Df (Unix)
standard Unix computer program
df is a shell command for reporting the amount of available and consumed storage space on a file system.
Although df is short for disk free, the command is not limited to disk storage. It was developed during the long period of time when disk-based storage was the ubiquitous mass storage technology.
The Single Unix Specification (SUS) specifies that space is reported in blocks of 512 bytes, and that at a minimum, it reports the file system names and the amount of free space. Using 512-bytes as the unit of measure is a historical practice and maintains compatibility with ls and other commands. Notably, the file system need not be constrained to internally use 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 use alias to map df to df -k without breaking many historical scripts relying on the 512-byte units.
The command first appeared in Version 1 AT&T Unix.
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This entry incorporates text from “Df (Unix)” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.