phpMan

/* Void Main's man pages */

{ phpMan } else { main(); }

CHMOD(1P) POSIX Programmer's Manual CHMOD(1P)

PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (con-
sult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on
Linux.

NAME
chmod - change the file modes

SYNOPSIS
chmod [-R] mode file ...

DESCRIPTION
The chmod utility shall change any or all of the file mode bits of the file named by each file operand in the way speci-
fied by the mode operand.

It is implementation-defined whether and how the chmod utility affects any alternate or additional file access control
mechanism (see the Base Definitions volume of IEEE Std 1003.1-2001, Section 4.4, File Access Permissions) being used for
the specified file.

Only a process whose effective user ID matches the user ID of the file, or a process with the appropriate privileges,
shall be permitted to change the file mode bits of a file.

OPTIONS
The chmod utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax
Guidelines.

The following option shall be supported:

-R Recursively change file mode bits. For each file operand that names a directory, chmod shall change the file mode
bits of the directory and all files in the file hierarchy below it.

OPERANDS
The following operands shall be supported:

mode Represents the change to be made to the file mode bits of each file named by one of the file operands; see the
EXTENDED DESCRIPTION section.

file A pathname of a file whose file mode bits shall be modified.

STDIN
Not used.

INPUT FILES
None.

ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of chmod:

LANG Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions
volume of IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables for the precedence of international-
ization variables used to determine the values of locale categories.)

LC_ALL If set to a non-empty string value, override the values of all the other internationalization variables.

LC_CTYPE
Determine the locale for the interpretation of sequences of bytes of text data as characters (for example, single-
byte as opposed to multi-byte characters in arguments).

LC_MESSAGES
Determine the locale that should be used to affect the format and contents of diagnostic messages written to stan-
dard error.

NLSPATH
Determine the location of message catalogs for the processing of LC_MESSAGES .

ASYNCHRONOUS EVENTS
Default.

STDOUT
Not used.

STDERR
The standard error shall be used only for diagnostic messages.

OUTPUT FILES
None.

EXTENDED DESCRIPTION
The mode operand shall be either a symbolic_mode expression or a non-negative octal integer. The symbolic_mode form is
described by the grammar later in this section.

Each clause shall specify an operation to be performed on the current file mode bits of each file. The operations shall
be performed on each file in the order in which the clauses are specified.

The who symbols u, g, and o shall specify the user, group, and other parts of the file mode bits, respectively. A who
consisting of the symbol a shall be equivalent to ugo.

The perm symbols r, w, and x represent the read, write, and execute/ search portions of file mode bits, respectively. The
perm symbol s shall represent the set-user-ID-on-execution (when who contains or implies u) and set-group-ID-on-execution
(when who contains or implies g) bits.

The perm symbol X shall represent the execute/search portion of the file mode bits if the file is a directory or if the
current (unmodified) file mode bits have at least one of the execute bits (S_IXUSR, S_IXGRP, or S_IXOTH) set. It shall be
ignored if the file is not a directory and none of the execute bits are set in the current file mode bits.

The permcopy symbols u, g, and o shall represent the current permissions associated with the user, group, and other parts
of the file mode bits, respectively. For the remainder of this section, perm refers to the non-terminals perm and perm-
copy in the grammar.

If multiple actionlists are grouped with a single wholist in the grammar, each actionlist shall be applied in the order
specified with that wholist. The op symbols shall represent the operation performed, as follows:

+ If perm is not specified, the '+' operation shall not change the file mode bits.

If who is not specified, the file mode bits represented by perm for the owner, group, and other permissions, except for
those with corresponding bits in the file mode creation mask of the invoking process, shall be set.

Otherwise, the file mode bits represented by the specified who and perm values shall be set.

- If perm is not specified, the '-' operation shall not change the file mode bits.

Otherwise, the file mode bits represented by the specified who and perm values shall be cleared.

= Clear the file mode bits specified by the who value, or, if no who value is specified, all of the file mode bits
specified in this volume of IEEE Std 1003.1-2001.

If perm is not specified, the '=' operation shall make no further modifications to the file mode bits.

Otherwise, the file mode bits represented by the specified who and perm values shall be set.

When using the symbolic mode form on a regular file, it is implementation-defined whether or not:

* Requests to set the set-user-ID-on-execution or set-group-ID-on-execution bit when all execute bits are currently
clear and none are being set are ignored.

* Requests to clear all execute bits also clear the set-user-ID-on-execution and set-group-ID-on-execution bits.

* Requests to clear the set-user-ID-on-execution or set-group-ID-on-execution bits when all execute bits are currently
clear are ignored. However, if the command ls -l file writes an s in the position indicating that the set-user-ID-on-
execution or set-group-ID-on-execution is set, the commands chmod u-s file or chmod g-s file, respectively, shall not
be ignored.

When using the symbolic mode form on other file types, it is implementation-defined whether or not requests to set or
clear the set-user-ID-on-execution or set-group-ID-on-execution bits are honored.

If the who symbol o is used in conjunction with the perm symbol s with no other who symbols being specified, the set-
user-ID-on-execution and set-group-ID-on-execution bits shall not be modified. It shall not be an error to specify the
who symbol o in conjunction with the perm symbol s.

The perm symbol t shall specify the S_ISVTX bit. When used with a file of type directory, it can be used with the who
symbol a, or with no who symbol. It shall not be an error to specify a who symbol of u, g, or o in conjunction with the
perm symbol t, but the meaning of these combinations is unspecified. The effect when using the perm symbol t with any
file type other than directory is unspecified.

For an octal integer mode operand, the file mode bits shall be set absolutely.

For each bit set in the octal number, the corresponding file permission bit shown in the following table shall be set;
all other file permission bits shall be cleared. For regular files, for each bit set in the octal number corresponding to
the set-user-ID-on-execution or the set-group-ID-on-execution, bits shown in the following table shall be set; if these
bits are not set in the octal number, they are cleared. For other file types, it is implementation-defined whether or not
requests to set or clear the set-user-ID-on-execution or set-group-ID-on-execution bits are honored.

Octal Mode Bit Octal Mode Bit Octal Mode Bit Octal Mode Bit
4000 S_ISUID 0400 S_IRUSR 0040 S_IRGRP 0004 S_IROTH
2000 S_ISGID 0200 S_IWUSR 0020 S_IWGRP 0002 S_IWOTH
1000 S_ISVTX 0100 S_IXUSR 0010 S_IXGRP 0001 S_IXOTH

When bits are set in the octal number other than those listed in the table above, the behavior is unspecified.

Grammar for chmod
The grammar and lexical conventions in this section describe the syntax for the symbolic_mode operand. The general con-
ventions for this style of grammar are described in Grammar Conventions . A valid symbolic_mode can be represented as the
non-terminal symbol symbolic_mode in the grammar. This formal syntax shall take precedence over the preceding text syntax
description.

The lexical processing is based entirely on single characters. Implementations need not allow <blank>s within the single
argument being processed.

%start symbolic_mode
%%

symbolic_mode : clause
| symbolic_mode ',' clause
;

clause : actionlist
| wholist actionlist
;

wholist : who
| wholist who
;

who : 'u' | 'g' | 'o' | 'a'
;

actionlist : action
| actionlist action
;

action : op
| op permlist
| op permcopy
;

permcopy : 'u' | 'g' | 'o'
;

op : '+' | '-' | '='
;

permlist : perm
| perm permlist
;

perm : 'r' | 'w' | 'x' | 'X' | 's' | 't'
;

EXIT STATUS
The following exit values shall be returned:

0 The utility executed successfully and all requested changes were made.

>0 An error occurred.

CONSEQUENCES OF ERRORS
Default.

The following sections are informative.

APPLICATION USAGE
Some implementations of the chmod utility change the mode of a directory before the files in the directory when perform-
ing a recursive ( -R option) change; others change the directory mode after the files in the directory. If an application
tries to remove read or search permission for a file hierarchy, the removal attempt fails if the directory is changed
first; on the other hand, trying to re-enable permissions to a restricted hierarchy fails if directories are changed
last. Users should not try to make a hierarchy inaccessible to themselves.

Some implementations of chmod never used the process' umask when changing modes; systems conformant with this volume of
IEEE Std 1003.1-2001 do so when who is not specified. Note the difference between:

chmod a-w file

which removes all write permissions, and:

chmod -- -w file

which removes write permissions that would be allowed if file was created with the same umask.

Conforming applications should never assume that they know how the set-user-ID and set-group-ID bits on directories are
interpreted.

EXAMPLES
Mode Results
a+= Equivalent to a+, a=; clears all file
mode bits.
go+-w Equivalent to go+, go- w; clears group
and other write bits.
g=o-w Equivalent to g= o, g- w; sets group bit
to match other bits and then clears
group write bit.
g-r+w Equivalent to g- r, g+ w; clears group
read bit and sets group write bit.
uo=g Sets owner bits to match group bits and
sets other bits to match group bits.

RATIONALE
The functionality of chmod is described substantially through references to concepts defined in the System Interfaces
volume of IEEE Std 1003.1-2001. In this way, there is less duplication of effort required for describing the interactions
of permissions. However, the behavior of this utility is not described in terms of the chmod() function from the System
Interfaces volume of IEEE Std 1003.1-2001 because that specification requires certain side effects upon alternate file
access control mechanisms that might not be appropriate, depending on the implementation.

Implementations that support mandatory file and record locking as specified by the 1984 /usr/group standard historically
used the combination of set-group-ID bit set and group execute bit clear to indicate mandatory locking. This condition is
usually set or cleared with the symbolic mode perm symbol l instead of the perm symbols s and x so that the mandatory
locking mode is not changed without explicit indication that that was what the user intended. Therefore, the details on
how the implementation treats these conditions must be defined in the documentation. This volume of IEEE Std 1003.1-2001
does not require mandatory locking (nor does the System Interfaces volume of IEEE Std 1003.1-2001), but does allow it as
an extension. However, this volume of IEEE Std 1003.1-2001 does require that the ls and chmod utilities work consistently
in this area. If ls -l file indicates that the set-group-ID bit is set, chmod g-s file must clear it (assuming appropri-
ate privileges exist to change modes).

The System V and BSD versions use different exit status codes. Some implementations used the exit status as a count of
the number of errors that occurred; this practice is unworkable since it can overflow the range of valid exit status val-
ues. This problem is avoided here by specifying only 0 and >0 as exit values.

The System Interfaces volume of IEEE Std 1003.1-2001 indicates that implementation-defined restrictions may cause the
S_ISUID and S_ISGID bits to be ignored. This volume of IEEE Std 1003.1-2001 allows the chmod utility to choose to modify
these bits before calling chmod() (or some function providing equivalent capabilities) for non-regular files. Among other
things, this allows implementations that use the set-user-ID and set-group-ID bits on directories to enable extended fea-
tures to handle these extensions in an intelligent manner.

The X perm symbol was adopted from BSD-based systems because it provides commonly desired functionality when doing recur-
sive ( -R option) modifications. Similar functionality is not provided by the find utility. Historical BSD versions of
chmod, however, only supported X with op+; it has been extended in this volume of IEEE Std 1003.1-2001 because it is also
useful with op=. (It has also been added for op- even though it duplicates x, in this case, because it is intuitive and
easier to explain.)

The grammar was extended with the permcopy non-terminal to allow historical-practice forms of symbolic modes like o= u -g
(that is, set the "other" permissions to the permissions of "owner" minus the permissions of "group").

FUTURE DIRECTIONS
None.

SEE ALSO
ls, umask, the System Interfaces volume of IEEE Std 1003.1-2001, chmod()

COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for
Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copy-
right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any
discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group
Standard is the referee document. The original Standard can be obtained online at http://www.open-
group.org/unix/online.html .

IEEE/The Open Group 2003 CHMOD(1P)