This manual documents version 4.1 of the GNU file utilities.
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.
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.
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
--version
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]
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
numbered
t
existing
nil
simple
never
never is not to be
confused with none.
-S suffix
--suffix=suffix
-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
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
df command.
Similarly, DU_BLOCK_SIZE specifies the default for du and
LS_BLOCK_SIZE for ls.
BLOCK_SIZE
POSIXLY_CORRECT
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
human-readable,
or 10^3 = 1000 for si.
M
G
T
P
E
Z
Y
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.
Some GNU programs (at least cp, install, ln, and
mv) allow you to specify the target directory via this option:
--target-directory=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
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.
Each file has a set of permissions that control the kinds of access that users have to that file. The permissions for a file are also called its access mode. They can be represented either in symbolic form or as an octal number.
There are three kinds of permissions that a user can have for a file:
There are three categories of users who may have different permissions to perform any of the above operations on a file:
Files are given an owner and group when they are created. Usually the
owner is the current user and the group is the group of the directory
the file is in, but this varies with the operating system, the
filesystem the file is created on, and the way the file is created. You
can change the owner and group of a file by using the chown and
chgrp commands.
In addition to the three sets of three permissions listed above, a file's permissions have three special components, which affect only executable files (programs) and, on some systems, directories:
Symbolic modes represent changes to files' permissions as
operations on single-character symbols. They allow you to modify either
all or selected parts of files' permissions, optionally based on
their previous values, and perhaps on the current umask as well
(see Umask and Protection).
The format of symbolic modes is:
[ugoa...][[+-=][rwxXstugo...]...][,...]
The following sections describe the operators and other details of symbolic modes.
The basic symbolic operations on a file's permissions are adding, removing, and setting the permission that certain users have to read, write, and execute the file. These operations have the following format:
users operation permissions
The spaces between the three parts above are shown for readability only; symbolic modes cannot contain spaces.
The users part tells which users' access to the file is changed. It consists of one or more of the following letters (or it can be empty; see Umask and Protection, for a description of what happens then). When more than one of these letters is given, the order that they are in does not matter.
u
g
o
a
ugo.
The operation part tells how to change the affected users' access to the file, and is one of the following symbols:
+
-
=
The permissions part tells what kind of access to the file should
be changed; it is zero or more of the following letters. As with the
users part, the order does not matter when more than one letter is
given. Omitting the permissions part is useful only with the
= operation, where it gives the specified users no access
at all to the file.
r
w
x
For example, to give everyone permission to read and write a file, but not to execute it, use:
a=rw
To remove write permission for from all users other than the file's owner, use:
go-w
The above command does not affect the access that the owner of the file has to it, nor does it affect whether other users can read or execute the file.
To give everyone except a file's owner no permission to do anything with that file, use the mode below. Other users could still remove the file, if they have write permission on the directory it is in.
go=
Another way to specify the same thing is:
og-rxw
You can base a file's permissions on its existing permissions. To do
this, instead of using r, w, or x after the
operator, you use the letter u, g, or o. For
example, the mode
o+g
adds the permissions for users who are in a file's group to the
permissions that other users have for the file. Thus, if the file
started out as mode 664 (rw-rw-r--), the above mode would change
it to mode 666 (rw-rw-rw-). If the file had started out as mode
741 (rwxr----x), the above mode would change it to mode 745
(rwxr--r-x). The - and = operations work
analogously.
In addition to changing a file's read, write, and execute permissions, you can change its special permissions. See Mode Structure, for a summary of these permissions.
To change a file's permission to set the user ID on execution, use
u in the users part of the symbolic mode and
s in the permissions part.
To change a file's permission to set the group ID on execution, use
g in the users part of the symbolic mode and
s in the permissions part.
To change a file's permission to stay permanently on the swap device,
use o in the users part of the symbolic mode and
t in the permissions part.
For example, to add set user ID permission to a program, you can use the mode:
u+s
To remove both set user ID and set group ID permission from it, you can use the mode:
ug-s
To cause a program to be saved on the swap device, you can use the mode:
o+t
Remember that the special permissions only affect files that are
executable, plus, on some systems, directories (on which they have
different meanings; see Mode Structure).
Also, the combinations u+t, g+t, and o+s have no effect.
The = operator is not very useful with special permissions; for
example, the mode:
o=t
does cause the file to be saved on the swap device, but it also removes all read, write, and execute permissions that users not in the file's group might have had for it.
There is one more special type of symbolic permission: if you use
X instead of x, execute permission is affected only if the
file already had execute permission or is a directory. It affects
directories' execute permission even if they did not initially have any
execute permissions set.
For example, this mode:
a+X
gives all users permission to execute files (or search directories) if anyone could before.
The format of symbolic modes is actually more complex than described above (see Setting Permissions). It provides two ways to make multiple changes to files' permissions.
The first way is to specify multiple operation and permissions parts after a users part in the symbolic mode.
For example, the mode:
og+rX-w
gives users other than the owner of the file read permission and, if it is a directory or if someone already had execute permission to it, gives them execute permission; and it also denies them write permission to the file. It does not affect the permission that the owner of the file has for it. The above mode is equivalent to the two modes:
og+rX og-w
The second way to make multiple changes is to specify more than one simple symbolic mode, separated by commas. For example, the mode:
a+r,go-w
gives everyone permission to read the file and removes write permission on it for all users except its owner. Another example:
u=rwx,g=rx,o=
sets all of the non-special permissions for the file explicitly. (It gives users who are not in the file's group no permission at all for it.)
The two methods can be combined. The mode:
a+r,g+x-w
gives all users permission to read the file, and gives users who are in the file's group permission to execute it, as well, but not permission to write to it. The above mode could be written in several different ways; another is:
u+r,g+rx,o+r,g-w
If the users part of a symbolic mode is omitted, it defaults to
a (affect all users), except that any permissions that are
set in the system variable umask are not affected.
The value of umask can be set using the
umask command. Its default value varies from system to system.
Omitting the users part of a symbolic mode is generally not useful
with operations other than +. It is useful with + because
it allows you to use umask as an easily customizable protection
against giving away more permission to files than you intended to.
As an example, if umask has the value 2, which removes write
permission for users who are not in the file's group, then the mode:
+w
adds permission to write to the file to its owner and to other users who are in the file's group, but not to other users. In contrast, the mode:
a+w
ignores umask, and does give write permission for
the file to all users.
File permissions are stored internally as integers. As an alternative to giving a symbolic mode, you can give an octal (base 8) number that corresponds to the internal representation of the new mode. This number is always interpreted in octal; you do not have to add a leading 0, as you do in C. Mode 0055 is the same as mode 55.
A numeric mode is usually shorter than the corresponding symbolic mode, but it is limited in that it cannot take into account a file's previous permissions; it can only set them absolutely.
On most systems, the permissions granted to the user, to other users in the file's group, and to other users not in the file's group are each stored as three bits, which are represented as one octal digit. The three special permissions are also each stored as one bit, and they are as a group represented as another octal digit. Here is how the bits are arranged, starting with the lowest valued bit:
Value in Corresponding
Mode Permission
Other users not in the file's group:
1 Execute
2 Write
4 Read
Other users in the file's group:
10 Execute
20 Write
40 Read
The file's owner:
100 Execute
200 Write
400 Read
Special permissions:
1000 Save text image on swap device
2000 Set group ID on execution
4000 Set user ID on execution
For example, numeric mode 4755 corresponds to symbolic mode
u=rwxs,go=rx, and numeric mode 664 corresponds to symbolic mode
ug=rw,o=r. Numeric mode 0 corresponds to symbolic mode
ugo=.
First, a quote:
Our units of temporal measurement, from seconds on up to months, are so complicated, asymmetrical and disjunctive so as to make coherent mental reckoning in time all but impossible. Indeed, had some tyrannical god contrived to enslave our minds to time, to make it all but impossible for us to escape subjection to sodden routines and unpleasant surprises, he could hardly have done better than handing down our present system. It is like a set of trapezoidal building blocks, with no vertical or horizontal surfaces, like a language in which the simplest thought demands ornate constructions, useless particles and lengthy circumlocutions. Unlike the more successful patterns of language and science, which enable us to face experience boldly or at least level-headedly, our system of temporal calculation silently and persistently encourages our terror of time. ... It is as though architects had to measure length in feet, width in meters and height in ells; as though basic instruction manuals demanded a knowledge of five different languages. It is no wonder then that we often look into our own immediate past or future, last Tuesday or a week from Sunday, with feelings of helpless confusion. ...-- Robert Grudin, Time and the Art of Living.
This section describes the textual date representations that GNU
programs accept. These are the strings you, as a user, can supply as
arguments to the various programs. The C interface (via the
getdate function) is not described here.
Although the date syntax here can represent any possible time since the
year zero, computer integers often cannot represent such a wide range of
time. On POSIX systems, the clock starts at 1970-01-01 00:00:00
UTC: POSIX does not require support for times before the
POSIX Epoch and times far in the future. Traditional Unix systems
have 32-bit signed time_t and can represent times from 1901-12-13
20:45:52 through 2038-01-19 03:14:07 UTC. Systems with 64-bit
signed time_t can represent all the times in the known
lifetime of the universe.
A date is a string, possibly empty, containing many items separated by whitespace. The whitespace may be omitted when no ambiguity arises. The empty string means the beginning of today (i.e., midnight). Order of the items is immaterial. A date string may contain many flavors of items:
We describe each of these item types in turn, below.
A few numbers may be written out in words in most contexts. This is
most useful for specifying day of the week items or relative items (see
below). Here is the list: first for 1, next for 2,
third for 3, fourth for 4, fifth for 5,
sixth for 6, seventh for 7, eighth for 8,
ninth for 9, tenth for 10, eleventh for 11 and
twelfth for 12. Also, last means exactly -1.
When a month is written this way, it is still considered to be written numerically, instead of being "spelled in full"; this changes the allowed strings.
In the current implementation, only English is supported for words and
abbreviations like AM, DST, EST, first,
January, Sunday, tomorrow, and year.
The output of date is not always acceptable as a date string,
not only because of the language problem, but also because there is no
standard meaning for time zone items like IST. When using
date to generate a date string intended to be parsed later,
specify a date format that is independent of language and that does not
use time zone items other than UTC and Z. Here are some
ways to do this:
$ LC_ALL=C TZ=UTC0 date Fri Dec 15 19:48:05 UTC 2000 $ TZ=UTC0 date +"%Y-%m-%d %H:%M:%SZ" 2000-12-15 19:48:05Z $ date --iso-8601=seconds # a GNU extension 2000-12-15T11:48:05-0800 $ date --rfc-822 # a GNU extension Fri, 15 Dec 2000 11:48:05 -0800 $ date +"%Y-%m-%d %H:%M:%S %z" # %z is a GNU extension. 2000-12-15 11:48:05 -0800
Alphabetic case is completely ignored in dates. Comments may be introduced between round parentheses, as long as included parentheses are properly nested. Hyphens not followed by a digit are currently ignored. Leading zeros on numbers are ignored.
A calendar date item specifies a day of the year. It is specified differently, depending on whether the month is specified numerically or literally. All these strings specify the same calendar date:
1972-09-24 # ISO 8601.
72-9-24 # Assume 19xx for 69 through 99,
# 20xx for 00 through 68.
72-09-24 # Leading zeros are ignored.
9/24/72 # Common U.S. writing.
24 September 1972
24 Sept 72 # September has a special abbreviation.
24 Sep 72 # Three-letter abbreviations always allowed.
Sep 24, 1972
24-sep-72
24sep72
The year can also be omitted. In this case, the last specified year is used, or the current year if none. For example:
9/24 sep 24
Here are the rules.
For numeric months, the ISO 8601 format
year-month-day is allowed, where year is
any positive number, month is a number between 01 and 12, and
day is a number between 01 and 31. A leading zero must be present
if a number is less than ten. If year is 68 or smaller, then 2000
is added to it; otherwise, if year is less than 100,
then 1900 is added to it. The construct
month/day/year, popular in the United States,
is accepted. Also month/day, omitting the year.
Literal months may be spelled out in full: January,
February, March, April, May, June,
July, August, September, October,
November or December. Literal months may be abbreviated
to their first three letters, possibly followed by an abbreviating dot.
It is also permitted to write Sept instead of September.
When months are written literally, the calendar date may be given as any of the following:
day month year day month month day year day-month-year
Or, omitting the year:
month day
A time of day item in date strings specifies the time on a given day. Here are some examples, all of which represent the same time:
20:02:0 20:02 8:02pm 20:02-0500 # In EST (U.S. Eastern Standard Time).
More generally, the time of the day may be given as
hour:minute:second, where hour is
a number between 0 and 23, minute is a number between 0 and
59, and second is a number between 0 and 59. Alternatively,
:second can be omitted, in which case it is taken to
be zero.
If the time is followed by am or pm (or a.m.
or p.m.), hour is restricted to run from 1 to 12, and
:minute may be omitted (taken to be zero). am
indicates the first half of the day, pm indicates the second
half of the day. In this notation, 12 is the predecessor of 1:
midnight is 12am while noon is 12pm.
(This is the zero-oriented interpretation of 12am and 12pm,
as opposed to the old tradition derived from Latin
which uses 12m for noon and 12pm for midnight.)
The time may alternatively be followed by a time zone correction,
expressed as shhmm, where s is +
or -, hh is a number of zone hours and mm is a number
of zone minutes. When a time zone correction is given this way, it
forces interpretation of the time relative to
Coordinated Universal Time (UTC), overriding any previous
specification for the time zone or the local time zone. The minute
part of the time of the day may not be elided when a time zone correction
is used. This is the best way to specify a time zone correction by
fractional parts of an hour.
Either am/pm or a time zone correction may be specified,
but not both.
A time zone item specifies an international time zone, indicated
by a small set of letters, e.g., UTC or Z
for Coordinated Universal
Time. Any included periods are ignored. By following a
non-daylight-saving time zone by the string DST in a separate
word (that is, separated by some white space), the corresponding
daylight saving time zone may be specified.
Time zone items other than UTC and Z
are obsolescent and are not recommended, because they
are ambiguous; for example, EST has a different meaning in
Australia than in the United States. Instead, it's better to use
unambiguous numeric time zone corrections like -0500, as
described in the previous section.
The explicit mention of a day of the week will forward the date (only if necessary) to reach that day of the week in the future.
Days of the week may be spelled out in full: Sunday,
Monday, Tuesday, Wednesday, Thursday,
Friday or Saturday. Days may be abbreviated to their
first three letters, optionally followed by a period. The special
abbreviations Tues for Tuesday, Wednes for
Wednesday and Thur or Thurs for Thursday are
also allowed.
A number may precede a day of the week item to move forward
supplementary weeks. It is best used in expression like third
monday. In this context, last day or next
day is also acceptable; they move one week before or after
the day that day by itself would represent.
A comma following a day of the week item is ignored.
Relative items adjust a date (or the current date if none) forward or backward. The effects of relative items accumulate. Here are some examples:
1 year 1 year ago 3 years 2 days
The unit of time displacement may be selected by the string year
or month for moving by whole years or months. These are fuzzy
units, as years and months are not all of equal duration. More precise
units are fortnight which is worth 14 days, week worth 7
days, day worth 24 hours, hour worth 60 minutes,
minute or min worth 60 seconds, and second or
sec worth one second. An s suffix on these units is
accepted and ignored.
The unit of time may be preceded by a multiplier, given as an optionally
signed number. Unsigned numbers are taken as positively signed. No
number at all implies 1 for a multiplier. Following a relative item by
the string ago is equivalent to preceding the unit by a
multiplier with value -1.
The string tomorrow is worth one day in the future (equivalent
to day), the string yesterday is worth
one day in the past (equivalent to day ago).
The strings now or today are relative items corresponding
to zero-valued time displacement, these strings come from the fact
a zero-valued time displacement represents the current time when not
otherwise changed by previous items. They may be used to stress other
items, like in 12:00 today. The string this also has
the meaning of a zero-valued time displacement, but is preferred in
date strings like this thursday.
When a relative item causes the resulting date to cross a boundary where the clocks were adjusted, typically for daylight-saving time, the resulting date and time are adjusted accordingly.
The precise interpretation of a pure decimal number depends on the context in the date string.
If the decimal number is of the form yyyymmdd and no other calendar date item (see Calendar date items) appears before it in the date string, then yyyy is read as the year, mm as the month number and dd as the day of the month, for the specified calendar date.
If the decimal number is of the form hhmm and no other time of day item appears before it in the date string, then hh is read as the hour of the day and mm as the minute of the hour, for the specified time of the day. mm can also be omitted.
If both a calendar date and a time of day appear to the left of a number in the date string, but no relative item, then the number overrides the year.
getdategetdate was originally implemented by Steven M. Bellovin
(smb@research.att.com) while at the University of North Carolina
at Chapel Hill. The code was later tweaked by a couple of people on
Usenet, then completely overhauled by Rich $alz (rsalz@bbn.com)
and Jim Berets (jberets@bbn.com) in August, 1990. Various
revisions for the GNU system were made by David MacKenzie, Jim Meyering,
Paul Eggert and others.
This chapter was originally produced by François Pinard
(pinard@iro.umontreal.ca) from the getdate.y source code,
and then edited by K. Berry (kb@cs.umb.edu).
This chapter describes the ls command and its variants dir
and vdir, which list information about files.
ls: List directory contentsThe 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.
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
..
-A
--almost-all
. and ...
-B
--ignore-backups
~, unless they are given on the
command line.
-d
--directory
-I PATTERN
--ignore=PATTERN
. 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
-R
--recursive
These options affect the information that ls displays. By
default, only file names are shown.
-D
--dired
-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=wordwhere word is the quoting style (see Formatting the file names).
-G
--no-group
ls, so we
provide this option for compatibility.)
-h
--human-readable
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
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
-l
--format=long
--format=verbose
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
S
t
T
x
-
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
--format=long with --no-group .
This option is provided for compatibility with other versions of ls.
-s
--size
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.
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
-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
-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
-S
--sort=size
-t
--sort=time
mtime in the inode), newest first.
-u
--time=atime
--time=access
--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
-f does.) This is especially useful when listing very large
directories, since not doing any sorting can be noticeably faster.
-v
--sort=version
-X
--sort=extension
.); files with no extension are sorted first.
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
These options affect the appearance of the overall output.
-1
--format=single-column
ls when standard
output is not a terminal.
-C
--format=vertical
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]
--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
*. The file type
indicators are / for directories, @ for symbolic links,
| for FIFOs, = for sockets, and nothing for regular files.
--full-time
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.
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
none
file-type
/ 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
* for executable regular files, otherwise behave as for
file-type. This is the same as the -F or
--classify option.
-k
--kilobytes
-m
--format=commas
, (a comma and a space).
-n
--numeric-uid-gid
-p
--file-type
--indicator-style=file-type
-F, except that executables are not marked.
-x format
--format=across
--format=horizontal
-T cols
--tabsize=cols
ls uses tabs where possible in the output, for efficiency. If
cols is zero, do not use tabs at all.
-w
--width=cols
COLUMNS is used if it is set; otherwise the default
is 80.
These options change how file names themselves are printed.
-b
--escape
--quoting-style=escape
-N
--literal
-q
--hide-control-chars
ls.
-Q
--quote-name
--quoting-style=c
--quoting-style=word
literal
shell
shell-always
c
-Q or --quote-name option.
escape
c except omit the surrounding double-quote
characters; this is the same as the -b or --escape option.
clocale
c except use quotation marks appropriate for the
locale.
locale
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
ls.
dir: Briefly list directory contentsdir (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 contentsvdir (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 lsdircolors 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
SHELL
environment variable is set and does not end with csh or
tcsh.
-c
--csh
--c-shell
SHELL ends with
csh or tcsh.
-p
--print-database
This chapter describes the commands for basic file manipulation: copying, moving (renaming), and deleting (removing).
cp: Copy files and directoriescp 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
ls -U may list the entries in a copied
directory in a different order).
Equivalent to -dpR.
-b
--backup[=method]
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
-f
--force
--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
-i
--interactive
-l
--link
-L
--dereference
-p
--preserve
-P
--parents
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
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
-r just above).
--remove-destination
-f above).
--sparse=when
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
always
efs filesystems in SGI IRIX 5.3 and
earlier), but the output file is on another type of filesystem.
never
mkswap command,
since such a file must not have any holes.
--strip-trailing-slashes
-s
--symbolic-link
/) 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
-b.
See Backup options.
--target-directory=directory
-v
--verbose
-V method
--version-control=method
-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
dd: Convert and copy a filedd 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
of=file
conv=notrunc is given, dd truncates file to zero
bytes (or the size specified with seek=).
ibs=bytes
obs=bytes
bs=bytes
ibs and obs.
cbs=bytes
skip=blocks
ibs-byte blocks in the input file before copying.
seek=blocks
obs-byte blocks in the output file before copying.
count=blocks
ibs-byte blocks from the input file, instead
of everything until the end of the file.
conv=conversion[,conversion]...
Conversions:
ascii
ebcdic
ibm
block
cbs bytes, replacing the
input newline with a space and padding with spaces as necessary.
unblock
cbs-sized input block with a
newline.
lcase
ucase
swab
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
notrunc
sync
ibs with trailing zero bytes.
When use with block or unblock, pad with spaces instead of
zero bytes.
install: Copy files and set attributesinstall 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]
-c
install.
-d
--directory
install, which
gives directories that it creates the default attributes.)
-g group
--group=group
-m mode
--mode=mode
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
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
-s
--strip
-S suffix
--suffix=suffix
-b.
See Backup options.
--target-directory=directory
-v
--verbose
-V method
--version-control=method
-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) filesmv 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]
-f
--force
-i
--interactive
y or
Y, the file is skipped.
-u
--update
-v
--verbose
--strip-trailing-slashes
-S suffix
--suffix=suffix
-b.
See Backup options.
--target-directory=directory
-V method
--version-control=method
-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 directoriesrm 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
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
--interactive (-i) option.
-i
--interactive
y or Y, the file is skipped.
Ignore any previous --force (-f) option.
-r
-R
--recursive
-v
--verbose
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 securelyshred 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:
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
-NUMBER
-n NUMBER
--iterations=NUMBER
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
k, M, or G to specify a multiple. See Block size.
-u
--remove
-v
--verbose
-x
--exact
-z
--zero
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.
-
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
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 filesln 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
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.)
ln creates a link from the
second to the first.
ln creates a link to that
file in the current directory.
-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 program accepts the following options. Also see Common options.
-b
--backup[=method]
-d
-F
--directory
-f
--force
-i
--interactive
-n
--no-dereference
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
-S suffix
--suffix=suffix
-b.
See Backup options.
--target-directory=directory
-v
--verbose
-V method
--version-control=method
-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 directoriesmkdir 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
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
u+wx.
Ignore arguments corresponding to existing directories.
-v
--verbose
--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
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 filesmknod 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
b
c
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
chmod and uses a=rw minus the bits set in the umask as the point
of departure. See File permissions.
rmdir: Remove empty directoriesrmdir 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
-p
--parents
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
See rm invocation, for how to remove non-empty directories (recursively).
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 groupchown 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:
:group
:
:group
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
-f
--silent
--quiet
--from=old-owner
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
-h
--no-dereference
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
-v
--verbose
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
chgrp: Change group ownershipchgrp 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
-f
--silent
--quiet
--dereference
-h
--no-dereference
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
-v
--verbose
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
chmod: Change access permissionschmod 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
-f
--silent
--quiet
-v
--verbose
--reference=ref_file
-R
--recursive
touch: Change file timestampstouch 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
-c
--no-create
-d
--date=time
am and pm, etc. See Date input formats.
-f
touch.
-m
--time=mtime
--time=modify
-r file
--reference=file
-t [[CC]YY]MMDDhhmm[.ss]
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 usagedf 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
-h
--human-readable
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
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
-k
--kilobytes
-l
--local
-m
--megabytes
--no-sync
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
--sync
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
-t options.
By default, nothing is omitted.
-T
--print-type
-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
4.2, ufs, efs...
hsfs, cdfs
cdfs, most other
systems use hsfs (hs for "High Sierra").
pcfs
-x fstype
--exclude-type=fstype
-x options. By default, no filesystem types are omitted.
-v
df.
du: Estimate file space usagedu 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
-b
--bytes
-c
--total
-D
--dereference-args
/usr/tmp, which
are often symbolic links.
-h
--human-readable
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
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
-l
--count-links
-L
--dereference
--max-depth=DEPTH
du --max-depth=0 is equivalent to du -s.
-m
--megabytes
-s
--summarize
-S
--separate-dirs
-x
--one-file-system
--exclude=PAT
du --exclude='*.o' excludes files whose names
end in .o.
-X FILE
--exclude-from=FILE
--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 memorysync 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).
-: shred invocation
- and Unix rm-, removing files beginning with: rm invocation
--all: du invocation, df invocation, Which files are listed
--almost-all: Which files are listed
--archive: cp invocation
--backup: ln invocation, mv invocation, install invocation, cp invocation, Backup options
--block-size=size: Block size
--bourne-shell: dircolors invocation
--bytes: du invocation
--c-shell: dircolors invocation
--changes: chmod invocation, chgrp invocation, chown invocation
--classify: General output formatting
--color: General output formatting
--count-links: du invocation
--csh: dircolors invocation
--date: touch invocation
--dereference: du invocation, chgrp invocation, chown invocation, cp invocation, Which files are listed
--dereference-args: du invocation
--directory: ln invocation, rm invocation, install invocation, Which files are listed
--dired: What information is listed
--escape: Formatting the file names
--exact: shred invocation
--exclude-from=FILE: du invocation
--exclude-type: df invocation
--exclude=PAT: du invocation
--file-type: General output formatting
--force: ln invocation, shred invocation, rm invocation, mv invocation, cp invocation
--format: General output formatting, What information is listed
--from: chown invocation
--full-time: General output formatting
--group: install invocation
--help: Common options
--hide-control-chars: Formatting the file names
--human-readable: du invocation, df invocation, What information is listed, Block size
--ignore-backups: Which files are listed
--ignore-fail-on-non-empty: rmdir invocation
--ignore=pattern: Which files are listed
--indicator-style: General output formatting
--inode: What information is listed
--inodes: df invocation
--interactive: ln invocation, rm invocation, mv invocation, cp invocation
--iterations=NUMBER: shred invocation
--kilobytes: du invocation, df invocation, General output formatting, Block size
--link: cp invocation
--literal: Formatting the file names
--local: df invocation
--max-depth=DEPTH: du invocation
--megabytes: du invocation, df invocation
--mode: mknod invocation, mkfifo invocation, mkdir invocation, install invocation
--no-create: touch invocation
--no-dereference: chgrp invocation, chown invocation, ln invocation, cp invocation
--no-group: What information is listed
--no-sync: df invocation
--numeric-uid-gid: General output formatting
--one-file-system: du invocation, cp invocation
--owner: install invocation
--parents: rmdir invocation, mkdir invocation, cp invocation
--portability: df invocation
--preserve: cp invocation
--preserve-timestamps: install invocation
--print-database: dircolors invocation
--print-type: df invocation
--quiet: chmod invocation, chgrp invocation, chown invocation
--quote-name: Formatting the file names
--quoting-style: Formatting the file names
--recursive: chmod invocation, chgrp invocation, chown invocation, rm invocation, cp invocation, Which files are listed
--reference: touch invocation, chmod invocation, chgrp invocation, chown invocation
--remove: shred invocation
--remove-destination: cp invocation
--reverse: Sorting the output
--separate-dirs: du invocation
--sh: dircolors invocation
--show-control-chars: Formatting the file names
--si: du invocation, df invocation, What information is listed, Block size
--silent: chmod invocation, chgrp invocation, chown invocation
--size: What information is listed
--size=BYTES: shred invocation
--sort: Sorting the output
--sparse=when: cp invocation
--strip: install invocation
--strip-trailing-slashes: mv invocation, cp invocation
--suffix: ln invocation, mv invocation, install invocation, cp invocation, Backup options
--summarize: du invocation
--symbolic: ln invocation
--symbolic-link: cp invocation
--sync: df invocation
--tabsize: General output formatting
--target-directory: ln invocation, mv invocation, install invocation, cp invocation, Target directory
--time: touch invocation, Sorting the output
--total: du invocation
--type: df invocation
--update: mv invocation
--verbose: chmod invocation, chgrp invocation, chown invocation, rmdir invocation, mkdir invocation, ln invocation, shred invocation, rm invocation, mv invocation, install invocation, cp invocation
--version: Common options
--version-control: ln invocation, mv invocation, install invocation, cp invocation, Backup options
--width: General output formatting
--zero: shred invocation
-1: General output formatting
-a: du invocation, df invocation, touch invocation, cp invocation
-A: Which files are listed
-a: Which files are listed
-b: du invocation, ln invocation, mv invocation, install invocation, cp invocation, dircolors invocation, Formatting the file names
-B: Which files are listed
-b: Backup options
-c: du invocation, touch invocation, chmod invocation, chgrp invocation, chown invocation, install invocation, dircolors invocation
-C: General output formatting
-c: Sorting the output
-D: du invocation
-d: touch invocation, ln invocation, rm invocation, install invocation, cp invocation
-D: What information is listed
-d: Which files are listed
-f: touch invocation, chmod invocation, chgrp invocation, chown invocation, ln invocation
-F: ln invocation
-f: shred invocation, rm invocation, mv invocation, cp invocation
-F: General output formatting
-f: Sorting the output
-g: install invocation
-G: What information is listed
-g (ignored)-H: du invocation
-h: du invocation
-H: df invocation
-h: df invocation, chgrp invocation, chown invocation
-H: cp invocation, What information is listed
-h: What information is listed, Block size
-i: df invocation, ln invocation, rm invocation, mv invocation, cp invocation, What information is listed
-I: Which files are listed
-k: du invocation, df invocation, General output formatting, Block size
-L: du invocation
-l: du invocation, df invocation
-L: cp invocation
-l: cp invocation, What information is listed
-L: Which files are listed
-m: du invocation, df invocation, touch invocation, mknod invocation, mkfifo invocation, mkdir invocation, install invocation, General output formatting
-n: ln invocation
-N: Formatting the file names
-n: General output formatting
-n NUMBER: shred invocation
-o: install invocation, What information is listed
-P: df invocation
-p: rmdir invocation, mkdir invocation, install invocation
-P: cp invocation
-p: cp invocation, dircolors invocation
-Q: Formatting the file names
-q: Formatting the file names
-r: touch invocation
-R: chmod invocation, chgrp invocation, chown invocation, rm invocation
-r: rm invocation
-R: cp invocation
-r: Sorting the output
-R: Which files are listed
-S: du invocation
-s: du invocation
-S: ln invocation
-s: ln invocation
-S: mv invocation, install invocation
-s: install invocation
-S: cp invocation
-s: cp invocation
-S: Sorting the output
-s: What information is listed
-S: Backup options
-s BYTES: shred invocation
-T: df invocation
-t: df invocation
-T: General output formatting
-t: Sorting the output
-u: shred invocation, mv invocation
-U: Sorting the output
-u: Sorting the output
-v: chmod invocation, chgrp invocation, chown invocation, rmdir invocation, mkdir invocation
-V: ln invocation
-v: ln invocation, shred invocation, rm invocation
-V: mv invocation
-v: mv invocation
-V: install invocation
-v: install invocation
-V: cp invocation
-v: cp invocation, Sorting the output
-w: General output formatting
-x: du invocation, df invocation, shred invocation, cp invocation, General output formatting
-X: Sorting the output
-X FILE: du invocation
-z: shred invocation
4.2 filesystem typeaccess time, changingaccess time, printing or sorting files byacross, listing filesago in date stringsalternate ebcdic, converting toalways color optionam in date stringsascii, converting toatime, changingatime, printing or sorting files bygetdate: Authors of getdate
auto color optionb for block special fileblock (space-padding)BLOCK_SIZE: Block size
bs: dd invocation
touch compatibility: touch invocation
c for character special filecbs: dd invocation
cdfs filesystem typechgrp: chgrp invocation
chmod: chmod invocation
chown: chown invocation
COLUMNS: General output formatting
commas, outputting between filesconv: dd invocation
count: dd invocation
cp: cp invocation
csh syntax for color setup: dircolors invocation
ctime, printing or sorting byday in date stringsdd: dd invocation
df: df invocation
DF_BLOCK_SIZE: Block size
dir: dir invocation
dircolors: dircolors invocation
unlink: rm invocation
du: du invocation
DU_BLOCK_SIZE: Block size
ebcdic, converting toefs filesystem typedu: du invocation
existing backup methodextension, sorting files by-, removing: rm invocation
first in date stringsfortnight in date stringsfsck: rm invocation
getdate: Date input formats
du: du invocation
horizontal, listing fileshour in date stringshsfs filesystem typeibs: dd invocation
if: dd invocation
install: install invocation
last day: Day of week items
last in date stringslcase, converting tolchown: chgrp invocation, chown invocation
du: du invocation
ln: ln invocation
long ls formatls: ls invocation
LS_BLOCK_SIZE: Block size
LS_COLORS: dircolors invocation
midnight in date stringsminute in date stringsmkdir: mkdir invocation
mkfifo: mkfifo invocation
mknod: mknod invocation
modification time, sorting files bymodify time, changingmonth in date stringsmtime, changingmv: mv invocation
next day: Day of week items
next in date stringsnoerror: dd invocation
none backup methodnone color optionnone, sorting option for lsnoon in date stringsnotrunc: dd invocation
now in date stringsnumbered backup methodobs: dd invocation
of: dd invocation
du to: du invocation
p for FIFO filecp: cp invocation
pcfs: df invocation
ls: What information is listed
pm in date stringsPOSIXLY_CORRECT, and block sizeln: ln invocation
mv: mv invocation
rm: rm invocation
read system call, and holesrm: rm invocation
rmdir: rmdir invocation
root as default ownerseek: dd invocation
sh syntax for color setup: dircolors invocation
SHELL environment variable, and colorshred: shred invocation
simple backup methodSIMPLE_BACKUP_SUFFIX: Backup options
single-column output of filessize of files, sorting files byskip: dd invocation
ls output: Sorting the output
status time, printing or sorting byswab (byte-swapping)du: du invocation
sync: sync invocation
sync (padding with nulls)this in date stringstime: touch invocation
today in date stringstomorrow in date stringstouch: touch invocation
ucase, converting toufs filesystem typeunblock: dd invocation
unlink: rm invocation
use time, changinguse time, printing or sorting files byvdir: vdir invocation
verbose ls formatversion, sorting option for lsversion-control Emacs variableVERSION_CONTROL: ln invocation, mv invocation, install invocation, cp invocation, Backup options
vertical sorted files in columnsweek in date stringsyear in date stringsyesterday in date strings