STICKY(8)STICKY(8)NAMEsticky - persistent text and append-only directories
DESCRIPTION
The sticky bit (file mode bit 01000, see chmod(2)) is used to indicate
special treatment for certain executable files and directories.
STICKY TEXT EXECUTABLE FILES
While the `sticky bit' is set on a sharable executable file, the text
of that file will not be removed from the system swap area. Thus the
file does not have to be fetched from the file system upon each
execution. 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 made by the -n and -z options of 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.
STICKY SYMBOLIC LINKS
Some file systems (such as autonfsmount(8)) will set the 'sticky bit'
on symbolic links to indicate that the link points to a directory. This
is done to indicate to other programs, such as ls(1) and Workspace,
that they need not read the link to determine whether the link points
to a directory. The advantage is that programs can improve their
performance by avoiding the sometimes time-consuming read of the link.
For example, with autonfsmount(8), a remote NFS filesystem is not
mounted until a sticky symbolic link is read. After the filesystem is
mounted, the sticky bit is turned off and remains off until the
filesystem gets unmounted. This scenario makes Workspace faster
because it doesn't have to read the link unless the NFS filesystem is
already mounted.
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.
4th Berkeley Distribution May 26, 1986 STICKY(8)