. Because each file takes at least an inode, a file system can also be full if still free blocks available, but all inodes are in use, which is why this information is essential for the administrator. About the Switch - k can also be displayed in kilobytes (1024 bytes).

Notes on use

POSIX Switch

The exact output is not specified in the POSIX standard, and therefore differs in various Unix derivatives. However, POSIX defines the switch -P, which causes accurately specified output format, which can to portable scripts that are to run on many Unix platforms, fall back.

Special case of HP- Ux

The output of the HP- Ux implementation of df differs significantly from that of other systems. A much more obvious on the familiar issue, the HP - Ux- bdf command.