6 System Dependencies
Direvent relies on the event monitoring API provided by the
6.1 GNU/Linux systems.
On GNU/Linux the program uses
See monitoring file system events in inotify(7) man page.
The maximum number of watches a user process can have is controlled by
the ‘fs.inotify.max_user_watches’ system variable. Normally it
is set to 8192, which is quite enough for most purposes. However, if
you monitor a big number or directories and/or are using recursive
watchers, you may need to increase this number. In that case, use
sysctl (see configure kernel parameters at
runtime in sysctl(8) man page) to raise the limit, e.g.:
sysctl -w fs.inotify.max_user_watches=16384
Most GNU/Linux distributions provide the file /etc/sysctl.conf which can be used to set this variable on startup.
The following system-dependent events are defined on systems that use
A file was opened.
6.2 BSD systems
When compiled on BSD systems (including Darwin),
kqueue (see kernel event
notification mechanism in kqueue(2) man page).
This interface needs an open file handle for each file in a monitored directory, which means that the number of watchers is limited by the maximum number of open files. Use ‘ulimit -n NUM’ in order to raise it to a higher number.
Since it operates on files,
kqueue does not provide direct
support for the ‘create’ generic event.
over this disadvantage by keeping track of the contents of each
monitored directory and rescanning it each time a ‘WRITE’ system
event is reported for it. It then generates the ‘open’ event for
each file that appeared after the last scan. Such a rescan can
consume considerable time if a directory has a very large number of
files in it.
The following system-dependent events are available:
The file was renamed.
Access to the file was revoked via
revoke()(see revoke file access in revoke(2) man page) or the underlying file system was unmounted.
6.3 Darwin (Mac OS X)
Essentially the same as BSD. The main difference compared to Linux
and BSD is that on Darwin the watchers are set after disconnecting from the
controlling terminal, because Darwin lacks the
rfork call and the
event queue cannot be inherited by the child process.
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