     [file version.texi not included]

     START-INFO-DIR-ENTRY
     * File utilities: (fileutils).  GNU file utilities.
     * chgrp: (fileutils)chgrp invocation.           Change file groups.
     * chown: (fileutils)chown invocation.           Change file owners/groups.
     * chmod: (fileutils)chmod invocation.           Change file permissions.
     * cp: (fileutils)cp invocation.                 Copy files.
     * dd: (fileutils)dd invocation.                 Copy and convert a file.
     * df: (fileutils)df invocation.                 Report filesystem disk usage.
     * dir: (fileutils)dir invocation.               List directories briefly.
     * dircolors: (fileutils)dircolors invocation.   Color setup for ls.
     * du: (fileutils)du invocation.                 Report on disk usage.
     * install: (fileutils)install invocation.       Copy and change attributes.
     * ln: (fileutils)ln invocation.                 Make links between files.
     * ls: (fileutils)ls invocation.                 List directory contents.
     * mkdir: (fileutils)mkdir invocation.           Create directories.
     * mkfifo: (fileutils)mkfifo invocation.         Create FIFOs (named pipes).
     * mknod: (fileutils)mknod invocation.           Create special files.
     * mv: (fileutils)mv invocation.                 Rename files.
     * rm: (fileutils)rm invocation.                 Remove files.
     * rmdir: (fileutils)rmdir invocation.           Remove empty directories.
     * shred: (fileutils)shred invocation.           Remove files more securely.
     * sync: (fileutils)sync invocation.             Synchronize memory and disk.
     * touch: (fileutils)touch invocation.           Change file timestamps.
     * vdir: (fileutils)vdir invocation.             List directories verbosely.
     END-INFO-DIR-ENTRY

This file documents the GNU set of file utilities.

Copyright 1994, 95, 96, 1999, 2001 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License''.

GNU file utilities
******************

This manual documents version VERSION of the GNU file utilities.

Introduction
************

This manual is incomplete: No attempt is made to explain basic file concepts in a way suitable for novices.  Thus, if you are interested, please get involved in improving this manual.  The entire GNU community will benefit.

The GNU file utilities are mostly compatible with the POSIX.2 standard.

Please report bugs to bug-fileutils@gnu.org.  Remember to include the version number, machine architecture, input files, and any other information needed to reproduce the bug: your input, what you expected, what you got, and why it is wrong.  Diffs are welcome, but please include a description of the problem as well, since this is sometimes difficult to infer. See Bugs (GNU CC).

This manual was originally derived from the Unix man pages in the distribution, which were written by David MacKenzie and updated by Jim Meyering.  What you are reading now is the authoritative documentation for these utilities;  the man pages are no longer being maintained. François Pinard did the initial conversion to Texinfo format. Karl Berry did the indexing, some reorganization, and editing of the results. Richard Stallman contributed his usual invaluable insights to the overall process.

Common options
**************

Certain options are available in all of these programs (in fact, every GNU program should accept them).  Rather than writing identical descriptions for each of the programs, they are described here.

--help
     Print a usage message listing all available options, then exit successfully.

--version
     Print the version number, then exit successfully.

Backup options
==============

Some GNU programs (at least cp, install, ln, and mv) optionally make backups of files before writing new versions. These options control the details of these backups.  The options are also briefly mentioned in the descriptions of the particular programs.

-b
--backup[=METHOD]
     Make a backup of each file that would otherwise be overwritten or removed. Without this option, the original versions are destroyed. Use METHOD to determine the type of backups to make. When this option is used but METHOD is not specified, then the value of the VERSION_CONTROL environment variable is used.  And if VERSION_CONTROL is not set, the default backup type is existing.

     Note that the short form of this option, -b does not accept any argument.  Using -b is equivalent to using --backup=existing.

     This option corresponds to the Emacs variable version-control; the values for METHOD are the same as those used in Emacs. This option also accepts more descriptive names. The valid METHODs are (unique abbreviations are accepted):

     none
     off
          Never make backups.

     numbered
     t
          Always make numbered backups.

     existing
     nil
          Make numbered backups of files that already have them, simple backups of the others.

     simple
     never
          Always make simple backups.  Please note never is not to be confused with none.

-S SUFFIX
--suffix=SUFFIX
     Append SUFFIX to each backup file made with -b.  If this option is not specified, the value of the SIMPLE_BACKUP_SUFFIX environment variable is used.  And if SIMPLE_BACKUP_SUFFIX is not set, the default is ~, just as in Emacs.

--version-control=METHOD
     This option is obsolete and will be removed in a future release. It has been replaced with --backup.

Block size
==========

Some GNU programs (at least df, du, and ls) display file sizes in ``blocks''.  You can adjust the block size to make file sizes easier to read.  The block size used for display is independent of any filesystem block size.

Normally, disk usage sizes are rounded up, disk free space sizes are rounded down, and other sizes are rounded to the nearest value with ties rounding to an even value.

The default block size is chosen by examining the following environment variables in turn; the first one that is set determines the block size.

DF_BLOCK_SIZE
     This specifies the default block size for the df command. Similarly, DU_BLOCK_SIZE specifies the default for du and LS_BLOCK_SIZE for ls.

BLOCK_SIZE
     This specifies the default block size for all three commands, if the above command-specific environment variables are not set.

POSIXLY_CORRECT
     If neither the COMMAND_BLOCK_SIZE nor the BLOCK_SIZE variables are set, but this variable is set, the block size defaults to 512.

If none of the above environment variables are set, the block size currently defaults to 1024 bytes, but this number may change in the future.

A block size specification can be a positive integer specifying the number of bytes per block, or it can be human-readable or si to select a human-readable format.

With human-readable formats, output sizes are followed by a size letter such as M for megabytes.  BLOCK_SIZE=human-readable uses powers of 1024; M stands for 1,048,576 bytes. BLOCK_SIZE=si is similar, but uses powers of 1000; M stands for 1,000,000 bytes.  (SI, the International System of Units, defines these power-of-1000 prefixes.)

An integer block size can be followed by a size letter to specify a multiple of that size.  When this notation is used, the size letters normally stand for powers of 1024, and can be followed by an optional B for ``byte''; but if followed by D (for ``decimal byte''), they stand for powers of 1000.  For example, BLOCK_SIZE=4MB is equivalent to BLOCK_SIZE=4194304, and BLOCK_SIZE=4MD is equivalent to BLOCK_SIZE=4000000.

The following size letters are defined.  Large sizes like 1Y may be rejected by your computer due to limitations of its arithmetic.

k
     kilo: 2^10 = 1024 for human-readable, or 10^3 = 1000 for si.

M
     Mega: 2^20 = 1,048,576 or 10^6 = 1,000,000.

G
     Giga: 2^30 = 1,073,741,824 or 10^9 = 1,000,000,000.

T
     Tera: 2^40 = 1,099,511,627,776 or 10^12 = 1,000,000,000,000.

P
     Peta: 2^50 = 1,125,899,906,842,624 or 10^15 = 1,000,000,000,000,000.

E
     Exa: 2^60 = 1,152,921,504,606,846,976 or 10^18 = 1,000,000,000,000,000,000.

Z
     Zetta: 2^70 = 1,180,591,620,717,411,303,424 or 10^21 = 1,000,000,000,000,000,000,000.

Y
     Yotta: 2^80 = 1,208,925,819,614,629,174,706,176 or 10^24 = 1,000,000,000,000,000,000,000,000.

Block size defaults can be overridden by an explicit --block-size=SIZE option.  The -k or --kilobytes option is equivalent to --block-size=1k, which is the default unless the POSIXLY_CORRECT environment variable is set.  The -h or --human-readable option is equivalent to --block-size=human-readable.  The --si option is equivalent to --block-size=si.

Target directory
================

Some GNU programs (at least cp, install, ln, and mv) allow you to specify the target directory via this option:

--target-directory=DIRECTORY
     Specify the destination DIRECTORY.

     The interface for most programs is that after processing options and a finite (possibly zero) number of fixed-position arguments, the remaining argument list is either expected to be empty, or is a list of items (usually files) that will all be handled identically.  The xargs program is designed to work well with this convention.

     The commands in the mv-family are unusual in that they take a variable number of arguments with a special case at the end (namely, the target directory).  This makes it nontrivial to perform some operations, e.g., ``move all files from here to ../d/'', because mv * ../d/ might exhaust the argument space, and ls | xargs ... doesn't have a clean way to specify an extra final argument for each invocation of the subject command.  (It can be done by going through a shell command, but that requires more human labor and brain power than it should.)

     The --target-directory option allows the cp, install, ln, and mv programs to be used conveniently with xargs.  For example, you can move the files from the current directory to a sibling directory, d like this: (However, this doesn't move files whose names begin with ..)

          ls |xargs mv --target-directory=../d

     If you use the GNU find program, you can move all files with this command:

          find . -mindepth 1 -maxdepth 1 \
            | xargs mv --target-directory=../d

     But that will fail if there are no files in the current directory or if any file has a name containing a newline character. The following example removes those limitations and requires both GNU find and GNU xargs:

          find . -mindepth 1 -maxdepth 1 -print0 \
            | xargs --null --no-run-if-empty \
                mv --target-directory=../d

Trailing slashes
================

Some GNU programs (at least cp and mv) allow you to remove any trailing slashes from each SOURCE argument before operating on it.  The --strip-trailing-slashes option enables this behavior.

This is useful when a SOURCE argument may have a trailing slash and specify a symbolic link to a directory.  This scenario is in fact rather common because some shells can automatically append a trailing slash when performing file name completion on such symbolic links.  Without this option, mv, for example, (via the system's rename function) must interpret a trailing slash as a request to dereference the symbolic link and so must rename the indirectly referenced directory and not the symbolic link.  Although it may seem surprising that such behavior be the default, it is required by POSIX.2 and is consistent with other parts of that standard.

File permissions
****************

     [file perm.texi not included]

     [file getdate.texi not included]

Directory listing
*****************

This chapter describes the ls command and its variants dir and vdir, which list information about files.

ls: List directory contents
===========================

The ls program lists information about files (of any type, including directories).  Options and file arguments can be intermixed arbitrarily, as usual.

For non-option command-line arguments that are directories, by default ls lists the contents of directories, not recursively, and omitting files with names beginning with ..  For other non-option arguments, by default ls lists just the file name.  If no non-option arguments are specified, ls lists the contents of the current directory.

By default, the output is sorted alphabetically.  If standard output is a terminal, the output is in columns (sorted vertically) and control characters are output as question marks; otherwise, the output is listed one per line and control characters are output as-is.

Because ls is such a fundamental program, it has accumulated many options over the years.  They are described in the subsections below; within each section, options are listed alphabetically (ignoring case). The division of options into the subsections is not absolute, since some options affect more than one aspect of ls's operation.

The -g option is accepted but ignored, for compatibility with Unix.  Also see Common options.

Which files are listed
----------------------

These options determine which files ls lists information for. By default, any files and the contents of any directories on the command line are shown.

-a
--all
     List all files in directories, including files that start with ..

-A
--almost-all
     List all files in directories except for . and ...

-B
--ignore-backups
     Do not list files that end with ~, unless they are given on the command line.

-d
--directory
     List just the names of directories, as with other types of files, rather than listing their contents.

-I PATTERN
--ignore=PATTERN
     Do not list files whose names match the shell pattern (not regular expression) PATTERN unless they are given on the command line.  As in the shell, an initial . in a file name does not match a wildcard at the start of PATTERN.  Sometimes it is useful to give this option several times.  For example,

          $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'

     The first option ignores names of length 3 or more that start with ., the second ignores all two-character names that start with . except .., and the third ignores names that start with #.

-L
--dereference
     In a long listing, show file information (e.g., times and permissions) for the referents of symbolic links rather than for the symbolic links themselves.

-R
--recursive
     List the contents of all directories recursively.

What information is listed
--------------------------

These options affect the information that ls displays.  By default, only file names are shown.

-D
--dired
     With the long listing (-l) format, print an additional line after the main output:

          //DIRED// BEG1 END1 BEG2 END2 ...

     The BEGN and ENDN are unsigned integers that record the byte position of the beginning and end of each file name in the output. This makes it easy for Emacs to find the names, even when they contain unusual characters such as space or newline, without fancy searching.

     If directories are being listed recursively (-R), output a similar line after each subdirectory:

          //SUBDIRED// FORMAT BEG1 END1 ...

     Finally, output a line of the form:

          //DIRED-OPTIONS// --quoting-style=WORD

     where WORD is the quoting style (see Formatting the file names).

-G
--no-group
     Inhibit display of group information in a long format directory listing. (This is the default in some non-GNU versions of ls, so we provide this option for compatibility.)

-h
--human-readable
     Append a size letter such as M for megabytes to each size. Powers of 1024 are used, not 1000; M stands for 1,048,576 bytes. Use the --si option if you prefer powers of 1000.

-H
--si
     Append a size letter such as M for megabytes to each size.  (SI is the International System of Units, which defines these letters as prefixes.)  Powers of 1000 are used, not 1024; M stands for 1,000,000 bytes.  Use the -h or --human-readable option if you prefer powers of 1024.

     Warning: the meaning of -H will change in the future to conform to POSIX.  Use --si for the old meaning.

-i
--inode
     Print the inode number (also called the file serial number and index number) of each file to the left of the file name.  (This number uniquely identifies each file within a particular filesystem.)

-l
--format=long
--format=verbose
     In addition to the name of each file, print the file type, permissions, number of hard links, owner name, group name, size in bytes, and timestamp (by default, the modification time).  For files with a time more than six months old or in the future, the timestamp contains the year instead of the time of day. If the timestamp contains today's date with the year rather than a time of day, the file's time is in the future, which means you probably have clock skew problems which may break programs like make that rely on file times.

     For each directory that is listed, preface the files with a line total BLOCKS, where BLOCKS is the total disk allocation for all files in that directory.  The block size currently defaults to 1024 bytes, but this can be overridden (see Block size). The BLOCKS computed counts each hard link separately; this is arguably a deficiency.

     The permissions listed are similar to symbolic mode specifications (see Symbolic Modes).  But ls combines multiple bits into the third character of each set of permissions as follows:

     s
          If the setuid or setgid bit and the corresponding executable bit are both set.

     S
          If the setuid or setgid bit is set but the corresponding executable bit is not set.

     t
          If the sticky bit and the other-executable bit are both set.

     T
          If the sticky bit is set but the other-executable bit is not set.

     x
          If the executable bit is set and none of the above apply.

     -
          Otherwise.

     Following the permission bits is a single character that specifies whether an alternate access method applies to the file.  When that character is a space, there is no alternate access method.  When it is a printing character (e.g., +), then there is such a method.

-o
     Produce long format directory listings, but don't display group information. It is equivalent to using --format=long with --no-group . This option is provided for compatibility with other versions of ls.

-s
--size
     Print the disk allocation of each file to the left of the file name. This is the amount of disk space used by the file, which is usually a bit more than the file's size, but it can be less if the file has holes.

     Normally the disk allocation is printed in units of 1024 bytes, but this can be overridden (see Block size).

     For files that are NFS-mounted from an HP-UX system to a BSD system, this option reports sizes that are half the correct values.  On HP-UX systems, it reports sizes that are twice the correct values for files that are NFS-mounted from BSD systems.  This is due to a flaw in HP-UX; it also affects the HP-UX ls program.

Sorting the output
------------------

These options change the order in which ls sorts the information it outputs.  By default, sorting is done by character code (e.g., ASCII order).

-c
--time=ctime
--time=status
--time=use
     If the long listing format (e.g., -l, -o) is being used, print the status change time (the ctime in the inode) instead of the modification time. When explicitly sorting by time (--sort=time or -t) or when not using a long listing format, sort according to the status change time.

-f
     Primarily, like -U---do not sort; list the files in whatever order they are stored in the directory.  But also enable -a (list all files) and disable -l, --color, and -s (if they were specified before the -f).

-r
--reverse
     Reverse whatever the sorting method is---e.g., list files in reverse alphabetical order, youngest first, smallest first, or whatever.

-S
--sort=size
     Sort by file size, largest first.

-t
--sort=time
     Sort by modification time (the mtime in the inode), newest first.

-u
--time=atime
--time=access
     If the long listing format (e.g., --format=long) is being used, print the last access time (the atime in the inode). When explicitly sorting by time (--sort=time or -t) or when not using a long listing format, sort according to the access time.

-U
--sort=none
     Do not sort; list the files in whatever order they are stored in the directory.  (Do not do any of the other unrelated things that -f does.)  This is especially useful when listing very large directories, since not doing any sorting can be noticeably faster.

-v
--sort=version
     Sort by version name and number, lowest first.  It behaves like a default sort, except that each sequence of decimal digits is treated numerically as an index/version number.  (see More details about version sort.)

-X
--sort=extension
     Sort directory contents alphabetically by file extension (characters after the last .); files with no extension are sorted first.

More details about version sort
-------------------------------

The version sort takes into account the fact that file names frequently include indices or version numbers.  Standard sorting functions usually do not produce the ordering that people expect because comparisons are made on a character-by-character basis.  The version sort addresses this problem, and is especially useful when browsing directories that contain many files with indices/version numbers in their names:

           > ls -1            > ls -1v
           foo.zml-1.gz       foo.zml-1.gz
           foo.zml-100.gz     foo.zml-2.gz
           foo.zml-12.gz      foo.zml-6.gz
           foo.zml-13.gz      foo.zml-12.gz
           foo.zml-2.gz       foo.zml-13.gz
           foo.zml-25.gz      foo.zml-25.gz
           foo.zml-6.gz       foo.zml-100.gz

Note also that numeric parts with leading zeroes are considered as fractional one:

           > ls -1            > ls -1v
           abc-1.007.tgz      abc-1.007.tgz
           abc-1.012b.tgz     abc-1.01a.tgz
           abc-1.01a.tgz      abc-1.012b.tgz

General output formatting
-------------------------

These options affect the appearance of the overall output.

-1
--format=single-column
     List one file per line.  This is the default for ls when standard output is not a terminal.

-C
--format=vertical
     List files in columns, sorted vertically.  This is the default for ls if standard output is a terminal.  It is always the default for the dir and d programs. GNU ls uses variable width columns to display as many files as possible in the fewest lines.

--color [=WHEN]
     Specify whether to use color for distinguishing file types.  WHEN may be omitted, or one of:

       * none - Do not use color at all.  This is the default.

       * auto - Only use color if standard output is a terminal.

       * always - Always use color.

     Specifying --color and no WHEN is equivalent to --color=always. Piping a colorized listing through a pager like more or less usually produces unreadable results.  However, using more -f does seem to work.

-F
--classify
--indicator-style=classify
     Append a character to each file name indicating the file type.  Also, for regular files that are executable, append *.  The file type indicators are / for directories, @ for symbolic links, | for FIFOs, = for sockets, and nothing for regular files.

--full-time
     List times in full, rather than using the standard abbreviation heuristics.  The format is currently similar to that of date, but this is planned to change in a future release, partly because modern file time stamps have more precision.  It's not possible to change the format, but you can extract out the date string with cut and then pass the result to date -d.  See date invocation (Shell utilities).

     This is most useful because the time output includes the seconds.  (Unix filesystems store file timestamps only to the nearest second, so this option shows all the information there is.)  For example, this can help when you have a Makefile that is not regenerating files properly.

--indicator-style=WORD
     Append a character indicator with style WORD to entry names, as follows:

     none
          Do not append any character indicator; this is the default.

     file-type
          Append / for directories, @ for symbolic links, | for FIFOs, = for sockets, and nothing for regular files.  This is the same as the -p or --file-type option.

     classify
          Append * for executable regular files, otherwise behave as for file-type.  This is the same as the -F or --classify option.

-k
--kilobytes
     Print file sizes in 1024-byte blocks, overriding the default block size (see Block size).

-m
--format=commas
     List files horizontally, with as many as will fit on each line, separated by ,  (a comma and a space).

-n
--numeric-uid-gid
     List the numeric UID and GID instead of the names.

-p
--file-type
--indicator-style=file-type
     Append a character to each file name indicating the file type. This is like -F, except that executables are not marked.

-x FORMAT
--format=across
--format=horizontal
     List the files in columns, sorted horizontally.

-T COLS
--tabsize=COLS
     Assume that each tabstop is COLS columns wide.  The default is 8. ls uses tabs where possible in the output, for efficiency.  If COLS is zero, do not use tabs at all.

-w
--width=COLS
     Assume the screen is COLS columns wide.  The default is taken from the terminal settings if possible; otherwise the environment variable COLUMNS is used if it is set; otherwise the default is 80.

Formatting the file names
-------------------------

These options change how file names themselves are printed.

-b
--escape
--quoting-style=escape
     Quote nongraphic characters in file names using alphabetic and octal backslash sequences like those used in C.

-N
--literal
     Do not quote file names.

-q
--hide-control-chars
     Print question marks instead of nongraphic characters in file names. This is the default if the output is a terminal and the program is ls.

-Q
--quote-name
--quoting-style=c
     Enclose file names in double quotes and quote nongraphic characters as in C.

--quoting-style=WORD
     Use style WORD to quote output names.  The WORD should be one of the following:

     literal
          Output names as-is.

     shell
          Quote names for the shell if they contain shell metacharacters or would cause ambiguous output.

     shell-always
          Quote names for the shell, even if they would normally not require quoting.

     c
          Quote names as for a C language string; this is the same as the -Q or --quote-name option.

     escape
          Quote as with c except omit the surrounding double-quote characters; this is the same as the -b or --escape option.

     clocale
          Quote as with c except use quotation marks appropriate for the locale.

     locale
          Like clocale, but quote `like this' instead of "like this" in the default C locale.  This looks nicer on many displays.

     You can specify the default value of the --quoting-style option with the environment variable QUOTING_STYLE.  If that environment variable is not set, the default value is literal, but this default may change to shell in a future version of this package.

--show-control-chars
     Print nongraphic characters as-is in file names. This is the default unless the output is a terminal and the program is ls.

dir: Briefly list directory contents
====================================

dir (also installed as d) is equivalent to ls -C -b; that is, by default files are listed in columns, sorted vertically, and special characters are represented by backslash escape sequences.

See ls.

vdir: Verbosely list directory contents
=======================================

vdir (also installed as v) is equivalent to ls -l -b; that is, by default files are listed in long format and special characters are represented by backslash escape sequences.

dircolors: Color setup for ls
=============================

dircolors outputs a sequence of shell commands to set up the terminal for color output from ls (and dir, etc.). Typical usage:

     eval `dircolors [OPTION]... [FILE]`

If FILE is specified, dircolors reads it to determine which colors to use for which file types and extensions.  Otherwise, a precompiled database is used.  For details on the format of these files, run dircolors --print-database.

The output is a shell command to set the LS_COLORS environment variable.  You can specify the shell syntax to use on the command line, or dircolors will guess it from the value of the SHELL environment variable.

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

-b
--sh
--bourne-shell
     Output Bourne shell commands.  This is the default if the SHELL environment variable is set and does not end with csh or tcsh.

-c
--csh
--c-shell
     Output C shell commands.  This is the default if SHELL ends with csh or tcsh.

-p
--print-database
     Print the (compiled-in) default color configuration database.  This output is itself a valid configuration file, and is fairly descriptive of the possibilities.

Basic operations
****************

This chapter describes the commands for basic file manipulation: copying, moving (renaming), and deleting (removing).

cp: Copy files and directories
==============================

cp copies files (or, optionally, directories).  The copy is completely independent of the original.  You can either copy one file to another, or copy arbitrarily many files to a destination directory. Synopsis:

     cp [OPTION]... SOURCE DEST
     cp [OPTION]... SOURCE... DIRECTORY

If the last argument names an existing directory, cp copies each SOURCE file into that directory (retaining the same name). Otherwise, if only two files are given, it copies the first onto the second.  It is an error if the last argument is not a directory and more than two non-option arguments are given.

Generally, files are written just as they are read.  For exceptions, see the --sparse option below.

By default, cp does not copy directories.  However, the -R, -a, and -r options cause cp to copy recursively by descending into source directories and copying files to corresponding destination directories.

By default, cp follows symbolic links only when not copying recursively.  This default can be overridden with the --no-dereference (-d), --dereference (-L), and -H options.  If more than one of these options is specified, the last one silently overrides the others.

cp generally refuses to copy a file onto itself, with the following exception: if --force --backup is specified with SOURCE and DEST identical, and referring to a regular file, cp will make a backup file, either regular or numbered, as specified in the usual ways (see Backup options).  This is useful when you simply want to make a backup of an existing file before changing it.

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

-a
--archive
     Preserve as much as possible of the structure and attributes of the original files in the copy (but do not attempt to preserve internal directory structure;  i.e., ls -U may list the entries in a copied directory in a different order). Equivalent to -dpR.

-b
--backup[=METHOD]
     See Backup options. Make a backup of each file that would otherwise be overwritten or removed. As a special case, cp makes a backup of SOURCE when the force and backup options are given and SOURCE and DEST are the same name for an existing, regular file.  One useful application of this combination of options is this tiny Bourne shell script:

          #!/bin/sh
          # Usage: backup FILE...
          # Create a GNU-style backup of each listed FILE.
          for i in "$; do
            cp --backup --force "$i" "$i"
          done

-d
--no-dereference
     Copy symbolic links as symbolic links rather than copying the files that they point to, and preserve hard links between source files in the copies.

-f
--force
     When copying without this option and an existing destination file cannot be opened for writing, the copy fails.  However, with --force), when a destination file cannot be opened, cp then unlinks it and tries to open it again.  Contrast this behavior with that enabled by --link and --symbolic-link, whereby the destination file is never opened but rather is unlinked unconditionally.  Also see the description of --remove-destination.

-H
     If a command line argument specifies a symbolic link, then copy the file it points to rather than the symbolic link itself.  However, copy (preserving its nature) any symbolic link that is encountered via recursive traversal.

-i
--interactive
     Prompt whether to overwrite existing regular destination files.

-l
--link
     Make hard links instead of copies of non-directories.

-L
--dereference
     Always follow symbolic links.

-p
--preserve
     Preserve the original files' owner, group, permissions, and timestamps. In the absence of this option, each destination file is created with the permissions of the corresponding source file, minus the bits set in the umask. See File permissions.

-P
--parents
     Form the name of each destination file by appending to the target directory a slash and the specified name of the source file.  The last argument given to cp must be the name of an existing directory. For example, the command:

          cp --parents a/b/c existing_dir

     copies the file a/b/c to existing_dir/a/b/c, creating any missing intermediate directories.

     Warning: the meaning of -P will change in the future to conform to POSIX.  Use --parents for the old meaning, and --no-dereference for the new.

-r
     Copy directories recursively, copying any non-directories and special files (e.g., symbolic links, FIFOs and device files) as if they were regular files.  This means trying to read the data in each source file and writing it to the destination.  It is usually a mistake to apply cp -r to special files like FIFOs and the ones typically found in the /dev directory.  In most cases, cp -r will hang indefinitely trying to read from FIFOs and special files like /dev/console, and it will fill up your destination disk if you use it to copy /dev/zero. Use the --recursive (-R) option instead if you want to copy special files, preserving their special nature rather than reading from them to copy their contents.

-R
--recursive
     Copy directories recursively, preserving non-directories (contrast with -r just above).

--remove-destination
     Remove each existing destination file before attempting to open it (contrast with -f above).

--sparse=WHEN
     A sparse file contains holes---a sequence of zero bytes that does not occupy any physical disk blocks; the read system call reads these as zeroes.  This can both save considerable disk space and increase speed, since many binary files contain lots of consecutive zero bytes.  By default, cp detects holes in input source files via a crude heuristic and makes the corresponding output file sparse as well.

     The WHEN value can be one of the following:

     auto
          The default behavior: the output file is sparse if the input file is sparse.

     always
          Always make the output file sparse.  This is useful when the input file resides on a filesystem that does not support sparse files (the most notable example is efs filesystems in SGI IRIX 5.3 and earlier), but the output file is on another type of filesystem.

     never
          Never make the output file sparse. This is useful in creating a file for use with the mkswap command, since such a file must not have any holes.

--strip-trailing-slashes
     Remove any trailing slashes from each SOURCE argument. See Trailing slashes.

-s
--symbolic-link
     Make symbolic links instead of copies of non-directories.  All source file names must be absolute (starting with /) unless the destination files are in the current directory.  This option merely results in an error message on systems that do not support symbolic links.

-S SUFFIX
--suffix=SUFFIX
     Append SUFFIX to each backup file made with -b. See Backup options.

--target-directory=DIRECTORY
     Specify the destination DIRECTORY. See Target directory.

-v
--verbose
     Print the name of each file before copying it.

-V METHOD
--version-control=METHOD
     Change the type of backups made with -b.  The METHOD argument can be none (or off), numbered (or t), existing (or nil), or never (or simple).  See Backup options.

-x
--one-file-system
     Skip subdirectories that are on different filesystems from the one that the copy started on. However, mount point directories are copied.

dd: Convert and copy a file
===========================

dd copies a file (from standard input to standard output, by default) with a changeable I/O block size, while optionally performing conversions on it.  Synopsis:

     dd [OPTION]...

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

The numeric-valued options below (BYTES and BLOCKS) can be followed by a multiplier: b=512, c=1, w=2, xM=M, or any of the standard block size suffixes like k=1024 (see Block size).

Use different dd invocations to use different block sizes for skipping and I/O.  For example, the following shell commands copy data in 512 kB blocks between a disk and a tape, but do not save or restore a 4 kB label at the start of the disk:

     disk=/dev/rdsk/c0t1d0s2
     tape=/dev/rmt/0

     # Copy all but the label from disk to tape.
     (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape

     # Copy from tape back to disk, but leave the disk label alone.
     (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk

if=FILE
     Read from FILE instead of standard input.

of=FILE
     Write to FILE instead of standard output.  Unless conv=notrunc is given, dd truncates FILE to zero bytes (or the size specified with seek=).

ibs=BYTES
     Read BYTES bytes at a time.

obs=BYTES
     Write BYTES bytes at a time.

bs=BYTES
     Both read and write BYTES bytes at a time.  This overrides ibs and obs.

cbs=BYTES
     Convert BYTES bytes at a time.

skip=BLOCKS
     Skip BLOCKS ibs-byte blocks in the input file before copying.

seek=BLOCKS
     Skip BLOCKS obs-byte blocks in the output file before copying.

count=BLOCKS
     Copy BLOCKS ibs-byte blocks from the input file, instead of everything until the end of the file.

conv=CONVERSION[,CONVERSION]...
     Convert the file as specified by the CONVERSION argument(s). (No spaces around any comma(s).)

     Conversions:

     ascii
          Convert EBCDIC to ASCII.

     ebcdic
          Convert ASCII to EBCDIC.

     ibm
          Convert ASCII to alternate EBCDIC.

     block
          For each line in the input, output cbs bytes, replacing the input newline with a space and padding with spaces as necessary.

     unblock
          Replace trailing spaces in each cbs-sized input block with a newline.

     lcase
          Change uppercase letters to lowercase.

     ucase
          Change lowercase letters to uppercase.

     swab
          Swap every pair of input bytes.  GNU dd, unlike others, works when an odd number of bytes are read---the last byte is simply copied (since there is nothing to swap it with).

     noerror
          Continue after read errors.

     notrunc
          Do not truncate the output file.

     sync
          Pad every input block to size of ibs with trailing zero bytes. When use with block or unblock, pad with spaces instead of zero bytes.

install: Copy files and set attributes
======================================

install copies files while setting their permission modes and, if possible, their owner and group.  Synopses:

     install [OPTION]... SOURCE DEST
     install [OPTION]... SOURCE... DIRECTORY
     install -d [OPTION]... DIRECTORY...

In the first of these, the SOURCE file is copied to the DEST target file.  In the second, each of the SOURCE files are copied to the destination DIRECTORY.  In the last, each DIRECTORY (and any missing parent directories) is created.

install is similar to cp, but allows you to control the attributes of destination files.  It is typically used in Makefiles to copy programs into their destination directories.  It refuses to copy files onto themselves.

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

-b
--backup[=METHOD]
     See Backup options. Make a backup of each file that would otherwise be overwritten or removed.

-c
     Ignored; for compatibility with old Unix versions of install.

-d
--directory
     Create each given directory and any missing parent directories, setting the owner, group and mode as given on the command line or to the defaults.  It also gives any parent directories it creates those attributes.  (This is different from the SunOS 4.x install, which gives directories that it creates the default attributes.)

-g GROUP
--group=GROUP
     Set the group ownership of installed files or directories to GROUP. The default is the process' current group.  GROUP may be either a group name or a numeric group id.

-m MODE
--mode=MODE
     Set the permissions for the installed file or directory to MODE, which can be either an octal number, or a symbolic mode as in chmod, with 0 as the point of departure (see File permissions).  The default mode is u=rwx,go=rx---read, write, and execute for the owner, and read and execute for group and other.

-o OWNER
--owner=OWNER
     If install has appropriate privileges (is run as root), set the ownership of installed files or directories to OWNER. The default is root.  OWNER may be either a user name or a numeric user ID.

-p
--preserve-timestamps
     Set the time of last access and the time of last modification of each installed file to match those of each corresponding original file. When a file is installed without this option, its last access and last modification times are both set to the time of installation. This option is useful if you want to use the last modification times of installed files to keep track of when they were last built as opposed to when they were last installed.

-s
--strip
     Strip the symbol tables from installed binary executables.

-S SUFFIX
--suffix=SUFFIX
     Append SUFFIX to each backup file made with -b. See Backup options.

--target-directory=DIRECTORY
     Specify the destination DIRECTORY. See Target directory.

-v
--verbose
     Print the name of each file before copying it.

-V METHOD
--version-control=METHOD
     Change the type of backups made with -b.  The METHOD argument can be none (or off), numbered (or t), existing (or nil), or never (or simple).  See Backup options.

mv: Move (rename) files
=======================

mv moves or renames files (or directories).  Synopsis:

     mv [OPTION]... SOURCE DEST
     mv [OPTION]... SOURCE... DIRECTORY

If the last argument names an existing directory, mv moves each other given file into a file with the same name in that directory. Otherwise, if only two files are given, it renames the first as the second.  It is an error if the last argument is not a directory and more than two files are given.

mv can move any type of file from one filesystem to another. Prior to version 4.0 of the fileutils, mv could move only regular files between filesystems. For example, now mv can move an entire directory hierarchy including special device files from one partition to another.  It first uses some of the same code that's used by cp -a to copy the requested directories and files, then (assuming the copy succeeded) it removes the originals.  If the copy fails, then the part that was copied to the destination partition is removed.  If you were to copy three directories from one partition to another and the copy of the first directory succeeded, but the second didn't, the first would be left on the destination partion and the second and third would be left on the original partition.

If a destination file exists but is normally unwritable, standard input is a terminal, and the -f or --force option is not given, mv prompts the user for whether to replace the file.  (You might own the file, or have write permission on its directory.)  If the response does not begin with y or Y, the file is skipped.

Warning: If you try to move a symlink that points to a directory, and you specify the symlink with a trailing slash, then mv doesn't move the symlink but instead moves the directory referenced by the symlink.  See Trailing slashes.

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

-b
--backup[=METHOD]
     See Backup options. Make a backup of each file that would otherwise be overwritten or removed.

-f
--force
     Do not prompt the user before removing an unwritable destination file.

-i
--interactive
     Prompt whether to overwrite each existing destination file, regardless of its permissions.  If the response does not begin with y or Y, the file is skipped.

-u
--update
     Do not move a nondirectory that has an existing destination with the same or newer modification time.

-v
--verbose
     Print the name of each file before moving it.

--strip-trailing-slashes
     Remove any trailing slashes from each SOURCE argument. See Trailing slashes.

-S SUFFIX
--suffix=SUFFIX
     Append SUFFIX to each backup file made with -b. See Backup options.

--target-directory=DIRECTORY
     Specify the destination DIRECTORY. See Target directory.

-V METHOD
--version-control=METHOD
     Change the type of backups made with -b.  The METHOD argument can be none (or off), numbered (or t), existing (or nil), or never (or simple).  See Backup options.

rm: Remove files or directories
===============================

rm removes each given FILE.  By default, it does not remove directories.  Synopsis:

     rm [OPTION]... [FILE]...

If a file is unwritable, standard input is a terminal, and the -f or --force option is not given, or the -i or --interactive option is given, rm prompts the user for whether to remove the file.  If the response does not begin with y or Y, the file is skipped.

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

-d
--directory
     Attempt to remove directories with unlink instead of rmdir, and don't require a directory to be empty before trying to unlink it.  This works only if you have appropriate privileges and if your operating system supports unlink for directories.  Because unlinking a directory causes any files in the deleted directory to become unreferenced, it is wise to fsck the filesystem after doing this.

-f
--force
     Ignore nonexistent files and never prompt the user. Ignore any previous --interactive (-i) option.

-i
--interactive
     Prompt whether to remove each file.  If the response does not begin with y or Y, the file is skipped. Ignore any previous --force (-f) option.

-r
-R
--recursive
     Remove the contents of directories recursively.

-v
--verbose
     Print the name of each file before removing it.

One common question is how to remove files whose names begin with a -.  GNU rm, like every program that uses the getopt function to parse its arguments, lets you use the -- option to indicate that all following arguments are non-options.  To remove a file called -f in the current directory, you could type either:

     rm -- -f

or:

     rm ./-f

The Unix rm program's use of a single - for this purpose predates the development of the getopt standard syntax.

shred: Remove files more securely
=================================

shred overwrites devices or files, to help prevent even very expensive hardware from recovering the data.

Ordinarily when you remove a file (see rm invocation), the data is not actually destroyed.  Only the index listing where the file is stored is destroyed, and the storage is made available for reuse. There are undelete utilities that will attempt to reconstruct the index and can bring the file back if the parts were not reused.

On a busy system with a nearly-full drive, space can get reused in a few seconds.  But there is no way to know for sure.  If you have sensitive data, you may want to be sure that recovery is not possible by actually overwriting the file with non-sensitive data.

However, even after doing that, it is possible to take the disk back to a laboratory and use a lot of sensitive (and expensive) equipment to look for the faint ``echoes'' of the original data underneath the overwritten data.  If the data has only been overwritten once, it's not even that hard.

The best way to remove something irretrievably is to destroy the media it's on with acid, melt it down, or the like.  For cheap removable media like floppy disks, this is the preferred method.  However, hard drives are expensive and hard to melt, so the shred utility tries to achieve a similar effect non-destructively.

This uses many overwrite passes, with the data patterns chosen to maximize the damage they do to the old data.  While this will work on floppies, the patterns are designed for best effect on hard drives. For more details, see the source code and Peter Gutmann's paper Secure Deletion of Data from Magnetic and Solid-State Memory, from the proceedings of the Sixth USENIX Security Symposium (San Jose, California, 22--25 July, 1996).  The paper is also available online http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html.

Please note that shred relies on a very important assumption: that the filesystem overwrites data in place.  This is the traditional way to do things, but many modern filesystem designs do not satisfy this assumption.  Exceptions include:

  * Log-structured or journaled filesystems, such as those supplied with AIX and Solaris.

  * Filesystems that write redundant data and carry on even if some writes fail, such as RAID-based filesystems.

  * Filesystems that make snapshots, such as Network Appliance's NFS server.

  * Filesystems that cache in temporary locations, such as NFS version 3 clients.

  * Compressed filesystems.

If you are not sure how your filesystem operates, then you should assume that it does not overwrite data in place, which means that shred cannot reliably operate on regular files in your filesystem.

Generally speaking, it is more reliable to shred a device than a file, since this bypasses the problem of filesystem design mentioned above. However, even shredding devices is not always completely reliable.  For example, most disks map out bad sectors invisibly to the application; if the bad sectors contain sensitive data, shred won't be able to destroy it.

shred makes no attempt to detect or report these problem, just as it makes no attempt to do anything about backups.  However, since it is more reliable to shred devices than files, shred by default does not truncate or remove the output file.  This default is more suitable for devices, which typically cannot be truncated and should not be removed.

     shred [OPTION]... FILE[...]

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

-f
--force
     Override file permissions if necessary to allow overwriting.

-NUMBER
-n NUMBER
--iterations=NUMBER
     By default, shred uses 25 passes of overwrite.  This is enough for all of the useful overwrite patterns to be used at least once. You can reduce this to save time, or increase it if you have a lot of time to waste.

-s BYTES
--size=BYTES
     Shred the first BYTES bytes of the file. The default is to shred the whole file.  BYTES can be followed by a size specification like k, M, or G to specify a multiple. See Block size.

-u
--remove
     After shredding a file, truncate it (if possible) and then remove it. If a file has multiple links, only the named links will be removed.

-v
--verbose
     Display status updates as sterilization proceeds.

-x
--exact
     Normally, shred rounds the file size up to the next multiple of the filesystem block size to fully erase the last block of the file. This option suppresses that behavior. Thus, by default if you shred a 10-byte file on a system with 512-byte blocks, the resulting file will be 512 bytes long.  With this option, shred does not increase the size of the file.

-z
--zero
     Normally, the last pass that shred writes is made up of random data.  If this would be conspicuous on your hard drive (for example, because it looks like encrypted data), or you just think it's tidier, the --zero option adds an additional overwrite pass with all zero bits.  This is in addition to the number of passes specified by the --iterations option.

-
     Shred standard output.

     This argument is considered an option.  If the common -- option has been used to indicate the end of options on the command line, then - will be interpreted as an ordinary file name.

     The intended use of this is to shred a removed temporary file. For example

          i=`tempfile -m 0600`
          exec 3<>"$i"
          rm -- "$i"
          echo "Hello, world" >&3
          shred - >&3
          exec 3>-

     Note that the shell command shred - >file does not shred the contents of FILE, since it truncates FILE before invoking shred.  Use the command shred file or (if using a Bourne-compatible shell) the command shred - 1<>file instead.

You might use the following command to erase all trace of the file system you'd created on the floppy disk in your first drive. That command takes about 20 minutes to erase a 1.44MB floppy.

     shred --verbose /dev/fd0

Similarly, to erase all data on a selected partition of your hard disk, you could give a command like this:

     shred --verbose /dev/sda5

Special file types
******************

This chapter describes commands which create special types of files (and rmdir, which removes directories, one special file type).

Although Unix-like operating systems have markedly fewer special file types than others, not everything can be treated only as the undifferentiated byte stream of normal files.  For example, when a file is created or removed, the system must record this information, which it does in a directory---a special type of file.  Although you can read directories as normal files, if you're curious, in order for the system to do its job it must impose a structure, a certain order, on the bytes of the file.  Thus it is a ``special'' type of file.

Besides directories, other special file types include named pipes (FIFOs), symbolic links, sockets, and so-called special files.

ln: Make links between files
============================

ln makes links between files.  By default, it makes hard links; with the -s option, it makes symbolic (or soft) links. Synopses:

     ln [OPTION]... TARGET [LINKNAME]
     ln [OPTION]... TARGET... DIRECTORY

  * If the last argument names an existing directory, ln creates a link to each TARGET file in that directory, using the TARGETs' names.  (But see the description of the --no-dereference option below.)

  * If two filenames are given, ln creates a link from the second to the first.

  * If one TARGET is given, ln creates a link to that file in the current directory.

  * It is an error if the last argument is not a directory and more than two files are given.  Without -f or -i (see below), ln will not remove an existing file.  Use the --backup option to make ln rename existing files.

A hard link is another name for an existing file; the link and the original are indistinguishable.  Technically speaking, they share the same inode, and the inode contains all the information about a file---indeed, it is not incorrect to say that the inode is the file.  On all existing implementations, you cannot make a hard link to a directory, and hard links cannot cross filesystem boundaries.  (These restrictions are not mandated by POSIX, however.)

Symbolic links (symlinks for short), on the other hand, are a special file type (which not all kernels support: System V release 3 (and older) systems lack symlinks) in which the link file actually refers to a different file, by name.  When most operations (opening, reading, writing, and so on) are passed the symbolic link file, the kernel automatically dereferences the link and operates on the target of the link.  But some operations (e.g., removing) work on the link file itself, rather than on its target.  See Symbolic Links (The GNU C Library Reference Manual).

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

-b
--backup[=METHOD]
     See Backup options. Make a backup of each file that would otherwise be overwritten or removed.

-d
-F
--directory
     Allow the super-user to make hard links to directories.

-f
--force
     Remove existing destination files.

-i
--interactive
     Prompt whether to remove existing destination files.

-n
--no-dereference
     When given an explicit destination that is a symlink to a directory, treat that destination as if it were a normal file.

     When the destination is an actual directory (not a symlink to one), there is no ambiguity.  The link is created in that directory. But when the specified destination is a symlink to a directory, there are two ways to treat the user's request.  ln can treat the destination just as it would a normal directory and create the link in it.  On the other hand, the destination can be viewed as a non-directory---as the symlink itself.  In that case, ln must delete or backup that symlink before creating the new link. The default is to treat a destination that is a symlink to a directory just like a directory.

-s
--symbolic
     Make symbolic links instead of hard links.  This option merely produces an error message on systems that do not support symbolic links.

-S SUFFIX
--suffix=SUFFIX
     Append SUFFIX to each backup file made with -b. See Backup options.

--target-directory=DIRECTORY
     Specify the destination DIRECTORY. See Target directory.

-v
--verbose
     Print the name of each file before linking it.

-V METHOD
--version-control=METHOD
     Change the type of backups made with -b.  The METHOD argument can be none (or off), numbered (or t), existing (or nil), or never (or simple).  See Backup options.

Examples:

     ln -s /some/name  # creates link ./name pointing to /some/name
     ln -s /some/name myname  # creates link ./myname pointing to /some/name
     ln -s a b ..      # creates links ../a and ../b pointing to ./a and ./b

mkdir: Make directories
=======================

mkdir creates directories with the specified names.  Synopsis:

     mkdir [OPTION]... NAME...

If a NAME is an existing file but not a directory, mkdir prints a warning message on stderr and will exit with a status of 1 after processing any remaining NAMEs.  The same is done when a NAME is an existing directory and the -p option is not given.  If a NAME is an existing directory and the -p option is given, mkdir will ignore it. That is, mkdir will not print a warning, raise an error, or change the mode of the directory (even if the -m option is given), and will move on to processing any remaining NAMEs.

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

-m MODE
--mode=MODE
     Set the mode of created directories to MODE, which is symbolic as in chmod and uses a=rwx (read, write and execute allowed for everyone) minus the bits set in the umask for the point of the departure.  See File permissions.

-p
--parents
     Make any missing parent directories for each argument.  The mode for parent directories is set to the umask modified by u+wx. Ignore arguments corresponding to existing directories.

-v

--verbose
     Print a message for each created directory.  This is most useful with --parents.

mkfifo: Make FIFOs (named pipes)
================================

mkfifo creates FIFOs (also called named pipes) with the specified names.  Synopsis:

     mkfifo [OPTION] NAME...

A FIFO is a special file type that permits independent processes to communicate.  One process opens the FIFO file for writing, and another for reading, after which data can flow as with the usual anonymous pipe in shells or elsewhere.

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

-m MODE
--mode=MODE
     Set the mode of created FIFOs to MODE, which is symbolic as in chmod and uses a=rw (read and write allowed for everyone) minus the bits set in the umask for the point of departure.  See File permissions.

mknod: Make block or character special files
============================================

mknod creates a FIFO, character special file, or block special file with the specified name.  Synopsis:

     mknod [OPTION]... NAME TYPE [MAJOR MINOR]

Unlike the phrase ``special file type'' above, the term special file has a technical meaning on Unix: something that can generate or receive data.  Usually this corresponds to a physical piece of hardware, e.g., a printer or a disk.  (These files are typically created at system-configuration time.)  The mknod command is what creates files of this type.  Such devices can be read either a character at a time or a ``block'' (many characters) at a time, hence we say there are block special files and character special files.

The arguments after NAME specify the type of file to make:

p
     for a FIFO

b
     for a block special file

c
     for a character special file

When making a block or character special file, the major and minor device numbers must be given after the file type.

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

-m MODE
--mode=MODE
     Set the mode of created files to MODE, which is symbolic as in chmod and uses a=rw minus the bits set in the umask as the point of departure.  See File permissions.

rmdir: Remove empty directories
===============================

rmdir removes empty directories.  Synopsis:

     rmdir [OPTION]... DIRECTORY...

If any DIRECTORY argument does not refer to an existing empty directory, it is an error.

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

--ignore-fail-on-non-empty
     Ignore each failure to remove a directory that is solely because the directory is non-empty.

-p
--parents
     Remove DIRECTORY, then try to remove each component of DIRECTORY. So, for example, rmdir -p a/b/c is similar to rmdir a/b/c a/b a. As such, it fails if any of those directories turns out not to be empty. Use the --ignore-fail-on-non-empty option to make it so such a failure does not evoke a diagnostic and does not cause rmdir to exit unsuccessfully.

-v

--verbose
     Give a diagnostic for each successful removal. DIRECTORY is removed.

See rm invocation, for how to remove non-empty directories (recursively).

Changing file attributes
************************

A file is not merely its contents, a name, and a file type (see Special file types).  A file also has an owner (a userid), a group (a group id), permissions (what the owner can do with the file, what people in the group can do, and what everyone else can do), various timestamps, and other information.  Collectively, we call these a file's attributes.

These commands change file attributes.

chown: Change file owner and group
==================================

chown changes the user and/or group ownership of each given FILE to NEW-OWNER or to the user and group of an existing reference file. Synopsis:

     chown [OPTION]... {NEW-OWNER | --reference=REF_FILE} FILE...

If used, NEW-OWNER specifies the new owner and/or group as follows (with no embedded white space):

     [OWNER] [ [:] [GROUP] ]

Specifically:

owner
     If only an OWNER (a user name or numeric user id) is given, that user is made the owner of each given file, and the files' group is not changed.

owner:group
     If the OWNER is followed by a colon and a GROUP (a group name or numeric group id), with no spaces between them, the group ownership of the files is changed as well (to GROUP).

owner:
     If a colon but no group name follows OWNER, that user is made the owner of the files and the group of the files is changed to OWNER's login group.

:group
     If the colon and following GROUP are given, but the owner is omitted, only the group of the files is changed; in this case, chown performs the same function as chgrp.

You may use . in place of the : separator.  This is a GNU extension for compatibility with older scripts. New scripts should avoid the use of . because GNU chown may fail if OWNER contains . characters.

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

-c
--changes
     Verbosely describe the action for each FILE whose ownership actually changes.

-f
--silent
--quiet
     Do not print error messages about files whose ownership cannot be changed.

--from=OLD-OWNER
     Change a FILE's ownership only if it has current attributes specified by OLD-OWNER.  OLD-OWNER has the same form as NEW-OWNER described above. This option is useful primarily from a security standpoint in that it narrows considerably the window of potential abuse. For example, to reflect a UID numbering change for one user's files without an option like this, root might run

          find / -owner OLDUSER -print0 | xargs -0 chown NEWUSER

     But that is dangerous because the interval between when the find tests the existing file's owner and when the chown is actually run may be quite large. One way to narrow the gap would be to invoke chown for each file as it is found:

          find / -owner OLDUSER -exec chown NEWUSER {} \;

     But that is very slow if there are many affected files. With this option, it is safer (the gap is narrower still) though still not perfect:

          chown -R --from=OLDUSER NEWUSER /

--dereference
     Do not act on symbolic links themselves but rather on what they point to.

-h
--no-dereference
     Act on symbolic links themselves instead of what they point to. This is the default. This mode relies on the lchown system call. On systems that do not provide the lchown system call, chown fails when a file specified on the command line is a symbolic link. By default, no diagnostic is issued for symbolic links encountered during a recursive traversal, but see --verbose.

--reference=REF_FILE
     Change the user and group of each FILE to be the same as those of REF_FILE.  If REF_FILE is a symbolic link, do not use the user and group of the symbolic link, but rather those of the file it refers to.

-v
--verbose
     Output a diagnostic for every file processed. If a symbolic link is encountered during a recursive traversal on a system without the lchown system call, and --no-dereference is in effect, then issue a diagnostic saying neither the symbolic link nor its referent is being changed.

-R
--recursive
     Recursively change ownership of directories and their contents.

chgrp: Change group ownership
=============================

chgrp changes the group ownership of each given FILE to GROUP (which can be either a group name or a numeric group id) or to the group of an existing reference file.  Synopsis:

     chgrp [OPTION]... {GROUP | --reference=REF_FILE} FILE...

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

-c
--changes
     Verbosely describe the action for each FILE whose group actually changes.

-f
--silent
--quiet
     Do not print error messages about files whose group cannot be changed.

--dereference
     Do not act on symbolic links themselves but rather on what they point to.

-h
--no-dereference
     Act on symbolic links themselves instead of what they point to. This is the default. This mode relies on the lchown system call. On systems that do not provide the lchown system call, chgrp fails when a file specified on the command line is a symbolic link. By default, no diagnostic is issued for symbolic links encountered during a recursive traversal, but see --verbose.

--reference=REF_FILE
     Change the group of each FILE to be the same as that of REF_FILE. If REF_FILE is a symbolic link, do not use the group of the symbolic link, but rather that of the file it refers to.

-v
--verbose
     Output a diagnostic for every file processed. If a symbolic link is encountered during a recursive traversal on a system without the lchown system call, and --no-dereference is in effect, then issue a diagnostic saying neither the symbolic link nor its referent is being changed.

-R
--recursive
     Recursively change the group ownership of directories and their contents.

chmod: Change access permissions
================================

chmod changes the access permissions of the named files.  Synopsis:

     chmod [OPTION]... {MODE | --reference=REF_FILE} FILE...

chmod never changes the permissions of symbolic links, since the chmod system call cannot change their permissions. This is not a problem since the permissions of symbolic links are never used.  However, for each symbolic link listed on the command line, chmod changes the permissions of the pointed-to file. In contrast, chmod ignores symbolic links encountered during recursive directory traversals.

If used, MODE specifies the new permissions. For details, see the section on File permissions.

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

-c
--changes
     Verbosely describe the action for each FILE whose permissions actually changes.

-f
--silent
--quiet
     Do not print error messages about files whose permissions cannot be changed.

-v
--verbose
     Verbosely describe the action or non-action taken for every FILE.

--reference=REF_FILE
     Change the mode of each FILE to be the same as that of REF_FILE. See File permissions. If REF_FILE is a symbolic link, do not use the mode of the symbolic link, but rather that of the file it refers to.

-R
--recursive
     Recursively change permissions of directories and their contents.

touch: Change file timestamps
=============================

touch changes the access and/or modification times of the specified files.  Synopsis:

     touch [OPTION]... FILE...

If the first FILE would be a valid argument to the -t option and no timestamp is given with any of the -d, -r, or -t options and the -- argument is not given, that argument is interpreted as the time for the other files instead of as a file name.  Warning: this usage is obsolescent, and future versions of POSIX will require that support for it be withdrawn.  Use -t instead.

Any FILE that does not exist is created empty.

If changing both the access and modification times to the current time, touch can change the timestamps for files that the user running it does not own but has write permission for.  Otherwise, the user must own the files.

Although touch provides options for changing two of the times -- the times of last access and modification -- of a file, there is actually a third one as well: the inode change time.  This is often referred to as a file's ctime. The inode change time represents the time when the file's meta-information last changed. One common example of this is when the permissions of a file change.  Changing the permissions doesn't access the file, so the atime doesn't change, nor does it modify the file, so the mtime doesn't change.  Yet, something about the file itself has changed, and this must be noted somewhere.  This is the job of the ctime field. This is necessary, so that, for example, a backup program can make a fresh copy of the file, including the new permissions value. Another operation that modifies a file's ctime without affecting the others is renaming.  In any case, it is not possible, in normal operations, for a user to change the ctime field to a user-specified value.

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

-a
--time=atime
--time=access
--time=use
     Change the access time only.

-c
--no-create
     Do not create files that do not exist.

-d
--date=time
     Use TIME instead of the current time.  It can contain month names, timezones, am and pm, etc.  See Date input formats.

-f
     Ignored; for compatibility with BSD versions of touch.

-m
--time=mtime
--time=modify
     Change the modification time only.

-r FILE
--reference=FILE
     Use the times of the reference FILE instead of the current time.

-t [[CC]YY]MMDDhhmm[.ss]
     Use the argument (optional four-digit or two-digit years, months, days, hours, minutes, optional seconds) instead of the current time. If the year is specified with only two digits, then CC is 20 for years in the range 0 ... 68, and 19 for years in 69 ... 99.  If no digits of the year are specified, the argument is interpreted as a date in the current year.

Disk usage
**********

No disk can hold an infinite amount of data.  These commands report on how much disk storage is in use or available.  (This has nothing much to do with how much main memory, i.e., RAM, a program is using when it runs; for that, you want ps or pstat or swap or some such command.)

df: Report filesystem disk space usage
======================================

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

     df [OPTION]... [FILE]...

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

Normally the disk space is printed in units of 1024 bytes, but this can be overridden (see Block size).

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

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

-a
--all
     Include in the listing filesystems that have a size of 0 blocks, which are omitted by default.  Such filesystems are typically special-purpose pseudo-filesystems, such as automounter entries.  Also, filesystems of type ``ignore'' or ``auto'', supported by some operating systems, are only included if this option is specified.

-h
--human-readable
     Append a size letter such as M for megabytes to each size. Powers of 1024 are used, not 1000; M stands for 1,048,576 bytes. Use the -H or --si option if you prefer powers of 1000.

-H
--si
     Append a size letter such as M for megabytes to each size.  (SI is the International System of Units, which defines these letters as prefixes.)  Powers of 1000 are used, not 1024; M stands for 1,000,000 bytes.  Use the -h or --human-readable option if you prefer powers of 1024.

-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
--kilobytes
     Print sizes in 1024-byte blocks, overriding the default block size (see Block size).

-l
--local
     Limit the listing to local filesystems.  By default, remote filesystems are also listed.

-m
--megabytes
     Print sizes in megabyte (that is, 1,048,576-byte) blocks.

--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.

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

      1. The information about each filesystem 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. Non-integer values are rounded up, instead of being rounded down or rounded to the nearest integer.

      3. The labels in the header output line are changed to conform to POSIX.

--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 filesystems.

-t FSTYPE
--type=FSTYPE
     Limit the listing to filesystems of type FSTYPE.  Multiple filesystem types can be specified by giving multiple -t options. By default, nothing is omitted.

-T
--print-type
     Print each filesystem'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 filesystem, 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 filesystem on a locally-mounted hard disk.  (The system might even support more than one type here; Linux does.)

     hsfs, cdfs
          A filesystem on a CD-ROM drive.  HP-UX uses cdfs, most other systems use hsfs (hs for ``High Sierra'').

     pcfs
          An MS-DOS filesystem, usually on a diskette.

-x FSTYPE
--exclude-type=FSTYPE
     Limit the listing to filesystems not of type FSTYPE. Multiple filesystem types can be eliminated by giving multiple -x options.  By default, no filesystem types are omitted.

-v
     Ignored; for compatibility with System V versions of df.

du: Estimate file space usage
=============================

du reports the amount of disk space used by the specified files and for each subdirectory (of directory arguments).  Synopsis:

     du [OPTION]... [FILE]...

With no arguments, du reports the disk space for the current directory.  Normally the disk space is printed in units of 1024 bytes, but this can be overridden (see Block size).

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

-a
--all
     Show counts for all files, not just directories.

-b
--bytes
     Print sizes in bytes, overriding the default block size (see Block size).

-c
--total
     Print a grand total of all arguments after all arguments have been processed.  This can be used to find out the total disk usage of a given set of files or directories.

-D
--dereference-args
     Dereference symbolic links that are command line arguments. Does not affect other symbolic links.  This is helpful for finding out the disk usage of directories, such as /usr/tmp, which are often symbolic links.

-h
--human-readable
     Append a size letter such as M for megabytes to each size. Powers of 1024 are used, not 1000; M stands for 1,048,576 bytes. Use the -H or --si option if you prefer powers of 1000.

-H
--si
     Append a size letter such as M for megabytes to each size.  (SI is the International System of Units, which defines these letters as prefixes.)  Powers of 1000 are used, not 1024; M stands for 1,000,000 bytes.  Use the -h or --human-readable option if you prefer powers of 1024.

-k
--kilobytes
     Print sizes in 1024-byte blocks, overriding the default block size (see Block size).

-l
--count-links
     Count the size of all files, even if they have appeared already (as a hard link).

-L
--dereference
     Dereference symbolic links (show the disk space used by the file or directory that the link points to instead of the space used by the link).

--max-depth=DEPTH
     Show the total for each directory (and file if --all) that is at most MAX_DEPTH levels down from the root of the hierarchy.  The root is at level 0, so du --max-depth=0 is equivalent to du -s.

-m
--megabytes
     Print sizes in megabyte (that is, 1,048,576-byte) blocks.

-s
--summarize
     Display only a total for each argument.

-S
--separate-dirs
     Report the size of each directory separately, not including the sizes of subdirectories.

-x
--one-file-system
     Skip directories that are on different filesystems from the one that the argument being processed is on.

--exclude=PAT
     When recursing, skip subdirectories or files matching PAT. For example, du --exclude='*.o' excludes files whose names end in .o.

-X FILE
--exclude-from=FILE
     Like --exclude, except take the patterns to exclude from FILE, one per line.  If FILE is -, take the patterns from standard input.

On BSD systems, du reports sizes that are half the correct values for files that are NFS-mounted from HP-UX systems.  On HP-UX systems, it reports sizes that are twice the correct values for files that are NFS-mounted from BSD systems.  This is due to a flaw in HP-UX; it also affects the HP-UX du program.

sync: Synchronize data on disk with memory
==========================================

sync writes any data buffered in memory out to disk.  This can include (but is not limited to) modified superblocks, modified inodes, and delayed reads and writes.  This must be implemented by the kernel; The sync program does nothing but exercise the sync system call.

The kernel keeps data in memory to avoid doing (relatively slow) disk reads and writes.  This improves performance, but if the computer crashes, data may be lost or the filesystem corrupted as a result. sync ensures everything in memory is written to disk.

Any arguments are ignored, except for a lone --help or --version (see Common options).