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Revision 1.5, Mon Feb 5 14:54:31 2007 UTC (13 years, 8 months ago) by rillig
Mention the word "regular file" more clearly. The term "append-only" directory was misleading.
.\" $NetBSD: sticky.7,v 1.5 2007/02/05 14:54:31 rillig Exp $ .\" .\" 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. 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 February 5, 2007 .Dt STICKY 7 .Os .Sh NAME .Nm sticky .Nd Description of the `sticky' (S_ISVTX) bit functionality .Sh DESCRIPTION A special file mode, called the .Em sticky bit (mode .Dv S_ISVTX ) , is used to indicate special treatment for directories. See .Xr chmod 2 or the file .Pa /usr/include/sys/stat.h .Sh STICKY FILES For regular files, the use of mode .Dv S_ISVTX is reserved and can be set only by the super-user. .Nx does not currently treat regular files that have the sticky bit set specially, but this behavior might change in the future. .Sh STICKY DIRECTORIES A directory whose .Dq sticky bit is set becomes 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 HISTORY The sticky bit first appeared in V7, and this manual page appeared in section 8. Its initial use was to mark sharable executables that were frequently used so that they would stay in swap after the process exited. Sharable executables were compiled in a special way so their text and read-only data could be shared amongst processes. .Xr vi 1 and .Xr sh 1 were such executables. This is where the term .Dq sticky comes from - the program would stick around in swap, and it would not have to be fetched again from the file system. Of course as long as there was a copy in the swap area, the file was marked busy so it could not be overwritten. On V7 this meant that the file could not be removed either, because busy executables could not be removed, but this restriction was lifted in BSD releases. .Pp To replace such executables was a cumbersome process. One had first to remove the sticky bit, then execute the binary so that the copy from swap was flushed, overwrite the executable, and finally reset the sticky bit. .Pp Later, on SunOS 4, the sticky bit got an additional meaning for files that had the bit set and were not executable: read and write operations from and to those files would go directly to the disk and bypass the buffer cache. This was typically used on swap files for NFS clients on an NFS server, so that swap I/O generated by the clients on the servers would not evict useful data from the server's buffer cache. .Sh BUGS Neither .Xr open 2 nor .Xr mkdir 2 will create a file with the sticky bit set.