sticky.8

早期freebsd实现

.\" Copyright (c) 1980, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)sticky.8	8.1 (Berkeley) 6/5/93
.\"
.Dd June 5, 1993
.Dt STICKY 8
.Os BSD 4
.Sh NAME
.Nm sticky
.Nd sticky text and append-only directories
.Sh DESCRIPTION
A special file mode, called the
.Em sticky bit
(mode S_ISVTX),
is used to indicate special treatment
for shareable executable files and directories.
See
.Xr chmod 2
or
the file
.Pa /usr/include/sys/stat.h
for an explanation of file modes.
.Sh STICKY TEXT EXECUTABLE FILES
An executable shareable file whose sticky bit is set
will not be immediately discarded from swap space after execution.
The kernel will hoard the text segment of the file for future
reuse and avoid having to reload the program.
Shareable text segments are normally placed
in a least-frequently-used cache after use,
and thus the `sticky bit' has little effect on commonly-used text images.
.Pp
Sharable executable files are created with the
.Fl n
and
.Fl z
options of
the loader
.Xr ld 1 .
.Pp
Only the super-user can set the sticky bit
on a sharable executable file.
.Sh STICKY DIRECTORIES
A directory whose `sticky bit' is set
becomes an append-only directory, or, more accurately,
a directory in which the deletion of files is restricted.
A file in a sticky directory may only be removed or renamed
by a user if the user has write permission for the directory and
the user is the owner of the file, the owner of the directory,
or the super-user.
This feature is usefully applied to directories such as
.Pa /tmp
which must be publicly writable but
should deny users the license to arbitrarily
delete or rename each others' files.
.Pp
Any user may create a sticky directory.
See
.Xr chmod 1
for details about modifying file modes.
.Sh BUGS
Since the text areas of sticky text executables are stashed in the swap area,
abuse of the feature can cause a system to run out of swap.
.Pp
Neither
.Xr open 2
nor
.Xr mkdir 2
will create a file with the sticky bit set.
.Sh HISTORY
A
.Nm
command appeared in Version 32V AT&T UNIX.