https://www.cisco.com/c/en/us/td/docs/ios/fundamentals/command/reference/cf_book/cf_l1.html logging synchronous To synchronize unsolicited messages and debug output with solicited Cisco IOS software output and prompts for a specific console port line, auxiliary port line, or vty, use the logging synchronous command in line configuration mode. To disable synchronization of unsolicited messages and debug output, use the no form of this command. logging synchronous [level severity-level | all] [limit number-of-lines]