How to setup incrond ( inotify + cron ) to trigger job whenever file got changed.

This post just show you install incron on CentOS ( / Ubuntu ) and trigger file call reverse.sh.

Deploy incrond

Install incrond for CentOS7

First we will need to install incron: ( Cent OS and Ubuntu )

$ sudo yum install incron

$ sudo apt-get install incron

PS if your CentOS can't find the incron repo, try as below.

Type the following command as root user to install repo:
# rpm -Uvh https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm

OR use the following command:
# yum install epel-release.noarch

Make sure we set it to start on reboot:

$ sudo chkconfig incrond on

And now to start incron:

$ sudo service incrond start

Configure incron

# incrontab -l
no table for root

# vi /etc/incron.conf
Add first systoles
# system_table_dir = /var/spool/incron.systables
system_table_dir = /etc/incron.d/proxy.systable

Add Second editor
# editor = nano
editor = vi

Adding reverse.sh from resource folder in this repo

• I put the reverse.sh under /tmp/
• a is your proxy-server.conf location and b is your proxy-server.conf.bak full path.
• I detect md5 change and wait 60 seconds

# vi /tmp/reverse.sh
a="/etc/swift/proxy-server.conf"
echo $a
b="$a.bak"
echo $b
...
sleep 60s

Adding incron monitor file and execution script locaiton

# incrontab -e for adding the line as below
/etc/swift/proxy-server.conf IN_MODIFY /tmp/reverse.sh
# incrontab -e
table updated

# incrontab -l
/etc/swift/proxy-server.conf IN_MODIFY /tmp/reverse.sh

Trouble Shoot, whenever /etc/swift/proxy-server.conf changes, incron will trigger /tmp/reverse.sh

# tail -f /var/log/cron
May 30 11:01:46 JW-swift-demo-proxyonly incrond[24117]: (root) CMD (/opt/ss/support/reverse.sh)