chmod.2

Unix操作系统minix 2.0源码

.\" Copyright (c) 1980 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)chmod.2	6.5 (Berkeley) 5/13/86
.\"
.TH CHMOD 2 "May 13, 1986"
.UC 4
.SH NAME
chmod \- change mode of file
.SH SYNOPSIS
.nf
.ft B
#include <sys/types.h>
#include <sys/stat.h>

int chmod(const char *\fIpath\fP, mode_t \fImode\fP)
.ig \" You never know
.PP
.ft B
int fchmod(int \fIfd\fP, mode_t \fImode\fP)
..
.fi
.SH DESCRIPTION
The file whose name
is given by \fIpath\fP
.ig
or referenced by the descriptor
.I fd
..
has its mode changed to
.IR mode .
Modes are constructed by
.IR or 'ing
together some
combination of the following, defined in
.IR <sys/stat.h> :
.PP
.RS
.nf
.ta \w'S_ISUID\ \ 'u +\w'04000\ \ \ 'u
S_ISUID	04000	set user ID on execution
S_ISGID	02000	set group ID on execution
S_ISVTX	01000	`sticky bit' (see below)
S_IRWXU	00700	read, write, execute by owner
S_IRUSR	00400	read by owner
S_IWUSR	00200	write by owner
S_IXUSR	00100	execute (search on directory) by owner
S_IRWXG	00070	read, write, execute by group
S_IRGRP	00040	read by group
S_IWGRP	00020	write by group
S_IXGRP	00010	execute (search on directory) by group
S_IRWXO	00007	read, write, execute by others
S_IROTH	00004	read by others
S_IWOTH	00002	write by others
S_IXOTH	00001	execute (search on directory) by others
.fi
.RE
.PP
If mode ISVTX (the `sticky bit') is set on a directory,
an unprivileged user may not delete or rename
files of other users in that directory.  (Minix-vmd)
.PP
Only the owner of a file (or the super-user) may change the mode.
.PP
Writing or changing the owner of a file
turns off the set-user-id and set-group-id bits
unless the user is the super-user.
This makes the system somewhat more secure
by protecting set-user-id (set-group-id) files
from remaining set-user-id (set-group-id) if they are modified,
at the expense of a degree of compatibility.
.SH "RETURN VALUE
Upon successful completion, a value of 0 is returned.
Otherwise, a value of \-1 is returned and
.B errno
is set to indicate the error.
.SH "ERRORS
.B Chmod
will fail and the file mode will be unchanged if:
.TP 15
[ENOTDIR]
A component of the path prefix is not a directory.
.TP 15
[ENAMETOOLONG]
The path name exceeds PATH_MAX characters.
.TP 15
[ENOENT]
The named file does not exist.
.TP 15
[EACCES]
Search permission is denied for a component of the path prefix.
.TP 15
[ELOOP]
Too many symbolic links were encountered in translating the pathname.
(Minix-vmd)
.TP 15
[EPERM]
The effective user ID does not match the owner of the file and
the effective user ID is not the super-user.
.TP 15
[EROFS]
The named file resides on a read-only file system.
.TP 15
[EFAULT]
.I Path
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.
.ig
.PP
.I Fchmod
will fail if:
.TP 15
[EBADF]
The descriptor is not valid.
.TP 15
[EROFS]
The file resides on a read-only file system.
.TP 15
[EIO]
An I/O error occurred while reading from or writing to the file system.
..
.SH "SEE ALSO"
.BR chmod (1),
.BR open (2),
.BR chown (2),
.BR stat (2).
.SH NOTES
The sticky bit was historically used to lock important executables into
memory.