Inotifyd: Difference between revisions
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Sometimes we need to monitor a directory (or file) and do some post processing/actions. Instead of polling the directory for changes we can use inotify to watch a specific folder or file and be notified if something happens within its context. While there are tools in aports designed around inotify (inotify-tools) alpine has a build in tool called inotifyd (part of busybox) to execute a command on file system events. Below is an example of how you can setup a watch folder with just base alpine (busybox and openrc). | Sometimes we need to monitor a directory (or file) and do some post processing/actions. Instead of polling the directory for changes we can use inotify to watch a specific folder or file and be notified if something happens within its context. While there are tools in aports designed around inotify (inotify-tools) alpine has a build in tool called inotifyd (part of busybox) to execute a command on file system events. Below is an example of how you can setup a watch folder with just base alpine (busybox and openrc). | ||
== Create an | == Create an OpenRC service script == | ||
< | {{Cat|/etc/init.d/inotifyd|<nowiki>#!/sbin/openrc-run | ||
#!/sbin/openrc-run | |||
command=/sbin/inotifyd | command=/sbin/inotifyd | ||
| Line 19: | Line 18: | ||
checkpath --directory --owner $INOTIFYD_USER --mode 0775 \ | checkpath --directory --owner $INOTIFYD_USER --mode 0775 \ | ||
/var/log/$RC_SVCNAME | /var/log/$RC_SVCNAME | ||
} | }</nowiki>}} | ||
</ | |||
{{Cat|/etc/conf.d/inotifyd|<nowiki>INOTIFYD_ARGS="/usr/local/bin/myscript /home/username/watchdir:w" | |||
INOTIFYD_USER=username</nowiki>}} | |||
{{Cat|/usr/local/bin/myscript|<nowiki>#!/bin/sh | |||
< | |||
#!/bin/sh | |||
event="$1" | event="$1" | ||
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w) echo "writable $file is closed in $directory";; | w) echo "writable $file is closed in $directory";; | ||
*) echo "This will never happen as we only listen for w.";; | *) echo "This will never happen as we only listen for w.";; | ||
esac | esac</nowiki>}} | ||
</ | |||
== Finishing up == | == Finishing up == | ||
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Starting inotifyd: | Starting inotifyd: | ||
{{Cmd|rc-service inotifyd start}} | {{Cmd|# rc-service inotifyd start}} | ||
Now copy some file into the watch folder and check the service log in /var/log/inotifyd | Now copy some file into the watch folder and check the service log in {{Path|/var/log/inotifyd}}. | ||
In the example above we only listen for file closed events (w). In case you want to listen to more events you can just add them after each other. In case you want to listen to all of them you simply remove all appending event letters from the directory. | In the example above we only listen for file closed events (w). In case you want to listen to more events you can just add them after each other. In case you want to listen to all of them you simply remove all appending event letters from the directory. | ||
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d Subfile is deleted | d Subfile is deleted | ||
</pre> | </pre> | ||
[[Category:Monitoring]] | |||
Latest revision as of 19:52, 1 June 2023
Use case
Sometimes we need to monitor a directory (or file) and do some post processing/actions. Instead of polling the directory for changes we can use inotify to watch a specific folder or file and be notified if something happens within its context. While there are tools in aports designed around inotify (inotify-tools) alpine has a build in tool called inotifyd (part of busybox) to execute a command on file system events. Below is an example of how you can setup a watch folder with just base alpine (busybox and openrc).
Create an OpenRC service script
Contents of /etc/init.d/inotifyd
#!/sbin/openrc-run
command=/sbin/inotifyd
command_args="$INOTIFYD_ARGS"
command_user="$INOTIFYD_USER"
pidfile=/run/${RC_SVCNAME}.pid
command_background=yes
start_stop_daemon_args="--stdout /var/log/$RC_SVCNAME/${RC_SVCNAME}.log --stderr /var/log/$RC_SVCNAME/${RC_SVCNAME}.log"
start_pre() {
checkpath --directory --owner $INOTIFYD_USER --mode 0775 \
/var/log/$RC_SVCNAME
}
Contents of /etc/conf.d/inotifyd
INOTIFYD_ARGS="/usr/local/bin/myscript /home/username/watchdir:w"
INOTIFYD_USER=username
Contents of /usr/local/bin/myscript
#!/bin/sh
event="$1"
directory="$2"
file="$3"
# run some command based on an event
case "$event" in
w) echo "writable $file is closed in $directory";;
*) echo "This will never happen as we only listen for w.";;
esac
Finishing up
Starting inotifyd:
# rc-service inotifyd start
Now copy some file into the watch folder and check the service log in /var/log/inotifyd.
In the example above we only listen for file closed events (w). In case you want to listen to more events you can just add them after each other. In case you want to listen to all of them you simply remove all appending event letters from the directory.
Possible inotify Events
Events:
a File is accessed
c File is modified
e Metadata changed
w Writable file is closed
0 Unwritable file is closed
r File is opened
D File is deleted
M File is moved
u Backing fs is unmounted
o Event queue overflowed
x File can't be watched anymore
If watching a directory:
y Subfile is moved into dir
m Subfile is moved out of dir
n Subfile is created
d Subfile is deleted