【IT168 技術文檔】公司一套系統的同步使用的donotify，不能實現子目錄的實時同步，通過查資料，發現inotify可以實現子目錄的實時同步，以下為筆記。
一、介紹
Inotify 是文件系統事件監控機制，作為 dnotify 的有效替代。dnotify 是較早內核支持的文件監控機制。Inotify 是一種強大的、細粒度的、異步的機制，它滿足各種各樣的文件監控需要，不僅限於安全和性能。
inotify 可以監視的文件系統事件包括：
IN_ACCESS，即文件被訪問
IN_MODIFY，文件被 write
IN_ATTRIB，文件屬性被修改，如 chmod、chown、touch 等
IN_CLOSE_WRITE，可寫文件被 close
IN_CLOSE_NOWRITE，不可寫文件被 close
IN_OPEN，文件被 open
IN_MOVED_FROM，文件被移走,如 mv
IN_MOVED_TO，文件被移來，如 mv、cp
IN_CREATE，創建新文件
IN_DELETE，文件被刪除，如 rm
IN_DELETE_SELF，自刪除，即一個可執行文件在執行時刪除自己
IN_MOVE_SELF，自移動，即一個可執行文件在執行時移動自己
IN_UNMOUNT，宿主文件系統被 umount
IN_CLOSE，文件被關閉，等同於(IN_CLOSE_WRITE | IN_CLOSE_NOWRITE)
IN_MOVE，文件被移動，等同於(IN_MOVED_FROM | IN_MOVED_TO)
注：上面所說的文件也包括目錄。
二、為能在shell下使用inotify特性，需要安裝inotify-tools
1、inotify-tools：The general purpose of this package is to allow inotify's features to be used from within shell scripts.
下載地址：http://inotify-tools.sourceforge.net/
編譯安裝
./configure
make
make install
完成後，注意查看manpage，man inotify 、 man inotifywait
1）inotifywait 僅執行阻塞，等待 inotify 事件。您可以監控任何一組文件和目錄，或監控整個目錄樹(目錄、子目錄、子目錄的子目錄等等)。在 shell 腳本中使用 inotifywait。
2）inotifywatch 收集關於被監視的文件系統的統計數據，包括每個 inotify 事件發生多少次。
2、inotify的系統相關參數：
/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 相關的參數(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
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
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