老旧业务系统不清楚是否有SQL在执行？如果你用的云主机，公司也没有DBA，更无法通过mysql_sniffer工具，捕获网卡TCP请求抓包
https://github.com/hcymysql/mysql_sniffer
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那你就用strace命令捕获sql
# 直接跟踪mysqld进程捕获sql
shell> yum install strace -y
shell> strace -T -tt -ff -e trace=file,network -p `pidof mysqld` > strace.log 2>&1或
mysql_pid=$(ps aux | grep mysqld | grep 3306 | awk '{print $2}')
shell> strace -T -tt -ff -e trace=file,network -p $mysql_pid > strace.log 2>&1查看捕获的SQL
shell> egrep -i 'select|insert|update|delete' strace.log
