df is as specified in the SUS but with the variations listed in the Differences section below, and as follows.
Disk space is shown in 1K blocks by default, unless the environment variable POSIXLY_CORRECT is set, in which case 512-byte blocks are used.
If an argument is the absolute file name of a disk device node containing a mounted filesystem, df shows the space available on that filesystem rather than on the filesystem containing the device node (which is always the root filesystem).
includes filesystems having 0 blocks.
uses SIZE-byte blocks.
prints sizes in human-readable format (e.g., 1K, 234M, 2G).
prints sizes in human-readable format, but uses powers of 1000 (not 1024).
lists inode information instead of block usage.
limits listing to local filesystems.
is like --block-size=1048576
does not invoke sync before getting usage info. (default)
uses the POSIX output format.
invokes sync before getting usage info.
has implementation-dependent behavior.
is same as -P as specified in the SUS.
invokes sync before getting usage info.
limits listing to filesystems of type TYPE. (Different from behavior as specified in the SUS.)
prints filesystem type.
limits listing to filesystems not of type TYPE.