[snmp.service] remove snmp.timer unit

[stepanblyschak]

Signed-off-by: Stepan Blyschak stepanb@mellanox.com

- What I did
Removed snmp.timer unit. Trying to address #2750 by removing snmp.timer systemd unit and adding synchronization between counters and SNMP counter dependent MIBs

NOTE: This change depends on sonic-net/sonic-snmpagent#105

- How I did it
Removed snmp.timer unit

- How to verify it
SNMP ansible test;
Mannual test:

• system cold reboot
• system warm reboot
• snmp service restart
• swss service restart

- Description for the changelog
Removed snmp.timer unit

- A picture of a cute animal (not mandatory but encouraged)

[qiluo-msft]

The root cause is that snmp.service Requires swss.service. According to man systemd.unit

Requires=
   Configures requirement dependencies on other units. If this unit gets activated, the units listed here will be activated as well. If one of the other units gets deactivated or its
   activation fails, this unit will be deactivated.

The right option should be

Requisite=
   Similar to Requires=. However, if the units listed here are not started already, they will not be started and the transaction will fail immediately.

[qiluo-msft]

As comment

[yxieca]

@qiluo-msft is there a need for snmp service to be restarted if swss is restarted? Required will serve this purpose but requisite might not.

[qiluo-msft]

Required will serve this purpose but requisite might not.

This is not true in my test.

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In reply to: 482775740 [](ancestors = 482775740)

[jleveque]

I do not have experience with the Requisite= option, but from the description, it seems as though it may be the proper fix here. As long as the SNMP service still starts, stops and restarts when SwSS does, it is the proper fix.

[stepanblyschak]

@qiluo-msft @yxieca @jleveque Thanks! I created a separate PR #2790 for this change,
Keeping this PR open for now, because it is a try to remove a timer and add synchronization