用于监视新文件目录的bash脚本

Question

It's important to note immediately there are many variations of the 'script to watch a directory' I realize inotify-tools would be ideal however this particular script is being used to monitor a vboxsf filesystem which unfortunately doesn't forward filesystem notifications. This script is a hack to refresh a file so a separate running daemon will notice it.

The script below is a compromise. I spent a long time dealing with various issues

1. the correct find args
2. the find path and
3. the timing for touching the found file.

The objective is to identify the new file, touch it so the separate running daemon notices it and subsequently processes it. The problem is, well, it gobbles cpu and presumably from the find. I'd like help in finding a more efficient way of doing this.

Although not necessary, but to fully test, one would need a mounted vboxsf filesystem with inotifywait running like so inotifywait -m /watches/watchdir -e attrib

File creation on the host side will not result in an ATTRIB notification on the guest side until the file is somehow refreshed -- in which case this hack uses ' touch '

thedir=/watches/watchdir

touch_me() {
    if [ "${newbie}" ]; then
 #  echo "got this: ${newbie}"
    touch -d '-120 seconds' "${newbie}"
    fi
}

while true
do
    newbie=`find $thedir/* -type f -mmin 0.1 2>/dev/null`
    touch_me
done

Answer 1

The filesystem's type at host side is not vboxsf , I believe.

As a consequence, inotify-tools can be used at the host server side, right?

It is assumed that a touch on the newly created file from host server side has no effect, rigth?

When new files are created at host server side, inotify-tools could use VBoXManage to execute a touch command into the guest, eg:

$ VBoxManage guestcontrol execute vmname /usr/bin/touch --username root --password 'changeme' --arguments "-d '-120 seconds' /watches/watchdir/${newbie}"

What do you think?

Otherwise your script is ok, but it is using polling. So maybe a sleep is mandatory in such situation, with the risk to miss some of the newly created files...

Answer 2

a tool like sysdig may be helpful. For example, the following command show every file open that happens in /tmp:

sysdig evt.type=open and fd.name contains /tmp

This tool is very complex yet powerful, and by reading its manual you may find a valid solution to your problem.

Answer 3

the loop is running continually without the need to do so

find $thedir/* -type f -mmin 0.1

will find files changed no more the 6 seconds ago (and no more then 55 seconds in the future but unlikely to occur naturally). Supposing find runs in less the a second (unless you have thousands of files) you might like to insert a sleep 5 in the loop. Another thing is why do you put the time back 2 minutes on the recently changed files that you find ... surely anything that has not been changed for 2 minutes is in the same condition. Would in not be a better option to mark the file with a rarely used attribute like 'no dump' so that the other demon is not going to unintentionally on files that look like they were touched by the script but were not ?

Rather then looping intensively with find would it be an option to do something like this (leaving the touch_me to to the -2min for the other deamon to detect):

touch_me() {
  #  echo "got this: $1"
  touch -d '-120 seconds' $1
}

touch /tmp/file.ref
while true
do
  for FILE in $thedir/*
  do
    [ $FILE -nt /tmp/file.ref ] && touch_me $FILE
  done
  touch /tmp/file.ref
  sleep 60
done

This way each iteration of the while will look for files that have been modified after the previous iteration.