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In Unix-like operating systems, a sticky bit is a permission bit which is set on a file or folder, thereby permitting only the owner or root user of the file or folder to modify, rename or delete the concerned directory or file. No other user would be permitted to have these privileges on a file which has a sticky bit. In Unix-like systems, without the sticky bit on, any user can modify, rename or delete the directory or file regardless of the owner of the file or folder.
Introduced in the fifth edition of Unix, the sticky bit was created for only pure executable files. When introduced, files with a sticky bit ensured the text segment of the executable application was available in swap space even after the exit of the process. This allows the speeding up of executions of the frequently used executable programs. Presently, this feature has been abandoned by many and is only retained in Unixware and HP-UX.
The sticky bit is mostly used on the folders residing within file systems inside Unix-like operating systems. When the sticky bit is set, the filesystem treats such files or directories in a unique way that only the owner or the root owner can have rights of modifying, deleting or renaming of these. In Solaris-like operating systems, when the sticky bit is set on non-executable files, the files are not cached by the kernel. This helps not only to avoid allowing access to these files, but also helps in flushing important data from the system cache with respect to the files. In some cases, a sticky bit is also used for indicating that a particular file is yet to be mounted, thus allowing programs to ignore unmounted files.