sticky.8

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)sticky.8	3.2	7/13/88
.TH sticky 8 RISC
.SH Name
sticky \- executable files with persistent text
.SH Description
.NXR "file" "sharing executable"
.NXR "sticky file" "removing"
The sticky bit (file mode bit 01000),
is used to indicate special treatment
for certain executable files and directories.
.PP
While the sticky bit, mode 01000
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.
As long as a copy remains in the swap area, the
original text cannot be overwritten in the file system,
nor can the file be deleted.
Directory entries can be removed so long as one link remains.
.PP
Sharable files are made by the
.PN \-n
and
.PN \-z
options of
.MS ld 1 .
.PP
To replace a sticky file that has been used,
clear the sticky bit with
.PN chmod
and execute the old program to flush the swapped copy.
This can be done safely even if others are using it.
Overwrite the sticky file.
If the file is being executed by any process,
writing will be prevented.  It suffices to simply remove the file
and then rewrite it, being careful to reset the owner and mode with
.PN chmod
and
.PN chown .
Set the sticky bit again.
.PP 
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 superuser.  This feature is usefully applied to directories such 
as 
.PN /tmp 
which must be publicly writeable
but should deny users the license to arbitrarily delete or rename each 
others' files.
.SH Restrictions
Only the superuser can set the sticky bit.
.SH See Also
chmod(2)