Remove flockfile for tedge_agent before running --init in postint script

[rina23q]

Proposed changes

tedge_agent is supposed to run by the tedge user, therefore, the flockfile is owned by the tedge user. However, due to the directory creation of /var/tedge, tedge_agent --init must be run as root in the postinst script. If the flockfile owned by tedge user exists, the tedge_agent --init will fail.

To fix this issue, the postinst script should remove the flock file if it exists before the initialization.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Improvement (general improvements like code refactoring that doesn't explicitly fix a bug or add any new functionality)
• Documentation Update (if none of the other choices apply)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Paste Link to the issue

#1551

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA (in all commits with git commit -s)
• I ran cargo fmt as mentioned in CODING_GUIDELINES
• I used cargo clippy as mentioned in CODING_GUIDELINES
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

[didier-wenzek]

But then, we will have a lock own by root, preventing the agent to run as tedge. Am I missing something?

[rina23q]

My experiment on my laptop, tedge_agent.lock is gone after tedge_agent --init. However, to keep it safe, I can add the lines to remove /run/lock/tedge_agent.lock after tedge_agent --init.

         if [ -f "/run/lock/tedge_agent.lock" ]; then
                rm /run/lock/tedge_agent.lock
         fi

This was the output when I ran sudo tedge_agent --init.

rina@SAG-CFPPNV2-U:/etc/tedge$ inotifywait -m /run/lock/
Setting up watches.
Watches established.
/run/lock/ CREATE tedge_agent.lock
/run/lock/ OPEN tedge_agent.lock
/run/lock/ CLOSE_WRITE,CLOSE tedge_agent.lock
/run/lock/ DELETE tedge_agent.lock

rina@SAG-CFPPNV2-U:~$ sudo tedge_agent --init
[sudo] password for rina: 
2022-11-04T13:18:47.710656337Z  INFO flockfile::unix: Lockfile created "/run/lock/tedge_agent.lock"
2022-11-04T13:18:47.710699697Z  INFO tedge_agent::agent: tedge_agent starting
2022-11-04T13:18:47.712704417Z  INFO sm-agent{config_dir="/etc/tedge"}: tedge_agent::agent: Initializing the tedge agent session

[didier-wenzek]

Okay. It makes sense and it's useless to remove the lock after --init.

[didier-wenzek]

Approved