chmod.2

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 2 代码 · 共 148 行

.\" SCCSID: @(#)chmod.2	2.6	8/18/87
.TH chmod 2
.SH Name
chmod, fchmod \- change mode of file
.SH Syntax
.nf
#include <sys/types.h>
#include <sys/stat.h>
.PP
chmod(\fIpath, mode\fP)
char *\fIpath\fP;
mode_t\ \fImode\fP;
.PP
fchmod(\fIfd, mode\fP)
int fd;
mode_t\ \fImode\fP;
.fi
.SH Description
.NXR "chmod system call"
.NXR "fchmod system call"
.NXR "file" "changing mode"
.NXR "file" "setting protection"
The file whose name
is provided by \fIpath\fP
or referenced by the descriptor
.I fd
has its mode changed to
.IR mode .
Modes are constructed by
ORing
combinations of the following:
.IP "S_ISUID" 12
\- 04000  set user ID on execution
.IP "S_ISGID"
\- 02000  set group ID on execution
.IP "S_ISVTX"
\- 01000  save text image after execution
.IP "S_IRUSR"
\- 00400  read by owner
.IP "S_IWUSR"
\- 00200  write by owner
.IP "S_IXUSR"
\- 00100  execute (search on directory) by owner
.IP "S_IRWXG"
\- 00070  read, write, execute (search) by group
.IP "S_IRWXO"
\- 00007  read, write, execute (search) by others
.PP
If an executable file is set up for sharing (the default),
the mode S_ISVTX prevents the system from
abandoning the swap-space image of the program-text portion
of the file when its last user
terminates.
The ability to set this bit is restricted to the superuser.
.PP
If the mode S_ISVTX (sticky bit) is set on a directory, an unprivileged
user cannot delete or the rename files of other users in that directory.
For more information on the sticky bit, see 
.MS sticky 8 .
.PP
Only the owner of a file or the superuser can change the mode.
.PP
Writing a file or changing the owner of a file
clears the set-user-id and set-group-id bits of that file. Turning off
these bits when a file is written or its owner changed protects the
file from
remaining set-user-id or set-group-id after being modified. If a file,
specifically a program, 
remained set-user-id or set-group-id after being modified, that file
could allow unauthorized access to other files or accounts. 
.SH Environment
.SS System Five
ELOOP is a possible error condition.
.SH Return Values
Upon successful completion, a value of 0 is returned.
Otherwise, a value of \-1 is returned, and
.PN errno
is set to indicate the error.
.SH Diagnostics
The
.PN chmod
system call fails and the file mode remains unchanged under the
following conditions:
.TP 15
[EACCES]
Search permission is denied on a component of the path prefix.
.TP 15
[EFAULT]
The
.I path
argument points outside the process's allocated address space.
.TP 15
[EIO]
An I/O error occurred while reading from or writing to
the file system.
.TP 15
[ELOOP]
Too many symbolic links were encountered in translating the pathname.
.TP 15
[ENAMETOOLONG]
A pathname component exceeds 255 characters, or
an entire pathname exceeds 1023 characters.
.TP 15
[ENOENT]
The named file does not exist.
.TP 15
[ENOTDIR]
A component of the path prefix is not a directory.
.TP 15
[EPERM]
The effective user ID does not match the owner of the file and
the effective user ID is not the superuser.
.TP 15
[EROFS]
The named file resides on a read-only file system.
.TP 15
[ESTALE]
The file handle given in the argument is invalid.  Either the file referred
to by that file handle no longer exists or it has been revoked.
.PP  
The 
.PN fchmod
system call
fails under the following conditions: 
.TP 15
[EBADF]
The descriptor is not valid.
.TP 15
[EINVAL]
The
.I fd
refers to a socket, not to a file.
.TP 15
[EIO]
An I/O error occurred while reading from or writing to
the file system.
.TP 15
[EROFS]
The file resides on a read-only file system.
.TP 15
[ETIMEDOUT]
A connect request or remote file operation failed
because the connected party
did not respond after a period
of time determined by the communications protocol.
.SH See Also
open(2), chown(2)