MySQL5.7.18 tar压缩包安装到CentOS7上后默认没有my.cnf配置文件的，此时可以正常启动，正常访问数据库。但是将配置文件放到/etc/my.cnf处后，MySQL就无法启动了，提示pid文件不存在
Starting MySQL.. ERROR! The server quit without updating PID file (/usr/local/mysql/data/mysql.pid).
/usr/local/mysql/data/mysql.pid是我在my.cnf中定义的pid-file
该配置文件可在CentOS6中的MySQL5.6.36正常使用。
当我再次删除配置后，mysql又可以正常启动，可以在/usr/local/mysql/data目录下看到localhost.localdomain.pid文件。
为什么添加配置文件后反而不生成pid文件了？如果不使用配置文件又该如何控制MySQL性能？
查看一下mysql的log日志，你的配置文件语法是否有问题，导致启动的时候读取错误了
注意文件夹权限，你的pid目录没有写的权限
不知道是什么原因，MySQL5.8.17没有这项配置了innodb_additional_mem_pool_size，不确定是否有替代项。
可以用mysql> show global variables like '%log%';查询全局信息
+-----------------------------------------+--------------------------------+
| Variable_name | Value |
+-----------------------------------------+--------------------------------+
| back_log | 30 |
| binlog_cache_size | 32768 |
| binlog_checksum | CRC32 |
| binlog_direct_non_transactional_updates | OFF |
| binlog_error_action | IGNORE_ERROR |
| binlog_format | STATEMENT |
| binlog_gtid_simple_recovery | OFF |
| binlog_max_flush_queue_time | 0 |
| binlog_order_commits | ON |
| binlog_row_image | FULL |
| binlog_rows_query_log_events | OFF |
| binlog_stmt_cache_size | 32768 |
| binlogging_impossible_mode | IGNORE_ERROR |
| expire_logs_days | 0 |
| general_log | ON |
| general_log_file | /usr/local/mysql/log/mysql.log |
| innodb_api_enable_binlog | OFF |
| innodb_flush_log_at_timeout | 1 |
| innodb_flush_log_at_trx_commit | 1 |
| innodb_locks_unsafe_for_binlog | OFF |
| innodb_log_buffer_size | 1048576 |
| innodb_log_compressed_pages | ON |
| innodb_log_file_size | 33554432 |
| innodb_log_files_in_group | 2 |
| innodb_log_group_home_dir | ./ |
| innodb_mirrored_log_groups | 1 |
| innodb_online_alter_log_max_size | 134217728 |
| innodb_undo_logs | 128 |
| log_bin | OFF |
| log_bin_basename | |
| log_bin_index | |
| log_bin_trust_function_creators | OFF |
| log_bin_use_v1_row_events | OFF |
| log_error | /usr/local/mysql/log/error.log |
| log_output | FILE |
| log_queries_not_using_indexes | OFF |
| log_slave_updates | OFF |
| log_slow_admin_statements | OFF |
| log_slow_slave_statements | OFF |
| log_throttle_queries_not_using_indexes | 0 |
| log_warnings | 1 |
| max_binlog_cache_size | 18446744073709547520 |
| max_binlog_size | 1073741824 |
| max_binlog_stmt_cache_size | 18446744073709547520 |
| max_relay_log_size | 0 |
| relay_log | |
| relay_log_basename | |
| relay_log_index | |
| relay_log_info_file | relay-log.info |
| relay_log_info_repository | FILE |
| relay_log_purge | ON |
| relay_log_recovery | OFF |
| relay_log_space_limit | 0 |
| simplified_binlog_gtid_recovery | OFF |
| slow_query_log | ON |
| slow_query_log_file | /usr/local/mysql/log/slow.log |
| sql_log_bin | ON |
| sql_log_off | OFF |
| sync_binlog | 0 |
| sync_relay_log | 10000 |
| sync_relay_log_info | 10000 |
+-----------------------------------------+--------------------------------+
61 rows in set (0.00 sec)