Unix Power Tools
by Jerry Peek
Protecting Files with the Sticky Bit
Unix directory access permissions say that if a user has write permission on a directory, she can rename or remove files there–even files that don't belong to her. Many newer versions of Unix have a way to stop that. The owner of a directory can set its sticky bit. The only people who can rename or remove any file in that directory are the file's owner, the directory's owner, and the superuser.
Here's an example: the user jerry makes a world-writable
directory and sets the sticky bit (shown as
chmod 1777 sharejerry%
ls -ld sharedrwxrwxrwt 2 jerry ora 32 Nov 19 10:31 share
Other people create files in it. When jennifer tries to remove a file that belongs to ellie, she can't:
ls -ltotal 2 -rw-r--r-- 1 ellie ora 120 Nov 19 11:32 data.ellie -rw-r--r-- 1 jennifer ora 3421 Nov 19 15:34 data.jennifer -rw-r--r-- 1 peter ora 728 Nov 20 12:29 data.peter jennifer%
rm data.elliedata.ellie: 644 mode ?
yrm: data.ellie not removed. Permission denied