RM(1) BSD Reference Manual RM(1)
rm - remove directory entries
rm [-f | -i] [-dPRrv] file ...
The rm utility attempts to remove the non-directory type files specified on the command line. If the permissions of the file do not permit writ- ing, and the standard input device is a terminal, the user is prompted (on the standard error output) for confirmation. The options are as follows: -d Attempt to remove directories as well as other types of files. -f Attempt to remove the files without prompting for confirmation, regardless of the file's permissions. If the file does not exist, do not display a diagnostic message or modify the exit status to reflect an error. The -f option overrides any previous -i op- tions. -i Request confirmation before attempting to remove each file, re- gardless of the file's permissions, or whether or not the stan- dard input device is a terminal. The -i option overrides any pre- vious -f options. -P Overwrite regular files before deleting them. Files are overwrit- ten three times, first with the byte pattern 0xAA, then 0x55, and then with random data, before they are deleted. Some care is tak- en to ensure that the data are actually written to disk, but this cannot be guaranteed, even on traditional filesystems; on log- structured filesystems or if any block-journaling scheme is in use, this option is completely useless. If the file cannot be overwritten, it will not be removed. Files with multiple links will not be overwritten. If the -f op- tion is given, they will still be removed, otherwise, they will remain untouched. Entries are renamed to the basename "rm.XXXXXXXX" (where 'X' are generated randomly) within the same parent directory before re- moving, if the length of the generated total pathname will not overflow the buffer. This prevents recovery of (almost) all basenames as well. -R Attempt to remove the file hierarchy rooted in each file argu- ment. The -R option implies the -d option. If the -i option is specified, the user is prompted for confirmation before each directory's contents are processed (as well as before the attempt is made to remove the directory). If the user does not respond affirmatively, the file hierarchy rooted in that directory is skipped. -r Equivalent to -R. -v Cause rm to be verbose, showing files as they are processed. The rm utility removes symbolic links, not the files referenced by the links. It is an error to attempt to remove the files "." or "..". It is forbid- den to remove the file ".." merely to avoid the antisocial consequences of inadvertently doing something like "rm -r .*". The rm utility exits 0 if all of the named files or file hierarchies were removed, or if the -f option was specified and all of the existing files or file hierarchies were removed. If an error occurs, rm exits with a value >0.
Recursively remove all files contained within the foobar directory hierarchy: $ rm -rf foobar rm uses getopt(3) standard argument processing. Removing filenames that begin with a dash (e.g., -file) in the current directory which might oth- erwise be taken as option flags to rm can be accomplished as follows: rm -- -file or rm ./-file
rmdir(1), unlink(2), arc4random(3), fts(3), getopt(3), symlink(7)
The rm utility differs from historical implementations in that the -f op- tion only masks attempts to remove non-existent files instead of masking a large variety of errors. Also, historical BSD implementations prompted on the standard output, not the standard error output. The interactive mode used to be a dsw command, a carryover from the an- cient past with an amusing etymology. The rm utility is almost IEEE Std 1003.2 ("POSIX.2") compatible, except that POSIX requires rm to act like rmdir(1) when the file specified is a directory. This implementation requires the -d option if such behavior is desired. This follows the historical behavior of rm with respect to directories. The -v option is an extension. The -P option attempts to conform to U.S. DoD 5220-22.M, "National Indus- trial Security Program Operating Manual" ("NISPOM") as updated by Change 2 and the July 23, 2003 "Clearing & Sanitization Matrix". However, unlike earlier revisions of NISPOM, the 2003 matrix imposes requirements which make it clear that the standard does not and can not apply to the erasure of individual files, in particular requirements relating to spare sector management for an entire magnetic disk. Because these requirements are not met, the -P option does not conform to the standard.
An rm command appeared in Version 1 AT&T UNIX. Modification of the -P option to overwrite with random content and rename entries to random filenames before removal appeared in MirOS #10.
The -P option assumes that the underlying file system is a fixed-block file system. FFS is a fixed-block file system, LFS is not. In addition, only regular files are overwritten, other types of files are not. Recent research indicates that as many as 35 overwrite passes with carefully chosen data patterns may be necessary to actually prevent recovery of data from a magnetic disk. Thus the -P option is likely both insufficient for its design purpose and far too costly for default operation. However, it will at least prevent the recovery of data from FFS volumes with fsdb(8). MirOS BSD #10-current January 17, 2009 2
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