公司一套系统的同步使用的donotify，不能实现子目录的实时同步，通过查资料，发现inotify可以实现子目录的实时同步，以下为笔记。
一、介绍
Inotify 是文件系统事件监控机制，作为 dnotify 的有效替代。dnotify 是较早内核支持的文件监控机制。Inotify 是一种强大的、细粒度的、异步的机制，它满足各种各样的文件监控需要，不仅限于安全和性能。
inotify 可以监视的文件系统事件包括：
IN_ACCESS，即文件被访问
IN_MODIFY，文件被 write
IN_ATTRIB，文件属性被修改，如 chmod、chown、touch 等
IN_CLOSE_WRITE，可写文件被 close
IN_CLOSE_NOWRITE，不可写文件被 close
IN_OPEN，文件被 open
IN_MOVED_FROM，文件被移走,如 mv
IN_MOVED_TO，文件被移来，如 mv、cp
IN_CREATE，创建新文件
IN_DELETE，文件被删除，如 rm
IN_DELETE_SELF，自删除，即一个可执行文件在执行时删除自己
IN_MOVE_SELF，自移动，即一个可执行文件在执行时移动自己
IN_UNMOUNT，宿主文件系统被 umount
IN_CLOSE，文件被关闭，等同于(IN_CLOSE_WRITE | IN_CLOSE_NOWRITE)
IN_MOVE，文件被移动，等同于(IN_MOVED_FROM | IN_MOVED_TO)
注：上面所说的文件也包括目录。
二、为能在shell下使用inotify特性，需要安装inotify-tools
1、inotify-tools：The general purpose of this package is to allow inotify's features to be used from within shell scripts.
下载地址：http://inotify-tools.sourceforge.net/
编译安装
./configure
make
make install
完成后，注意查看manpage，man inotify 、 man inotifywait
1）inotifywait 仅执行阻塞，等待 inotify 事件。您可以监控任何一组文件和目录，或监控整个目录树(目录、子目录、子目录的子目录等等)。在 shell 脚本中使用 inotifywait。
2）inotifywatch 收集关于被监视的文件系统的统计数据，包括每个 inotify 事件发生多少次。
2、inotify的系统相关参数：
/proc interfaces
The following interfaces can be used to limit the amount of kernel memory consumed by inotify:
/proc/sys/fs/inotify/max_queued_events
The value in this file is used when an application calls inotify_init(2) to set an upper limit on the number of events that can be queued to the corresponding inotify instance. Events in excess of this limit are dropped, but an IN_Q_OVERFLOW event is always generated.
/proc/sys/fs/inotify/max_user_instances
This specifies an upper limit on the number of inotify instances that can be created per real user ID.
/proc/sys/fs/inotify/max_user_watches
This specifies a limit on the number of watches that can be associated with each inotify instance.
3、inotifywait 相关的参数（更多，查看manpage）：
inotifywait
This command simply blocks for inotify events, making it appropriate for use in shell scripts. It can watch any set of files and directories, and can recursively watch entire directory trees.
-m, --monitor
Instead of exiting after receiving a single event, execute indefinitely. The default behaviour is to exit after the first event occurs.
-r, --recursive
Watch all subdirectories of any directories passed as arguments. Watches will be set up recursively to an unlimited depth. Symbolic links are not
traversed. Newly created subdirectories will also be watched.
-q, --quiet
If specified once, the program will be less verbose. Specifically, it will not state when it has completed establishing all inotify watches.
-e , --event
Listen for specific event(s) only. The events which can be listened for are listed in the EVENTS section. This option can be specified more than once. If omitted, all events are listened for. use“，”separate multi events
