     [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.
     * 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.
     * 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 (C) 1994 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies.

Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation.

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

This manual minimally 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-gnu-utils@prep.ai.mit.edu.  Remember to include the version number, machine architecture, input files, and any other information needed to reproduce the bug.  See Bugs (GNU CC).

This manual is based on the Unix man pages in the distribution, which were originally written by David MacKenzie and updated by Jim Meyering. Franc,ois 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 these programs.  Rather than writing identical descriptions for each of the programs, they are described here.  (In fact, every GNU program accepts (or should accept) these options.)

--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, mv, and ln) 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
     Make backups of files that are about to be overwritten or removed. Without this option, the original versions are destroyed.

-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.

-V METHOD
--version-control=METHOD
     Use METHOD to determine the type of backups made with -b. If this option is not specified, the value of the VERSION_CONTROL environment variable is used.  And if VERSION_CONTROL is not set, the default backup type is existing.

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

     t
     numbered
          Always make numbered backups.

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

     never
     simple
          Always make simple backups.

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

     [file perm.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 filename.  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); otherwise, they are listed one per line.

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.

Also, 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
--ignore
     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 filename does not match a wildcard at the start of PATTERN.

-L
--dereference
     List the files linked to by symbolic links instead of listing the contents of the links.

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

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

These options affect the information that ls displays.  By default, only filenames 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 which record the byte position of the beginning and end of each filename 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// BEG1 END1 ...

-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.)

-i
--inode
     Print the inode number (also called the file serial number and index number) of each file to the left of the filename.  (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 6 months old or more than 1 hour into the future, the timestamp contains the year instead of the time of day.

     For each directory that is listed, preface the files with a line total BLOCKS, where BLOCKS is the total disk space used by all files in that directory.  By default, 1024-byte blocks are used; if the environment variable POSIXLY_CORRECT is set, 512-byte blocks are used (unless the -k option is given). The BLOCKS computed counts each hard link separately; this is arguably a bug.

     This output format is the default for the GNU v and vdir programs.

-s
--size
     Print the size of each file in 1024-byte blocks to the left of the filename.  If the environment variable POSIXLY_CORRECT is set, 512-byte blocks are used instead, unless the -k option is given (see General output formatting).

     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
     Sort according to the status change time (the ctime in the inode).  If the long listing format (-l) is being used, print the status change time instead of the modification 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 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
--time=use
     Sort by access time (the atime in the inode).  If the long listing format is being used, print the last 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.

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

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.

-F
--classify
     Append a character to each filename 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 the same as date's default; it's not possible to change this, 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.

-k
--kilobytes
     If file sizes are being listed, print them in kilobytes.  This overrides the environment variable POSIXLY_CORRECT.

-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
     Append a character to each filename indicating the file type. This is like -F, except that executables are not marked.

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

-T
--tabsize=COLS
     Assume that each tabstop is COLS columns wide.  The default is 8. ls uses tabs where possible in the output, for efficiency.

-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 filenames
------------------------

These options change how filenames themselves are printed.

-b
--escape
     Quote nongraphic characters in filenames using alphabetic and octal backslash sequences like those used in C.

-N
--literal
     Do not quote filenames.

-q
--hide-control-chars
     Print question marks instead of nongraphic characters in filenames. This is the default.

-Q
--quote-name
     Enclose filenames in double quotes and quote nongraphic characters as in C.

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

The dir program (also installed as d) is equivalent to ls -C; that is, files are by default always listed in columns, sorted vertically.

See ls.

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

The vdir program (also installed v)is equivalent to ls -l; that is, files are by default listed in long format.

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.

If the source file contains holes, cp copies them and other blocks of zero bytes as holes.  Otherwise, files are written just as they are read.  (A hole is a sequence of zero bytes that does not occupy any physical disk blocks; the read system call reads these as zeroes.)

By default, cp does not copy directories.  It also refuses to copy a file onto itself.

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.  Equivalent to -dpR.

-b
--backup
     Make backups of files that are about to be overwritten or removed. See Backup options.

-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
     Remove existing destination files.

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

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

-p
--preserve
     Preserve the original files' owner, group, permissions, and timestamps.

-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.

-r
     Copy directories recursively, copying any non-directories and non-symbolic links (that is, FIFOs and special files) as if they were regular files.  This means trying to read the data in each source file and writing it to the destination.  Thus, with this option, cp may well hang indefinitely reading a FIFO, unless something else happens to be writing it.

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

-s
--symbolic-link
     Make symbolic links instead of copies of non-directories.  All source filenames 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.

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

-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 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.

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

dd copies a file (from standard input to standard output, by default) with a changeable I/O blocksize, 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, k=1024, w=2, xM=M.

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 obs-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.

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.

-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's 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 0755---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.

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

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 only regular files across filesystems.

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.

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

-b
--backup
     Make backups of files that are about to be overwritten or removed. See Backup options.

-f
--force
     Remove existing destination files and never prompt the user.

-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.

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

-V METHOD
--version-control=METHOD
     Change the type of backups made with -b.  The METHOD argument can be 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
     Remove directories with unlink instead of rmdir, and don't require a directory to be empty before trying to unlink it.  Only works if you have appropriate privileges.  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.

-i
--interactive
     Prompt whether to remove each file.  If the response does not begin with y or Y, the file is skipped.

-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 being 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.

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]... SOURCE [DEST]
     ln [OPTION]... SOURCE... DIRECTORY

If the last argument names an existing directory, ln links each SOURCE file into a file with the same name in that directory. (But see the description of the --no-dereference option below.) If only one file is given, it links that file into the current directory. Otherwise, if only two files are given, it links the first onto the second.  It is an error if the last argument is not a directory and more than two files are given.  By default, it does not remove 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 links to directories, 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; in particular, 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 (GNU C library).

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

-b
--backup
     Make backups of files that are about to be overwritten or removed. See Backup options.

-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 used with --force and an explicit destination that is a symlink to a directory, remove (or move it with --backup) that symlink before making any link.

     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.

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

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

-V METHOD
--version-control=METHOD
     Change the type of backups made with -b.  The METHOD argument can be numbered (or t), existing (or nil), or never (or simple).  See Backup options.

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

mkdir creates directories with the specified names.  Synopsis:

     mkdir [OPTION]... NAME...

It is not an error if a NAME is already a directory; mkdir simply proceeds.  But if a NAME is an existing file and is anything but a directory, mkdir complains.

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 0777 (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.

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 0666 (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 (buffered) special file

c
     for a character (buffered) special file

u
     for a character (unbuffered) 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 0666 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.

-p
--parents
     Remove any parent directories that become empty after an argument DIRECTORY is removed.

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

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

Files are not merely contents, a name, and a file type (see Special file types).  They also have 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 all this 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.  Synopsis:

     chown [OPTION]... NEW-OWNER FILE...

The first non-option argument, 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
owner:group
     If the OWNER is followed by a colon or dot 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.
owner:
     If a colon or dot 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
:group
     If the colon or dot 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.

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.

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

-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. Synopsis:

     chgrp [OPTION]... GROUP 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.

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

-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 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.

The first non-option argument, MODE, specifies the new permissions.  See the section below for details.

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.

-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 filename.

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.

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 invocation (Shell utilities).

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

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

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

-t MMDDhhmm[[CC]YY][.ss]
     Use the argument (months, days, hours, minutes, optional century and years, optional seconds) instead of the current time.

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.

Disk space is shown in 1024-byte blocks by default, unless the environment variable POSIXLY_CORRECT is set, in which case 512-byte blocks are used (unless the -k option is given).

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

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

-k
--kilobytes
     Print sizes in 1024-byte blocks.  This overrides the environment variable POSIXLY_CORRECT.

--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 the results may be slightly out of date.

-P
--portability
     Use the POSIX output format.  This is like the default format except that 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.

--sync
     Invoke the sync system call before getting any usage data. On some systems, 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.  The output is in 1024-byte units by default, unless the environment variable POSIXLY_CORRECT is set, in which case 512-byte blocks are used (unless -k is specified).

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, instead of kilobytes.

-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.

-k
--kilobytes
     Print sizes in kilobytes.  This overrides the environment variable POSIXLY_CORRECT.

-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).

-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.

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).