14.1 df: Report file system disk space usage

df reports the amount of disk space used and available on file systems. Synopsis:

     df [option]... [file]...

With no arguments, df reports the space used and available on all currently mounted file systems (of all types). Otherwise, df reports on the file system containing each argument file.

Normally the disk space is printed in units of 1024 bytes, but this can be overridden (see Block size). Non-integer quantities are rounded up to the next higher unit.

For bind mounts and without arguments, df only outputs the statistics for that device with the shortest mount point name in the list of file systems (mtab), i.e., it hides duplicate entries, unless the -a option is specified.

With the same logic, df elides a mount entry of a dummy pseude device if there is another mount entry of a real block device for that mount point with the same device number, e.g. the early-boot pseudo file system ‘rootfs’ is not shown per default when already the real root device has been mounted.

If an argument file is a disk device file containing a mounted file system, df shows the space available on that file system rather than on the file system containing the device node (i.e., the root file system). GNU df does not attempt to determine the disk usage on unmounted file systems, because on most kinds of systems doing so requires extremely nonportable intimate knowledge of file system structures.

The program accepts the following options. Also see Common options.

‘-a’

‘--all’

Include in the listing dummy file systems, which are omitted by default. Such file systems are typically special-purpose pseudo-file-systems, such as automounter entries.

‘-B size’

‘--block-size=size’

Scale sizes by size before printing them (see Block size). For example, -BG prints sizes in units of 1,073,741,824 bytes.

‘--total’

Print a grand total of all arguments after all arguments have been processed. This can be used to find out the total disk size, usage and available space of all listed devices.

For the grand total line, df prints ‘"total"’ into the source column, and ‘"-"’ into the target column. If there is no source column (see --output), then df prints ‘"total"’ into the target column, if present.

‘-h’

‘--human-readable’

Append a size letter to each size, such as ‘M’ for mebibytes. Powers of 1024 are used, not 1000; ‘M’ stands for 1,048,576 bytes. This option is equivalent to --block-size=human-readable. Use the --si option if you prefer powers of 1000.

‘-H’

Equivalent to --si.

‘-i’

‘--inodes’

List inode usage information instead of block usage. An inode (short for index node) contains information about a file such as its owner, permissions, timestamps, and location on the disk.

‘-k’

Print sizes in 1024-byte blocks, overriding the default block size (see Block size). This option is equivalent to --block-size=1K.

‘-l’

‘--local’

Limit the listing to local file systems. By default, remote file systems are also listed.

‘--no-sync’

Do not invoke the sync system call before getting any usage data. This may make df run significantly faster on systems with many disks, but on some systems (notably SunOS) the results may be slightly out of date. This is the default.

‘--output’

‘--output[=field_list]’

Use the output format defined by field_list, or print all fields if field_list is omitted. In the latter case, the order of the columns conforms to the order of the field descriptions below.

The use of the --output together with each of the options -i, -P, and -T is mutually exclusive.

FIELD_LIST is a comma-separated list of columns to be included in df's output and therefore effectively controls the order of output columns. Each field can thus be used at the place of choice, but yet must only be used once.

Valid field names in the field_list are:

‘source’

The source of the mount point, usually a device.

‘fstype’

File system type.

‘itotal’

Total number of inodes.

‘iused’

Number of used inodes.

‘iavail’

Number of available inodes.

‘ipcent’

Percentage of iused divided by itotal.

‘size’

Total number of blocks.

‘used’

Number of used blocks.

‘avail’

Number of available blocks.

‘pcent’

Percentage of used divided by size.

‘target’

The mount point.

The fields for block and inodes statistics are affected by the scaling options like -h as usual.

The definition of the field_list can even be splitted among several --output uses.

          #!/bin/sh
          # Print the TARGET (i.e., the mount point) along with their percentage
          # statistic regarding the blocks and the inodes.
          df --out=target --output=pcent,ipcent
          
          # Print all available fields.
          df --o

‘-P’

‘--portability’

Use the POSIX output format. This is like the default format except for the following:

1. The information about each file system is always printed on exactly one line; a mount device is never put on a line by itself. This means that if the mount device name is more than 20 characters long (e.g., for some network mounts), the columns are misaligned.
2. The labels in the header output line are changed to conform to POSIX.
3. The default block size and output format are unaffected by the DF_BLOCK_SIZE, BLOCK_SIZE and BLOCKSIZE environment variables. However, the default block size is still affected by POSIXLY_CORRECT: it is 512 if POSIXLY_CORRECT is set, 1024 otherwise. See Block size.

‘--si’

Append an SI-style abbreviation to each size, such as ‘M’ for megabytes. Powers of 1000 are used, not 1024; ‘M’ stands for 1,000,000 bytes. This option is equivalent to --block-size=si. Use the -h or --human-readable option if you prefer powers of 1024.

‘--sync’

Invoke the sync system call before getting any usage data. On some systems (notably SunOS), doing this yields more up to date results, but in general this option makes df much slower, especially when there are many or very busy file systems.

‘-t fstype’

‘--type=fstype’

Limit the listing to file systems of type fstype. Multiple file system types can be specified by giving multiple -t options. By default, nothing is omitted.

‘-T’

‘--print-type’

Print each file system's type. The types printed here are the same ones you can include or exclude with -t and -x. The particular types printed are whatever is supported by the system. Here are some of the common names (this list is certainly not exhaustive):

‘nfs’

An NFS file system, i.e., one mounted over a network from another machine. This is the one type name which seems to be used uniformly by all systems.

‘4.2, ufs, efs...’

A file system on a locally-mounted hard disk. (The system might even support more than one type here; Linux does.)

‘hsfs, cdfs’

A file system on a CD-ROM drive. HP-UX uses ‘cdfs’, most other systems use ‘hsfs’ (‘hs’ for “High Sierra”).

‘pcfs’

An MS-DOS file system, usually on a diskette.

‘-x fstype’

‘--exclude-type=fstype’

Limit the listing to file systems not of type fstype. Multiple file system types can be eliminated by giving multiple -x options. By default, no file system types are omitted.

‘-v’

Ignored; for compatibility with System V versions of df.

An exit status of zero indicates success, and a nonzero value indicates failure. Failure includes the case where no output is generated, so you can inspect the exit status of a command like ‘df -t ext3 -t reiserfs dir’ to test whether dir is on a file system of type ‘ext3’ or ‘reiserfs’.

Since the list of file systems (mtab) is needed to determine the file system type, failure includes the cases when that list cannot be read and one or more of the options -a, -l, -t or -x is used together with a file name argument.