You can get the following error when you’re switching between users in a Zabbix Agent, but failed to stop the processes first.
zabbix_agentd [8394]: Can't recreate Zabbix semaphores for IPC key 0x7a028449 Semaphore ID 196608. Operation not permitted.
The key will obviously be different on your system. If you’re certain no more processes for the Zabbix Agent are running, you can manually remove the semaphores.
~# ipcrm -m 0x7a028449 ~# ipcrm -S 0x7a028449
And then restart your Zabbix Agent.