NAME
sticky —
sticky text and append-only
directories
DESCRIPTION
A special file mode, called the sticky bit (mode S_ISVTX), is used to indicate special treatment for shareable executable files and directories. See chmod(2) or the file /usr/include/sys/stat.h for an explanation of file modes.
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.
Sharable executable files are created with the
-n and -z options of the
loader ld(1).
Only the super-user can set the sticky bit on a sharable executable file.
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 /tmp which must be publicly writable but should deny users the license to arbitrarily delete or rename each others' files.
Any user may create a sticky directory. See chmod(1) for details about modifying file modes.
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.
Neither open(2) nor mkdir(2) will create a file with the sticky bit set.
HISTORY
A sticky command appeared in Version 32V
AT&T UNIX.