1.\" $OpenBSD: sticky.8,v 1.5 2000/12/22 16:54:38 avsm Exp $ 2.\" $NetBSD: sticky.8,v 1.3 1994/11/30 19:36:27 jtc Exp $ 3.\" 4.\" Copyright (c) 1980, 1991, 1993 5.\" The Regents of the University of California. All rights reserved. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. All advertising materials mentioning features or use of this software 16.\" must display the following acknowledgement: 17.\" This product includes software developed by the University of 18.\" California, Berkeley and its contributors. 19.\" 4. Neither the name of the University nor the names of its contributors 20.\" may be used to endorse or promote products derived from this software 21.\" without specific prior written permission. 22.\" 23.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 24.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 27.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33.\" SUCH DAMAGE. 34.\" 35.\" @(#)sticky.8 8.1 (Berkeley) 6/5/93 36.\" 37.Dd June 5, 1993 38.Dt STICKY 8 39.Os 40.Sh NAME 41.Nm sticky 42.Nd sticky text and append-only directories 43.Sh DESCRIPTION 44A special file mode, called the 45.Em sticky bit 46(mode S_ISVTX), 47is used to indicate special treatment 48for shareable executable files and directories. 49See 50.Xr chmod 2 51or 52the file 53.Pa /usr/include/sys/stat.h 54for an explanation of file modes. 55.Sh STICKY TEXT EXECUTABLE FILES 56An executable shareable file whose sticky bit is set 57will not be immediately discarded from swap space after execution. 58The kernel will hoard the text segment of the file for future 59reuse and avoid having to reload the program. 60Shareable text segments are normally placed 61in a least-frequently used cache after use, 62and thus the `sticky bit' has little effect on commonly used text images. 63.Pp 64Sharable executable files are created with the 65.Fl n 66and 67.Fl z 68options of 69the loader 70.Xr ld 1 . 71.Pp 72Only the superuser can set the sticky bit 73on a sharable executable file. 74.Sh STICKY DIRECTORIES 75A directory whose `sticky bit' is set 76becomes an append-only directory, or, more accurately, 77a directory in which the deletion of files is restricted. 78A file in a sticky directory may only be removed or renamed 79by a user if the user has write permission for the directory and 80the user is the owner of the file, the owner of the directory, 81or the superuser. 82This feature is usefully applied to directories such as 83.Pa /tmp 84which must be publicly writable but 85should deny users the license to arbitrarily 86delete or rename each others' files. 87.Pp 88Any user may create a sticky directory. 89See 90.Xr chmod 1 91for details about modifying file modes. 92.Sh BUGS 93Since the text areas of sticky text executables are stashed in the swap area, 94abuse of the feature can cause a system to run out of swap. 95.Pp 96Neither 97.Xr open 2 98nor 99.Xr mkdir 2 100will create a file with the sticky bit set. 101.Sh HISTORY 102A 103.Nm 104command appeared in Version 32V AT&T UNIX. 105