Df (Unix)

' (abbreviation for disk f"'ree") is a standard Unix command used to display the amount of available disk space for file systems on which the invoking user has appropriate read access. is typically implemented using the statfs or statvfs system calls.
History.
 for Unix-like systems is part of the X/Open Portability Guide since issue 2 of 1987. It was inherited into the first version of POSIX and the Single Unix Specification. It first appeared in Version 1 AT&T Unix.
The version of bundled in GNU coreutils was written by Torbjorn Granlund, David MacKenzie, and Paul Eggert.
Usage.
The Single UNIX Specification specifications for are:
 df [-k] [-P|-t] [-del] [file...]
Most Unix and Unix-like operating systems add extra options. The BSD and GNU coreutils versions include , where free space is listed in human readable format, adding units with the appropriate SI prefix (e.g. 10 MB), , listing inode usage, and , restricting display to only local filesystems. GNU includes as well, listing filesystem type information, but the GNU shows the sizes in 1K blocks by default.
Specification.
The Single Unix Specification (SUS) specifies by original space is reported in blocks of 512 bytes, and that at a minimum, the file system names and the amount of free space.
The use of 512-byte units is historical practice and maintains compatibility with and other utilities. This does not mandate that the file system itself be based on 512-byte blocks. The 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 option to switch to 1024-byte units was a good compromise. Users who prefer the more logical 1024-byte quantity can easily to without breaking many historical scripts relying on the 512-byte units.
The output with shall consist of one line of information for each specified file system. These lines shall be formatted as follows:
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:
Example.
Example outputs of the df command:
$ df
Filesystem 1K-blocks Used Available Use% Mounted on
udev 48764976 0 48764976 0% /dev
tmpfs 9757068 173100 9583968 2% /run
/dev/sda2 1824504008 723009800 1008791744 42% /
tmpfs 48785328 0 48785328 0% /dev/shm
tmpfs 5120 0 5120 0% /run/lock
tmpfs 48785328 0 48785328 0% /sys/fs/cgroup
/dev/sda1 523248 3672 519576 1% /boot/efi
$ df -i
Filesystem Inodes IUsed IFree IUse% Mounted on
udev 12191244 500 12190744 1% /dev
tmpfs 12196332 702 12195630 1% /run
/dev/sda2 115859456 2583820 113275636 3% /
tmpfs 12196332 1 12196331 1% /dev/shm
tmpfs 12196332 5 12196327 1% /run/lock
tmpfs 12196332 16 12196316 1% /sys/fs/cgroup
/dev/sda1 0 0 0 - /boot/efi
$ df -h
Filesystem Size Used Avail Use% Mounted on
udev 47G 0 47G 0% /dev
tmpfs 9.4G 170M 9.2G 2% /run
/dev/sda2 1.7T 690G 963G 42% /
tmpfs 47G 0 47G 0% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 47G 0 47G 0% /sys/fs/cgroup
/dev/sda1 511M 3.6M 508M 1% /boot/efi