1.\" Copyright (c) 1980, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" %sccs.include.redist.man% 5.\" 6.\" @(#)sticky.8 8.1 (Berkeley) 06/05/93 7.\" 8.Dd 9.Dt STICKY 8 10.Os BSD 4 11.Sh NAME 12.Nm sticky 13.Nd sticky text and append-only directories 14.Sh DESCRIPTION 15A special file mode, called the 16.Em sticky bit 17(mode S_ISVTX), 18is used to indicate special treatment 19for shareable executable files and directories. 20See 21.Xr chmod 2 22or 23the file 24.Pa /usr/include/sys/stat.h 25for an explanation of file modes. 26.Sh STICKY TEXT EXECUTABLE FILES 27An executable shareable file whose sticky bit is set 28will not be immediately discarded from swap space after execution. 29The kernel will hoard the text segment of the file for future 30reuse and avoid having to reload the program. 31Shareable text segments are normally placed 32in a least-frequently-used cache after use, 33and thus the `sticky bit' has little effect on commonly-used text images. 34.Pp 35Sharable executable files are created with the 36.Fl n 37and 38.Fl z 39options of 40the loader 41.Xr ld 1 . 42.Pp 43Only the super-user can set the sticky bit 44on a sharable executable file. 45.Sh STICKY DIRECTORIES 46A directory whose `sticky bit' is set 47becomes an append-only directory, or, more accurately, 48a directory in which the deletion of files is restricted. 49A file in a sticky directory may only be removed or renamed 50by a user if the user has write permission for the directory and 51the user is the owner of the file, the owner of the directory, 52or the super-user. 53This feature is usefully applied to directories such as 54.Pa /tmp 55which must be publicly writable but 56should deny users the license to arbitrarily 57delete or rename each others' files. 58.Pp 59Any user may create a sticky directory. 60See 61.Xr chmod 1 62for details about modifying file modes. 63.Sh BUGS 64Since the text areas of sticky text executables are stashed in the swap area, 65abuse of the feature can cause a system to run out of swap. 66.Pp 67Neither 68.Xr open 2 69nor 70.Xr mkdir 2 71will create a file with the sticky bit set. 72.Sh HISTORY 73A 74.Nm 75command appeared in Version 32V AT&T UNIX. 76