同事反馈说某个测试的MySQL数据库误删除了ibdata1文件，导致库启动不了，而且没做备份，能不能恢复？
如果误删除文件，但是数据库没进行过重启，只要删除的文件句柄还在系统中，就可以进行恢复，可以参考《Linux恢复误删文件的操作》。但是这套环境中，数据库进程已经被删除了，lsof未找到误删除的文件。
而且服务器无任何的备份，所以这条路关闭。
经过确认，可以不要这些数据了，能启动就行。
如果不管ibdata1，直接启动数据库，会提示如下错误，
代码语言：javascript复制2023-11-01T05:16:55.058805Z mysqld_safe Logging to '/mysql/3306/log/mysql-error.log'.
2023-11-01T05:16:55.082918Z mysqld_safe Starting mysqld daemon with databases from /mysql/3306/data
2023-11-01T05:16:55.088486Z 0 [Warning] Changed limits: max_open_files: 1024 (requested 5000)
2023-11-01T05:16:55.088539Z 0 [Warning] Changed limits: table_open_cache: 431 (requested 2000)
2023-11-01T13:16:55.237280 08:00 0 [Note] --secure-file-priv is set to NULL. Operations related to importing and exporting data are disabled
2023-11-01T13:16:55.237309 08:00 0 [Note] /usr/local/mysql7/bin/mysqld (mysqld 5.7.32-log) starting as process 46374 ...
2023-11-01T13:16:55.250775 08:00 0 [Note] InnoDB: PUNCH HOLE support available
2023-11-01T13:16:55.250793 08:00 0 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2023-11-01T13:16:55.250798 08:00 0 [Note] InnoDB: Uses event mutexes
2023-11-01T13:16:55.250801 08:00 0 [Note] InnoDB: GCC builtin __atomic_thread_fence() is used for memory barrier
2023-11-01T13:16:55.250804 08:00 0 [Note] InnoDB: Compressed tables use zlib 1.2.11
2023-11-01T13:16:55.250807 08:00 0 [Note] InnoDB: Using Linux native AIO
2023-11-01T13:16:55.250975 08:00 0 [Note] InnoDB: Number of pools: 1
2023-11-01T13:16:55.251057 08:00 0 [Note] InnoDB: Using CPU crc32 instructions
2023-11-01T13:16:55.252307 08:00 0 [Note] InnoDB: Initializing buffer pool, total size = 128M, instances = 1, chunk size = 128M
2023-11-01T13:16:55.258902 08:00 0 [Note] InnoDB: Completed initialization of buffer pool
2023-11-01T13:16:55.262430 08:00 0 [Note] InnoDB: If the mysqld execution user is authorized, page cleaner thread priority can be changed. See the man page of setpriority().
2023-11-01T13:16:55.276886 08:00 0 [ERROR] InnoDB: The Auto-extending innodb_system data file './ibdata1' is of a different size 0 pages (rounded down to MB) than specified in the .cnf file: initial 768 pages, max 0 (relevant if non-zero) pages!
2023-11-01T13:16:55.276904 08:00 0 [ERROR] InnoDB: Plugin initialization aborted with error Generic error
2023-11-01T13:16:55.888909 08:00 0 [ERROR] Plugin 'InnoDB' init function returned error.
2023-11-01T13:16:55.888944 08:00 0 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
2023-11-01T13:16:55.888949 08:00 0 [ERROR] Failed to initialize builtin plugins.
2023-11-01T13:16:55.888952 08:00 0 [ERROR] Aborting
2023-11-01T13:16:55.888967 08:00 0 [Note] Binlog end
2023-11-01T13:16:55.889025 08:00 0 [Note] Shutting down plugin 'CSV'
2023-11-01T13:16:55.889192 08:00 0 [Note] /usr/local/mysql7/bin/mysqld: Shutdown completeMySQL 5.7，如果同时删除ib_logfile0、ib_logfile1，启动数据库，是可以自动创建这三个文件的，
代码语言：javascript复制2023-11-01T09:13:52.873672Z 0 [Warning] Changed limits: max_open_files: 1024 (requested 5000)
2023-11-01T09:13:52.873731Z 0 [Warning] Changed limits: table_open_cache: 431 (requested 2000)
2023-11-01T17:13:53.011913 08:00 0 [Note] --secure-file-priv is set to NULL. Operations related to importing and exporting data are disabled
2023-11-01T17:13:53.011946 08:00 0 [Note] /usr/local/mysql7/bin/mysqld (mysqld 5.7.32-log) starting as process 95232 ...
2023-11-01T17:13:53.014739 08:00 0 [Note] InnoDB: PUNCH HOLE support available
2023-11-01T17:13:53.014758 08:00 0 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2023-11-01T17:13:53.014762 08:00 0 [Note] InnoDB: Uses event mutexes
2023-11-01T17:13:53.014766 08:00 0 [Note] InnoDB: GCC builtin __atomic_thread_fence() is used for memory barrier
2023-11-01T17:13:53.014768 08:00 0 [Note] InnoDB: Compressed tables use zlib 1.2.11
2023-11-01T17:13:53.014771 08:00 0 [Note] InnoDB: Using Linux native AIO
2023-11-01T17:13:53.014911 08:00 0 [Note] InnoDB: Number of pools: 1
2023-11-01T17:13:53.015005 08:00 0 [Note] InnoDB: Using CPU crc32 instructions
2023-11-01T17:13:53.015890 08:00 0 [Note] InnoDB: Initializing buffer pool, total size = 128M, instances = 1, chunk size = 128M
2023-11-01T17:13:53.020309 08:00 0 [Note] InnoDB: Completed initialization of buffer pool
2023-11-01T17:13:53.021508 08:00 0 [Note] InnoDB: If the mysqld execution user is authorized, page cleaner thread priority can be changed. See the man page of setpriority().
2023-11-01T17:13:53.032014 08:00 0 [Note] InnoDB: The first innodb_system data file 'ibdata1' did not exist. A new tablespace will be created!
2023-11-01T17:13:53.032158 08:00 0 [Note] InnoDB: Setting file './ibdata1' size to 12 MB. Physically writing the file full; Please wait ...
2023-11-01T17:13:53.107490 08:00 0 [Note] InnoDB: File './ibdata1' size is now 12 MB.
2023-11-01T17:13:53.107760 08:00 0 [Note] InnoDB: Setting log file ./ib_logfile101 size to 48 MB
2023-11-01T17:13:53.480921 08:00 0 [Note] InnoDB: Setting log file ./ib_logfile1 size to 48 MB
2023-11-01T17:13:54.438187 08:00 0 [Note] InnoDB: Renaming log file ./ib_logfile101 to ./ib_logfile0
2023-11-01T17:13:54.438251 08:00 0 [Warning] InnoDB: New log files created, LSN=45790
2023-11-01T17:13:54.438264 08:00 0 [Note] InnoDB: Creating shared tablespace for temporary tables
2023-11-01T17:13:54.438329 08:00 0 [Note] InnoDB: Setting file './ibtmp1' size to 12 MB. Physically writing the file full; Please wait ...
2023-11-01T17:13:54.505869 08:00 0 [Note] InnoDB: File './ibtmp1' size is now 12 MB.
2023-11-01T17:13:54.506059 08:00 0 [Note] InnoDB: Doublewrite buffer not found: creating new
2023-11-01T17:13:54.527522 08:00 0 [Note] InnoDB: Doublewrite buffer created
2023-11-01T17:13:54.531060 08:00 0 [Note] InnoDB: 96 redo rollback segment(s) found. 96 redo rollback segment(s) are active.
2023-11-01T17:13:54.531078 08:00 0 [Note] InnoDB: 32 non-redo rollback segment(s) are active.
2023-11-01T17:13:54.531169 08:00 0 [Warning] InnoDB: Creating foreign key constraint system tables.
2023-11-01T17:13:54.541415 08:00 0 [Note] InnoDB: Foreign key constraint system tables created
2023-11-01T17:13:54.541468 08:00 0 [Note] InnoDB: Creating tablespace and datafile system tables.
2023-11-01T17:13:54.542864 08:00 0 [Note] InnoDB: Tablespace and datafile system tables created.
2023-11-01T17:13:54.542889 08:00 0 [Note] InnoDB: Creating sys_virtual system tables.
2023-11-01T17:13:54.544077 08:00 0 [Note] InnoDB: sys_virtual table created
2023-11-01T17:13:54.544168 08:00 0 [Note] InnoDB: Waiting for purge to start
2023-11-01T17:13:54.594720 08:00 0 [Note] InnoDB: 5.7.32 started; log sequence number 0
2023-11-01T17:13:54.596887 08:00 0 [Warning] InnoDB: Cannot open table mysql/plugin from the internal data dictionary of InnoDB though the .frm file for the table exists. Please refer to http://dev.mysql.com/doc/refman/5.7/en/innodb-troubleshooting.html for how to resolve the issue.
mysqld: Table 'mysql.plugin' doesn't exist
2023-11-01T17:13:54.596922 08:00 0 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it.
2023-11-01T17:13:54.600988 08:00 0 [Warning] InnoDB: Cannot open table mysql/gtid_executed from the internal data dictionary of InnoDB though the .frm file for the table exists. Please refer to http://dev.mysql.com/doc/refman/5.7/en/innodb-troubleshooting.html for how to resolve the issue.
mysqld: Table 'mysql.gtid_executed' doesn't exist
2023-11-01T17:13:54.601016 08:00 0 [Warning] Gtid table is not ready to be used. Table 'mysql.gtid_executed' cannot be opened.
2023-11-01T17:13:54.602556 08:00 0 [Note] Found ca.pem, server-cert.pem and server-key.pem in data directory. Trying to enable SSL support using them.
2023-11-01T17:13:54.602568 08:00 0 [Note] Skipping generation of SSL certificates as certificate files are present in data directory.
2023-11-01T17:13:54.603431 08:00 0 [Warning] CA certificate ca.pem is self signed.
2023-11-01T17:13:54.603465 08:00 0 [Note] Skipping generation of RSA key pair as key files are present in data directory.
2023-11-01T17:13:54.603546 08:00 0 [Note] Server hostname (bind-address): '*'; port: 3306
2023-11-01T17:13:54.603630 08:00 0 [Note] IPv6 is available.
2023-11-01T17:13:54.603640 08:00 0 [Note] - '::' resolves to '::';
2023-11-01T17:13:54.603677 08:00 0 [Note] Server socket created on IP: '::'.
2023-11-01T17:13:54.604700 08:00 0 [Warning] Insecure configuration for --pid-file: Location '/mysql' in the path is accessible to all OS users. Consider choosing a different directory.
2023-11-01T17:13:54.604900 08:00 0 [Warning] InnoDB: Cannot open table mysql/server_cost from the internal data dictionary of InnoDB though the .frm file for the table exists. Please refer to http://dev.mysql.com/doc/refman/5.7/en/innodb-troubleshooting.html for how to resolve the issue.
2023-11-01T17:13:54.604919 08:00 0 [Warning] Failed to open optimizer cost constant tables
2023-11-01T17:13:54.605366 08:00 0 [Warning] InnoDB: Cannot open table mysql/time_zone_leap_second from the internal data dictionary of InnoDB though the .frm file for the table exists. Please refer to http://dev.mysql.com/doc/refman/5.7/en/innodb-troubleshooting.html for how to resolve the issue.
2023-11-01T17:13:54.605380 08:00 0 [Warning] Can't open and lock time zone table: Table 'mysql.time_zone_leap_second' doesn't exist trying to live without them
2023-11-01T17:13:54.605806 08:00 0 [Warning] InnoDB: Cannot open table mysql/servers from the internal data dictionary of InnoDB though the .frm file for the table exists. Please refer to http://dev.mysql.com/doc/refman/5.7/en/innodb-troubleshooting.html for how to resolve the issue.
2023-11-01T17:13:54.605824 08:00 0 [ERROR] Can't open and lock privilege tables: Table 'mysql.servers' doesn't exist
2023-11-01T17:13:54.605991 08:00 0 [Warning] InnoDB: Cannot open table mysql/slave_master_info from the internal data dictionary of InnoDB though the .frm file for the table exists. Please refer to http://dev.mysql.com/doc/refman/5.7/en/innodb-troubleshooting.html for how to resolve the issue.
2023-11-01T17:13:54.606061 08:00 0 [Warning] InnoDB: Cannot open table mysql/slave_relay_log_info from the internal data dictionary of InnoDB though the .frm file for the table exists. Please refer to http://dev.mysql.com/doc/refman/5.7/en/innodb-troubleshooting.html for how to resolve the issue.
2023-11-01T17:13:54.606113 08:00 0 [Warning] InnoDB: Cannot open table mysql/slave_master_info from the internal data dictionary of InnoDB though the .frm file for the table exists. Please refer to http://dev.mysql.com/doc/refman/5.7/en/innodb-troubleshooting.html for how to resolve the issue.
2023-11-01T17:13:54.606122 08:00 0 [Warning] Info table is not ready to be used. Table 'mysql.slave_master_info' cannot be opened.
2023-11-01T17:13:54.606181 08:00 0 [Warning] InnoDB: Cannot open table mysql/slave_worker_info from the internal data dictionary of InnoDB though the .frm file for the table exists. Please refer to http://dev.mysql.com/doc/refman/5.7/en/innodb-troubleshooting.html for how to resolve the issue.
2023-11-01T17:13:54.606230 08:00 0 [Warning] InnoDB: Cannot open table mysql/slave_relay_log_info from the internal data dictionary of InnoDB though the .frm file for the table exists. Please refer to http://dev.mysql.com/doc/refman/5.7/en/innodb-troubleshooting.html for how to resolve the issue.
2023-11-01T17:13:54.606242 08:00 0 [Warning] Info table is not ready to be used. Table 'mysql.slave_relay_log_info' cannot be opened.
2023-11-01T17:13:54.606263 08:00 0 [Note] Failed to start slave threads for channel ''
2023-11-01T17:13:54.609674 08:00 0 [Note] Event Scheduler: Loaded 0 events
2023-11-01T17:13:54.618992 08:00 0 [Note] /usr/local/mysql7/bin/mysqld: ready for connections.
Version: '5.7.32-log' socket: '/mysql/3306/tmp/mysql.sock' port: 3306 MySQL Community Server (GPL)因此针对MySQL 5.7，如果误删除ibdata1，不需要数据的前提下，可以再删除ib_logfile0、ib_logfile1，让MySQL可以自动创建这几个文件，带起数据库。
但同事用的MariaDB，删除这些文件，执行数据库启动的指令，虽然能自动创建这几个文件，但无法启动，提示如下错误，
代码语言：javascript复制systemctl status mariadb.service
● mariadb.service - MariaDB database server
Loaded: loaded (/usr/lib/systemd/system/mariadb.service; disabled; vendor preset: disabled)
Active: failed (Result: exit-code) since 三 2023-11-01 13:30:55 CST; 12s ago
Process: 10099 ExecStartPost=/usr/libexec/mariadb-wait-ready $MAINPID (code=exited, status=1/FAILURE)
Process: 10098 ExecStart=/usr/bin/mysqld_safe --basedir=/usr (code=exited, status=0/SUCCESS)
Process: 10067 ExecStartPre=/usr/libexec/mariadb-prepare-db-dir %n (code=exited, status=0/SUCCESS)
Main PID: 10098 (code=exited, status=0/SUCCESS)
11月 01 13:30:49 localhost.localdomain systemd[1]: Starting MariaDB database server...
11月 01 13:30:49 localhost.localdomain mariadb-prepare-db-dir[10067]: Database MariaDB is probably initialized in /var/lib/mysql already, nothing is done.
11月 01 13:30:49 localhost.localdomain mariadb-prepare-db-dir[10067]: If this is not the case, make sure the /var/lib/mysql is empty before running ...b-dir.
11月 01 13:30:49 localhost.localdomain mysqld_safe[10098]: 231101 13:30:49 mysqld_safe Logging to '/var/log/mariadb/mariadb.log'.
11月 01 13:30:49 localhost.localdomain mysqld_safe[10098]: 231101 13:30:49 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
11月 01 13:30:55 localhost.localdomain systemd[1]: mariadb.service: control process exited, code=exited status=1
11月 01 13:30:55 localhost.localdomain systemd[1]: Failed to start MariaDB database server.
11月 01 13:30:55 localhost.localdomain systemd[1]: Unit mariadb.service entered failed state.
11月 01 13:30:55 localhost.localdomain systemd[1]: mariadb.service failed.
Hint: Some lines were ellipsized, use -l to show in full.登录数据库，说的是找不到sock，实际有这个文件，
代码语言：javascript复制[root@localhost ~]# mysql -u root -p
Enter password:
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (111)我觉得应该比较接近答案了，但是受限于进度，还是重装了。
从这个引申出最重要的，无论什么库，建议还是做备份，无备份的库，就像是裸奔，存在各种风险。
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