STICKY(8)

 (c) 1980 Regents of the University of California.

NAME
sticky - 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 NON-EXECUTABLE FILES
If the sticky bit is set on a file which has none of its execute bits set, then the kernel's buffer cache will not be used for accesses to the file. This can be used on large files (such as swap files for diskless clients) so that accesses to these files will not blow everything else out of the server's cache.

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.