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After cloud-init runs a user data script on the first boot of an EC2 instance, a state file is presumably written so that cloud-init won't run the script again on subsequent reboots. There are cases where I'd like to delete this state file so that the user data script will run again. Where is it?

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rm /var/lib/cloud/instances/*/sem/config_scripts_user

Confirmed working on:

  • CentOS 7.4
  • Ubuntu 14.04
  • Ubuntu 16.04

For the sake of completeness, if you have a situation where you care to keep track of the fact/possibility that this AMI [had a parent AMI that ...] and they all ran cloud-init user data, you can delete only the current semaphore.

rm /var/lib/cloud/instance/sem/config_scripts_user

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    You figured that out quickly. – c24w Jun 1 '17 at 9:19
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    @c24w Those timestamps are misleading. It actually took me a few hours of research and testing, so once I figured it out, I created this question to help the next person looking for a definitive answer. – Mike Conigliaro Jun 1 '17 at 17:21
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    I've come across this since and didn't realise it was encouraged to post wiki-type Q&As. Appreciate you documenting this! – c24w Jun 8 '17 at 20:11
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    I'm glad this was encouraged on serverfault. I've seen it downvoted many times on SO – Nathan Apr 11 '18 at 16:51
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    In addition to @Mike Conigliaro response, in order to delete only the running one semaphore: rm /var/lib/cloud/instances/$(curl -s 169.254.169.254/latest/meta-data/instance-id)/sem/… – NicoKowe Jul 13 '18 at 14:39
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You can also configure your user data to re-run on every boot, instead of removing the state file. You have to use cloud_final_modules in your userdata script to re-run the userdata script and for that you have to customise uderdata to have miultiple files in userdata. Example userdata file would be like:

Content-Type: multipart/mixed; boundary="//"
MIME-Version: 1.0

--//
Content-Type: text/cloud-config; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="cloud-config.txt"

#cloud-config
cloud_final_modules:
- [scripts-user, always]

--//
Content-Type: text/x-shellscript; charset="us-ascii"
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment; filename="userdata.txt"

#!/bin/bash
/bin/echo "Hello World" >> /tmp/userdata-test.txt
--//

This will make userdata script to execute on last step of every boot process. Here only a single line bin/echo "Hello World" >> /tmp/userdata-test.txt to be executed, replace this with your shell script that needs to be executed every time a machine is booted.

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    Note: if are replacing an existing user script on an instance, you may need to run cloud-init clean on the instance before the new user-data script will execute. – crockeea Mar 27 '20 at 0:50
  • This method is documented by AWS here serverfault.com/questions/797482/… – comfytoday Oct 14 '20 at 1:02
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You can put your script in /etc/rc.local, which will run the script on every reboot.

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    /etc/rc.local has nothing to do with EC2 user data. – Mike Conigliaro May 1 '17 at 20:07
  • @MikeConigliaro I wanted to use user-data to make something run on every boot, so I made the user-data script append it to /etc/rc.local. – user253751 Oct 1 '17 at 2:37

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