chmod.1

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)chmod.1	8.1	9/11/90
.TH chmod 1
.SH Name
chmod \- change file mode
.SH Syntax
.B chmod
[
.B \-fR
] 
.I mode file...
.SH Description
.NX R "chmod command"
.NX A "chmod command" "install command"
.NX R "mode" "changing"
Permissions on files are set according to 
.I mode
and
.I file
parameters.
.PP
For
.IR file ,
you can specify either a full or partial path.  You can specify
multiple files, separated by spaces.
.PP
For
.IR mode ,
you specify one of two variants: absolute mode or symbolic mode.
.SS Absolute Mode
For
.I mode
in absolute form, you specify an octal number constructed from the sum
of one or more of the following values:
.RS
.TP 10
4000
set user ID on execution (applies to executable files only)
.br
.ns
.TP 10
2000
set group ID on execution (applies to executable files only)
.br
.ns
.TP 10
1000
set sticky bit (see
.MS chmod 2
for more information)
.br
.ns
.TP 10
0400
read by owner
.br
.ns
.TP 10
0200
write by owner
.br
.ns
.TP 10
0100
execute, or search if 
.I file 
is a directory, by owner
.br
.ns
.TP 10
0040
read by group
.br
.ns
.TP 10
0020
write by group
.br
.ns
.TP 10
0010
execute, or search if 
.I file 
is a directory, by group
.br
.ns
.TP 10
0004
read by others
.br
.ns
.TP 10
0002
write by others
.br
.ns
.TP 10
0001 
execute, or search if
.I file
is a directory, by others
.RE
.PP
For example, the absolute mode value that provides read, write, and 
execute permission to owner, read and execute permission to group, and
read and execute permission to others is 755 (400+200+100+40+10+4+1).
The absolute mode value that provides read, write, and execute
permission to owner and no permission to group or others is 700
(400+200+100).
.SS Symbolic Mode
To specify
.I mode
in symbolic form, use the following format:
.IP
.RI [ who ]
.I op permission
.RI [ "op permission" "] ..."
.NT
Spaces are included in the preceding format so that you can read the
arguments; however, as will be shown in examples that follow, you do
not enter spaces between mode arguments.
.NE
.PP
Specify
.I who
using the letters
.B u
(for owner),
.B g
(for group) and
.B o
(for others) either alone or in combination.  You can also specify the
letter
.B a
(for all), which is is equivalent to the letter combination
.B ugo.
If you omit the
.I who
parameter,
.B a
is assumed.  For more information, see 
.MS umask 2 .
.PP
For the
.I op
parameter, specify the plus sign
.RB ( + )
to add 
.I permission
to the file's mode, the minus sign
.RB ( \- )
to remove
.I permission
from the 
file's mode, or the equal sign
.RB ( = )
to assign
.I permission
absolutely (denying or revoking any permission not explicitly specified
following the equal sign).  The first command in the following example
provides group with execute permission for 
.PN filea
in addition to any other permissions group currently has for
.PN filea .
The second command limits the permission that group has for
.PN fileb
to execute alone:
.EX
chmod g+x filea
chmod g=x fileb
.EE
.PP
For the
.I permission
parameter, specify any combination of the letters
.B r
(read),
.B w
(write),
.B x
(execute),
.B s
(set owner or group id), and
.B t
(save text \- sticky).  Alternatively, you can specify the letter
.BR u ,
.BR g ,
or
.B o
to set
.I permission
for the
.I who
parameter to be the same as the permission currently granted to the
user category indicated by the letter.  In the following example, the
group
.RB ( g )
is given the same permissions on 
.PN filea
as currently granted to owner
.RB ( u ):
.EX
chmod g=u filea
.EE
.PP
You can revoke all permissions by specifying the
.I who
argument followed by
.BR = ,
and omitting the
.I permission
argument.  For example, the following command removes all permissions
from others for 
.PN fileb:
.EX
chmod o= fileb
.EE
.PP
When specifying more than one symbolic mode for
.IR file ,
separate the modes with commas. The mode changes are applied in the
sequence specified.  In the following example, write permission is
added to the permissions already granted to the owner of 
.PN filea
and group is then granted the same permissions on 
.PN filea
as granted the owner:
.EX
chmod u+w,g=u filea
.EE
.SH Options
.IP \-f 5
Inhibits display of errors that are returned if
.PN chmod
fails to change the mode on a file.
.IP \-R
Causes 
.PN chmod 
to recursively descend any directories subordinate to
.I file
and to set the specified mode for each file encountered.  However,
when symbolic links are encountered, 
.PN chmod
does not change the mode of the link file and does not traverse
the path associated with the link.  Note that the 
.PN \-R 
option is useful only when
.I file
identifies a directory that is not empty.
.SH Restrictions
.NX R "chmod command" "restricted"
The 
.I permission
letter
.B s
is used only with 
.I who 
letter
.B u
or
.B g.
.PP
Only the owner of a file  or someone logged on as superuser may change
the mode of that file.
.SH Examples
Using absolute mode, provide read, write, and search permission to
the owner, and read and search permission to others for a directory
named 
.PN public:
.EX
chmod 755 ~harris/public
.EE
.NX R(e) "chmod command"
.PP
Using absolute mode, set the UID for 
.PN progrmb 
execution to be the UID of
of the file owner rather than the UID of the user
running the program as follows:
.EX
chmod 4000 progrmb
.EE
.PP
Using symbolic mode, perform the same operation as described for 
the preceding example:
.EX
chmod u=s progrmb
.EE
.PP
Using symbolic mode, deny write permission to others for the file
.PN ourspec:
.EX
chmod o\-w ourspec
.EE
.PP
Using symbolic mode, give execute permission on file 
.PN myprog
to all user 
categories:
.EX
chmod +x myprog
.EE
.PP
Using symbolic mode, give write permission to all group members,
deny write permission to others, and give search permission to owner
on 
.PN docdir:
.EX
chmod g+w,o\-r,u+x docdir
.EE
.PP
Using symbolic mode, give read and execute permissions to others for a 
directory named 
.PN programs ,
and then recursively descend the paths subordinate to 
.PN programs, 
adding the  same permissions for others on all files and directories
included in the subordinate paths:
.EX
chmod \-R o+rx programs
.EE
.NT
In the preceding example, if 
.PN programs
were the name of a file rather than a directory, 
.PN chmod
would change the mode only of the 
.PN programs 
file.
.NE
.SH See Also
ls(1), chmod(2), stat(2), umask(2), chown(8)