问题描述：启动MySQL数据库时报错"Another process with pid 3306 is using unix socket file……"，如下所示：
数据库：MySQL 5.7.21
1、异常重现
2023-09-23T06:09:48.644151Z 0 [Note] Server socket created on IP: '::'.
2023-09-23T06:09:48.645247Z 0 [ERROR] Another process with pid 3306 is using unix socket file.
2023-09-23T06:09:48.645261Z 0 [ERROR] Unable to setup unix socket lock file.
2023-09-23T06:09:48.645266Z 0 [ERROR] Aborting

2023-09-23T06:09:48.645322Z 0 [Note] Binlog end
2023-09-23T06:09:48.646233Z 0 [Note] Shutting down plugin 'rpl_semi_sync_slave'
2023-09-23T06:09:48.646297Z 0 [Note] Shutting down plugin 'rpl_semi_sync_master'
2023-09-23T06:09:48.646327Z 0 [Note] unregister_replicator OK
2023-09-23T06:09:48.646329Z 0 [Note] Shutting down plugin 'ngram'
2023-09-23T06:09:48.646330Z 0 [Note] Shutting down plugin 'partition'
2023-09-23T06:09:48.646332Z 0 [Note] Shutting down plugin 'ARCHIVE'
2023-09-23T06:09:48.646334Z 0 [Note] Shutting down plugin 'BLACKHOLE'
2023-09-23T06:09:48.646336Z 0 [Note] Shutting down plugin 'INNODB_SYS_VIRTUAL'
2023-09-23T06:09:48.646338Z 0 [Note] Shutting down plugin 'INNODB_CHANGED_PAGES'
2023-09-23T06:09:48.646339Z 0 [Note] Shutting down plugin 'INNODB_SYS_DATAFILES'
2023-09-23T06:09:48.646341Z 0 [Note] Shutting down plugin 'INNODB_SYS_TABLESPACES'
2023-09-23T06:09:48.646342Z 0 [Note] Shutting down plugin 'INNODB_SYS_FOREIGN_COLS'
2023-09-23T06:09:48.646344Z 0 [Note] Shutting down plugin 'INNODB_SYS_FOREIGN'
2023-09-23T06:09:48.646345Z 0 [Note] Shutting down plugin 'INNODB_SYS_FIELDS'
2023-09-23T06:09:48.646346Z 0 [Note] Shutting down plugin 'INNODB_SYS_COLUMNS'
2023-09-23T06:09:48.646348Z 0 [Note] Shutting down plugin 'INNODB_SYS_INDEXES'
2023-09-23T06:09:48.646349Z 0 [Note] Shutting down plugin 'INNODB_SYS_TABLESTATS'
2023-09-23T06:09:48.646350Z 0 [Note] Shutting down plugin 'INNODB_SYS_TABLES'
2023-09-23T06:09:48.646352Z 0 [Note] Shutting down plugin 'INNODB_FT_INDEX_TABLE'
2023-09-23T06:09:48.646353Z 0 [Note] Shutting down plugin 'INNODB_FT_INDEX_CACHE'
2023-09-23T06:09:48.646354Z 0 [Note] Shutting down plugin 'INNODB_FT_CONFIG'
2023-09-23T06:09:48.646364Z 0 [Note] Shutting down plugin 'INNODB_FT_BEING_DELETED'
2023-09-23T06:09:48.646366Z 0 [Note] Shutting down plugin 'INNODB_FT_DELETED'
2023-09-23T06:09:48.646367Z 0 [Note] Shutting down plugin 'INNODB_FT_DEFAULT_STOPWORD'
2023-09-23T06:09:48.646369Z 0 [Note] Shutting down plugin 'INNODB_METRICS'
2023-09-23T06:09:48.646370Z 0 [Note] Shutting down plugin 'INNODB_TEMP_TABLE_INFO'
2023-09-23T06:09:48.646372Z 0 [Note] Shutting down plugin 'INNODB_BUFFER_POOL_STATS'
2023-09-23T06:09:48.646373Z 0 [Note] Shutting down plugin 'INNODB_BUFFER_PAGE_LRU'
2023-09-23T06:09:48.646374Z 0 [Note] Shutting down plugin 'INNODB_BUFFER_PAGE'
2023-09-23T06:09:48.646376Z 0 [Note] Shutting down plugin 'INNODB_CMP_PER_INDEX_RESET'
2023-09-23T06:09:48.646377Z 0 [Note] Shutting down plugin 'INNODB_CMP_PER_INDEX'
2023-09-23T06:09:48.646378Z 0 [Note] Shutting down plugin 'INNODB_CMPMEM_RESET'
2023-09-23T06:09:48.646380Z 0 [Note] Shutting down plugin 'INNODB_CMPMEM'
2023-09-23T06:09:48.646381Z 0 [Note] Shutting down plugin 'INNODB_CMP_RESET'
2023-09-23T06:09:48.646382Z 0 [Note] Shutting down plugin 'INNODB_CMP'
2023-09-23T06:09:48.646384Z 0 [Note] Shutting down plugin 'INNODB_LOCK_WAITS'
2023-09-23T06:09:48.646385Z 0 [Note] Shutting down plugin 'INNODB_LOCKS'
2023-09-23T06:09:48.646386Z 0 [Note] Shutting down plugin 'INNODB_TRX'
2023-09-23T06:09:48.646388Z 0 [Note] Shutting down plugin 'XTRADB_ZIP_DICT_COLS'
2023-09-23T06:09:48.646389Z 0 [Note] Shutting down plugin 'XTRADB_ZIP_DICT'
2023-09-23T06:09:48.646391Z 0 [Note] Shutting down plugin 'XTRADB_RSEG'
2023-09-23T06:09:48.646392Z 0 [Note] Shutting down plugin 'XTRADB_INTERNAL_HASH_TABLES'
2023-09-23T06:09:48.646394Z 0 [Note] Shutting down plugin 'XTRADB_READ_VIEW'
2023-09-23T06:09:48.646395Z 0 [Note] Shutting down plugin 'InnoDB'
2023-09-23T06:09:48.646510Z 0 [Note] InnoDB: FTS optimize thread exiting.
2023-09-23T06:09:48.646758Z 0 [Note] InnoDB: Starting shutdown...
2023-09-23T06:09:48.759377Z 0 [Note] InnoDB: Dumping buffer pool(s) to /mysql/data/ib_buffer_pool
2023-09-23T06:09:48.760952Z 0 [Note] InnoDB: Buffer pool(s) dump completed at 230923 14:09:48
2023-09-23T06:09:49.534539Z 0 [Note] InnoDB: Waiting for page_cleaner to finish flushing of buffer pool
2023-09-23T06:09:50.752105Z 0 [Note] InnoDB: Shutdown completed; log sequence number 701945512
2023-09-23T06:09:50.753420Z 0 [Note] InnoDB: Removed temporary tablespace data file: "ibtmp1"
2023-09-23T06:09:50.753430Z 0 [Note] Shutting down plugin 'MyISAM'
2023-09-23T06:09:50.753493Z 0 [Note] Shutting down plugin 'MRG_MYISAM'
2023-09-23T06:09:50.753500Z 0 [Note] Shutting down plugin 'CSV'
2023-09-23T06:09:50.753503Z 0 [Note] Shutting down plugin 'MEMORY'
2023-09-23T06:09:50.753521Z 0 [Note] Shutting down plugin 'PERFORMANCE_SCHEMA'
2023-09-23T06:09:50.753564Z 0 [Note] Shutting down plugin 'sha256_password'
2023-09-23T06:09:50.753566Z 0 [Note] Shutting down plugin 'mysql_native_password'
2023-09-23T06:09:50.753716Z 0 [Note] Shutting down plugin 'binlog'
2023-09-23T06:09:50.754993Z 0 [Note] /usr/local/mysql/bin/mysqld: Shutdown complete

2、原因分析
提示不能设置socket lock文件，导致实例启动失败.在/mysql/data目录下发现实例没有启动的情况下存在mysql.sock.lock文件，导致在启动数据库实例时不能创建该文件.
[mysql@mysql-leo-slave data]$ ls -ltr mysql.sock.lock
-rw-------. 1 mysql mysql        5 Sep 22 23:14 mysql.sock.lock

3、解决方案
[mysql@mysql-leo-slave data]$ mv mysql.sock.lock mysql.sock.lock.bak
[mysql@mysql-leo-slave data]$ /usr/local/mysql/bin/mysqld_safe --defaults-file=/home/mysql/etc/my.cnf &
[1] 3604
[mysql@mysql-leo-slave data]$  mysqld_safe Adding '/usr/local/Percona-Server-5.7.21-20-Linux.x86_64.ssl101/lib/mysql/libjemalloc.so.1' to LD_PRELOAD for mysqld
2023-09-23T06:24:59.631636Z mysqld_safe Logging to '/mysql/data/mysql_error.log'.
2023-09-23T06:24:59.667097Z mysqld_safe Starting mysqld daemon with databases from /mysql/data
[mysql@mysql-leo-slave data]$ ps -ef|grep mysql
avahi       830      1  0 14:06 ?        00:00:00 avahi-daemon: running [mysql-leo-slave.local]
root       2837   2798  0 14:09 pts/0    00:00:00 su - mysql
mysql      2838   2837  0 14:09 pts/0    00:00:00 -bash
root       3555   3517  0 14:24 pts/1    00:00:00 su - mysql
mysql      3556   3555  0 14:24 pts/1    00:00:00 -bash
mysql      3594   3556  0 14:24 pts/1    00:00:00 tail -5000f mysql_error.log
mysql      3604   2838  0 14:24 pts/0    00:00:00 /bin/sh /usr/local/mysql/bin/mysqld_safe --defaults-file=/home/mysql/etc/my.cnf
mysql      4028   3604 20 14:24 pts/0    00:00:03 /usr/local/mysql/bin/mysqld --defaults-file=/home/mysql/etc/my.cnf --basedir=/usr/local/mysql --datadir=/mysql/data --plugin-dir=/usr/local/mysql/lib/mysql/plugin --log-error=/mysql/data/mysql_error.log --pid-file=/mysql/data/mysql.pid --socket=/mysql/data/mysql.sock --port=3306
mysql      4069   2838  0 14:25 pts/0    00:00:00 ps -ef
mysql      4070   2838  0 14:25 pts/0    00:00:00 grep --color=auto mysql

说明：如上所示，重命令mysql.sock.lock文件后，成功开启数据库.

参考文档：https://www.cnblogs.com/bianxj/articles/10796576.html