Dnotify
Encyclopedia
dnotify is a file system
event monitor for the Linux kernel
, one of the subfeatures of the fcntl call. It was introduced in the 2.4 kernel series. It has been obsoleted by inotify
, but will be retained for compatibility reasons.
Its function is essentially an extension to filesystems to notice changes to the filesystem, and report those changes to applications.
One major use is in desktop search
utilities like Beagle
, where its functionality permits reindexing
of changed files without scanning the filesystem for changes every few minutes, which would be very inefficient. By being told that a file has changed directly by the kernel, rather than actively looking, Beagle and such utilities can achieve change-to-reindexing times of only about a second, with very small performance hits (dnotify therefore enables the use of such programs in a sensible manner; daemon
s are generally not accepted by distributors if they drain system performance noticeably to provide userland functionality.
File system
A file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...
event monitor for the Linux kernel
Linux kernel
The Linux kernel is an operating system kernel used by the Linux family of Unix-like operating systems. It is one of the most prominent examples of free and open source software....
, one of the subfeatures of the fcntl call. It was introduced in the 2.4 kernel series. It has been obsoleted by inotify
Inotify
inotify is a Linux kernel subsystem that acts to extend filesystems to notice changes to the filesystem, and report those changes to applications. It replaces an earlier facility, dnotify, which had similar goals....
, but will be retained for compatibility reasons.
Its function is essentially an extension to filesystems to notice changes to the filesystem, and report those changes to applications.
One major use is in desktop search
Desktop search
Desktop search is the name for the field of search tools which search the contents of a user's own computer files, rather than searching the Internet...
utilities like Beagle
Beagle (software)
Beagle is a search system for Linux and other such modern Unix-like systems, enabling the user to search documents, chat logs, email and contact lists in a similar way to Spotlight in Mac OS X, and Windows Search or Google Desktop under Linux or Microsoft Windows...
, where its functionality permits reindexing
Index (information technology)
In computer science, an index can be:# an integer that identifies an array element# a data structure that enables sublinear-time lookup -Array element identifier:...
of changed files without scanning the filesystem for changes every few minutes, which would be very inefficient. By being told that a file has changed directly by the kernel, rather than actively looking, Beagle and such utilities can achieve change-to-reindexing times of only about a second, with very small performance hits (dnotify therefore enables the use of such programs in a sensible manner; daemon
Daemon (computer software)
In Unix and other multitasking computer operating systems, a daemon is a computer program that runs as a background process, rather than being under the direct control of an interactive user...
s are generally not accepted by distributors if they drain system performance noticeably to provide userland functionality.
See also
- File alteration monitorFile alteration monitorIn computing, the File Alteration Monitor, also known as FAM and sgi_fam, provides a subsystem developed by Silicon Graphics for Unix-like operating systems. The FAM subsystem allows applications to watch certain files and be notified when they are modified...
- GaminGaminGamin is a monitoring system for files and directories that independently implements a subset of FAM, the File Alteration Monitor. Running as a service, it allows for the detection of modifications to a file or directory...
- inotifyInotifyinotify is a Linux kernel subsystem that acts to extend filesystems to notice changes to the filesystem, and report those changes to applications. It replaces an earlier facility, dnotify, which had similar goals....
, a dnotify replacement. - The Documentation/filesystems/dnotify.txt file in the kernel source tree.