inotify (inode notify) is aLinux kernel subsystem created by John McCutchan, which monitors changes to thefilesystem, and reports those changes to applications. It can be used to automatically update directory views, reload configuration files, log changes, backup, synchronize, and upload. Theinotifywait andinotifywatch commands (maintained by Eric Curtin as part of the inotify-tools project) allow using the inotify subsystem from the command line.[1] One major use is indesktop search utilities likeBeagle, where its functionality permitsreindexing of changed files without scanning the filesystem for changes every few minutes, which would be very inefficient.
inotify replaced an earlier facility,dnotify, which had similar goals. Inotify was merged into theLinux kernel mainline in kernel version 2.6.13, released on August 29, 2005;[2] later kernel versions included further improvements. The required library interfaces were added into theGNU C Library (glibc) in its version 2.4, released in March 2006, while the support for inotify was completed in glibc version 2.5, released in September 2006.[3]
Limitations imposed by inotify include the following:
There are a number of advantages when using inotify when compared to the olderdnotify API that it replaced.[7][8][9] With dnotify, a program had to use onefile descriptor for each directory that it was monitoring. This can become a bottleneck since the limit of file descriptors per process could be reached. Later, fanotify was created to overcome this issue. The use of file descriptors along with dnotify also proved to be a problem when using removable media. Devices could not be unmounted since file descriptors kept the resource busy.
Another drawback of dnotify is the level of granularity, since programmers can only monitor changes at the directory level. To access detailed information about the environmental changes that occur when a notification message is sent, a stat structure must be used; this is considered a necessary evil in that a cache of stat structures has to be maintained, for every new stat structure generated a comparison is run against the cached one.
The inotify API uses fewer file descriptors, allowing programmers to use the established select and poll interface, rather than the signal notification system used bydnotify. This also makes integration with existing select- or poll-based libraries (likeGLib) easier.
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