1. 什么是inotify
Inotify API提供了一种监视文件系统的机制事件。 Inotify可用于监视单个文件或监视目录。当监视目录时，Inotify将返回目录本身的事件，以及内部的文件目录。
简单的说，就是inotify可以为你监控文件系统的变化，在发生一些事件时通知你。
2. 实验
需要安装inotify-tools包
# arch系统
yay -S inotify-tools
inotify-tools提供了两个命令：inotifywait和inotifywatch
2.1 inotifywait
先来看inotifywait,它被用来"Wait for a particular event on a file or set of files.", 也就是说等待在文件上的某些事件发生。使用inotifywait -h查看其支持的参数：
-h show this help info
--exclude <pattern> 排除匹配所给正则的所有事件
--excludei <pattern> 类似前一个命令但非敏感
--include <pattern> 排除除匹配正则之外的所有事件
--includei <pattern> 类似前一个命令但非敏感
-m|--monitor 在timeout之前保持监听，若不设置此标志，inotifywait将在一个事件后退出。
-d|--daemon 类似前一个命令但在后台运行，将日志输出到`--outfile`所指定的文件
-P|--no-dereference 不跟踪符号链接
-r|--recursive 递归的监听、
--fromfile <file> Read files to watch from <file> or `-' for stdin.
-o|--outfile <file> 输出到<file>而不是标准输出
-s|--syslog 向syslog发送错误而不是Stderr
-q|--quiet 只输出事件
-qq 啥也不输出
--format <fmt> 以特定格式输出
--no-newline 在格式化输出后不打印换行符
--timefmt <fmt> strftime-compatible format string for use with
%T in --format string.
-c|--csv 以csv格式输出
-t|--timeout <seconds> 当监听一个事件时，在<seconds>秒后超时
-e|--event <event1> 监听特定事件，若不设置，则监听所有事件
支持的event有：
Events:
access file or directory contents were read
modify file or directory contents were written
attrib file or directory attributes changed
close_write file or directory closed, after being opened in
writable mode
close_nowrite file or directory closed, after being opened in
read-only mode
close file or directory closed, regardless of read/write mode
open file or directory opened
moved_to file or directory moved to watched directory
moved_from file or directory moved from watched directory
move file or directory moved to or from watched directory
move_self A watched file or directory was moved.
create file or directory created within watched directory
delete file or directory deleted within watched directory
delete_self file or directory was deleted
unmount file system containing file or directory unmounted
在终端1中：
mkdir ~/inotify-demo && cd inotify-demo # 建立测试文件夹
inotifywait -rmc -q .
在终端2中：
cd ~/inotify-demo
touch aa.txt
此时切换到终端1，可以看到事件输出：
...
./,CREATE,aa.txt
./,OPEN,aa.txt
./,ATTRIB,aa.txt
./,"CLOSE_WRITE,CLOSE",aa.txt
./,"OPEN,ISDIR",
./,"CLOSE_NOWRITE,CLOSE,ISDIR",
./,OPEN,aa.txt
./,"CLOSE_NOWRITE,CLOSE",aa.txt
打开文件aa.txt，写入一行
inotify-demo
可看到终端1中也已将事件打印出：
...
./,CREATE,4913
./,OPEN,4913
./,ATTRIB,4913
./,"CLOSE_WRITE,CLOSE",4913
./,DELETE,4913
./,MOVED_FROM,aa.txt
./,CREATE,aa.txt
./,OPEN,aa.txt
./,MODIFY,aa.txt
./,MODIFY,aa.txt
./,ATTRIB,aa.txt
./,"CLOSE_WRITE,CLOSE",aa.txt
./,ATTRIB,aa.txt
./,"OPEN,ISDIR",
./,"CLOSE_NOWRITE,CLOSE,ISDIR",
将所有的事件都打印出略显杂乱，这里我们只让其监听modify事件
inotifywait -rmc -q -e modify .
创建文件bb.txt
touch bb.txt
可观察到，未有任何事件被打印。
在bb.txt中写入一行inotify-demo
可观察到事件打印：
./,MODIFY,bb.txt
./,MODIFY,bb.txt
2.2 inotifywatch
inotifywatch被用于收集文件系统使用信息
其命令参数和inotifywait大致相同，可使用inotifywatch查看
实验：
cd ~/inotify-demo
# 在30秒内监听crate,modify,delete三个事件，在30秒结束后打印统计信息
inotifywatch -v -e create -e modify -e delete -t 30 -r .
接下来30秒，创建了4个文件，修改了2个文件，删除了1个文件
事件统计信息为:
Establishing watches...
Setting up watch(es) on .
OK, . is now being watched.
Total of 1 watches.
Finished establishing watches, now collecting statistics.
Will listen for events for 30 seconds.
total modify create delete filename
15 4 8 3 ./
TODO：统计信息与实际操作有所不符，目前不清楚为啥
3. 使用golang调用inotify
package main
import (
"log"
"github.com/fsnotify/fsnotify"
)
func main() {
watcher, err := fsnotify.NewWatcher()
if err != nil {
log.Fatal(err)
}
defer watcher.Close()
done := make(chan bool)
go func() {
for {
select {
case event, ok := <-watcher.Events:
if !ok {
return
}
log.Println("event:", event)
if event.Op&fsnotify.Write == fsnotify.Write {
log.Println("modified file:", event.Name)
}
case err, ok := <-watcher.Errors:
if !ok {
return
}
log.Println("error:", err)
}
}
}()
err = watcher.Add("/tmp/foo")
if err != nil {
log.Fatal(err)
}
<-done
}
References
https://juejin.cn/post/6988561056364757022
https://www.infoq.cn/article/inotify-linux-file-system-event-monitoring