# 文件上传位置在/opt/mysql/下面
cd /opt/mysql/

# 解压安装包
[root@zkmet mysql]# xz -d mysql-8.0.27-linux-glibc2.12-x86_64.tar.xz 
[root@zkmet mysql]# tar -xvf mysql-8.0.27-linux-glibc2.12-x86_64.tar 

# 文件夹重命名为mysql8 
mv mysql-8.0.27-linux-glibc2.12-x86_64 mysql8

# 安装包移动（复制）至原安装包目录下,我的是/var/lib/ 
cp mysql8 /var/lib/

# 更改文件夹所属
chown -R mysql.mysql /var/lib/mysql8/

#for8.0
sql_mode = STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION
character-set-server = utf8
collation_server = utf8_general_ci
basedir = /var/lib/mysql8
skip_ssl
default_authentication_plugin=mysql_native_password

# 进入原5.7 mysql命令行 正确关闭数据库
[root@zkmet mysql]# mysql -uroot -p
Enter password: 

mysql> select version();
+------------+
| version()  |
+------------+
| 5.7.23-log |
+------------+
1 row in set (0.00 sec)

mysql> show variables like 'innodb_fast_shutdown';
+----------------------+-------+
| Variable_name        | Value |
+----------------------+-------+
| innodb_fast_shutdown | 1     |
+----------------------+-------+
1 row in set (0.00 sec)
# 确保数据都刷到硬盘上，更改成0
mysql> set global innodb_fast_shutdown=0;
Query OK, 0 rows affected (0.00 sec)

mysql> shutdown;
Query OK, 0 rows affected (0.00 sec)

mysql> exit
Bye

# 执行命令/var/lib/mysql8/bin/mysqld_safe --defaults-file=/etc/my.cnf --user=mysql &
[root@zkmet mysql]# /var/lib/mysql8/bin/mysqld_safe --defaults-file=/etc/my.cnf --user=mysql &

# 我的一直卡在这个页面，还以为出错了，可以另起一个客户端，登录到数据库select version();查看数据库版本是否更新成功。
[1] 1787
[root@zkmet mysql]# 2021-11-12T06:32:56.314320Z mysqld_safe Logging to '/var/log/mysqld.log'.
2021-11-12T06:32:56.337533Z mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql
2021-11-12T07:26:29.183302Z mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended

[root@zkmet etc]# mysql -uroot -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or g.
Your MySQL connection id is 14
Server version: 8.0.27 MySQL Community Server - GPL

Copyright (c) 2000, 2021, Oracle and/or its affiliates.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or 'h' for help. Type 'c' to clear the current input statement.

mysql> select version();
+-----------+
| version() |
+-----------+
| 8.0.27    |
+-----------+
1 row in set (0.01 sec)

# 修改PATH变量
[root@zkmet etc]# vi /etc/profile 
# 将PATH中的/usr/local/mysql/bin改为/usr/local/mysql8/bin 

# 生效验证
[root@zkmet etc]# source /etc/profile
[root@zkmet etc]# which mysql
/var/lib/mysql8/bin/mysql
[root@zkmet etc]# mysql -V
[root@zkmet etc]# mysql -V
mysql  Ver 8.0.27 for Linux on x86_64 (MySQL Community Server - GPL)

[root@zkmet ~]# mysql -uroot -p
Enter password: 
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)

[root@zkmet etc]# find / -name mysql.sock
/var/lib/mysql/mysql.sock

[mysqld]
socket = /var/lib/mysql/mysql.sock

[client]
socket = /var/lib/mysql/mysql.sock

[root@zkmet bin]# service mysqld restart
停止 mysqld：                                              [确定]
MySQL Daemon failed to start.
正在启动 mysqld：                                          [失败]

07:47:22 UTC - mysqld got signal 6 ;
This could be because you hit a bug. It is also possible that this binary
or one of the libraries it was linked against is corrupt, improperly built,
or misconfigured. This error can also be caused by malfunctioning hardware.
Attempting to collect some information that could help diagnose the problem.
As this is a crash and something is definitely wrong, the information
collection process might fail.

key_buffer_size=8388608
read_buffer_size=131072
max_used_connections=0
max_threads=151
thread_count=0
connection_count=0
It is possible that mysqld could use up to 
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 68196 K  bytes of memory
Hope that's ok; if not, decrease some variables in the equation.

Thread pointer: 0x0
Attempting backtrace. You can use the following information to find out
where mysqld died. If you see no messages after this, something went
terribly wrong...
stack_bottom = 0 thread_stack 0x40000
/usr/sbin/mysqld(my_print_stacktrace+0x35)[0xf559e5]
/usr/sbin/mysqld(handle_fatal_signal+0x4a4)[0x7d4bd4]
/lib64/libpthread.so.0[0x3a2fe0f710]
/lib64/libc.so.6(gsignal+0x35)[0x3a2fa32925]
/lib64/libc.so.6(abort+0x175)[0x3a2fa34105]
/usr/sbin/mysqld(_Z18ut_print_timestampP8_IO_FILE+0x0)[0x7c3cf8]
/usr/sbin/mysqld(_ZN2ib5fatalD1Ev+0xb3)[0x11610d3]
/usr/sbin/mysqld[0x1203338]
/usr/sbin/mysqld[0x1203b98]
/usr/sbin/mysqld(_Z6fil_ioRK9IORequestbRK9page_id_tRK11page_size_tmmPvS8_+0x29e)[0x120c12e]
/usr/sbin/mysqld[0x11bf616]
/usr/sbin/mysqld(_Z13buf_read_pageRK9page_id_tRK11page_size_t+0x40)[0x11c0090]
/usr/sbin/mysqld(_Z16buf_page_get_genRK9page_id_tRK11page_size_tmP11buf_block_tmPKcmP5mtr_tb+0xd21)[0x11a1f01]
/usr/sbin/mysqld(_Z31trx_rseg_get_n_undo_tablespacesPm+0x15d)[0x114244d]
/usr/sbin/mysqld(_Z34innobase_start_or_create_for_mysqlv+0x2981)[0x11185c1]
/usr/sbin/mysqld[0x1000e8a]
/usr/sbin/mysqld(_Z24ha_initialize_handlertonP13st_plugin_int+0x51)[0x8219f1]
/usr/sbin/mysqld[0xd39d26]
/usr/sbin/mysqld(_Z40plugin_register_builtin_and_init_core_sePiPPc+0x3e4)[0xd3af44]
/usr/sbin/mysqld[0x7cb006]
/usr/sbin/mysqld(_Z11mysqld_mainiPPc+0x957)[0x7ce657]
/lib64/libc.so.6(__libc_start_main+0xfd)[0x3a2fa1ed1d]
/usr/sbin/mysqld[0x7c4ac9]
The manual page at http://dev.mysql.com/doc/mysql/en/crashing.html contains
information that should help you find out what is causing the crash.
2021-11-12T07:56:58.641391Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
2021-11-12T07:56:58.641442Z 0 [Warning] 'NO_AUTO_CREATE_USER' sql mode was not set.
2021-11-12T07:56:58.644936Z 0 [Note] /usr/sbin/mysqld (mysqld 5.7.25-log) starting as process 6345 ...
2021-11-12T07:56:58.644998Z 0 [ERROR] Can't find error-message file '/usr/share/mysql/errmsg.sys'. Check error-message file location and 'lc-messages-dir' configuration directive.
2021-11-12T07:56:58.651266Z 0 [Note] InnoDB: PUNCH HOLE support available
2021-11-12T07:56:58.651337Z 0 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2021-11-12T07:56:58.651344Z 0 [Note] InnoDB: Uses event mutexes
2021-11-12T07:56:58.651353Z 0 [Note] InnoDB: GCC builtin __sync_synchronize() is used for memory barrier
2021-11-12T07:56:58.651361Z 0 [Note] InnoDB: Compressed tables use zlib 1.2.11
2021-11-12T07:56:58.651370Z 0 [Note] InnoDB: Using Linux native AIO
2021-11-12T07:56:58.651667Z 0 [Note] InnoDB: Number of pools: 1
2021-11-12T07:56:58.651794Z 0 [Note] InnoDB: Using CPU crc32 instructions
2021-11-12T07:56:58.654249Z 0 [Note] InnoDB: Initializing buffer pool, total size = 128M, instances = 1, chunk size = 128M
2021-11-12T07:56:58.667767Z 0 [Note] InnoDB: Completed initialization of buffer pool
2021-11-12T07:56:58.671260Z 0 [Note] InnoDB: If the mysqld execution user is authorized, page cleaner thread priority can be changed. See the man page of setpriority().
2021-11-12T07:56:58.684155Z 0 [ERROR] [FATAL] InnoDB: Table flags are 0 in the data dictionary but the flags in file ./ibdata1 are 0x4000!
2021-11-12 15:56:58 0x7f73adfaf720  InnoDB: Assertion failure in thread 140134816872224 in file ut0ut.cc line 942
InnoDB: We intentionally generate a memory trap.
InnoDB: Submit a detailed bug report to http://bugs.mysql.com.
InnoDB: If you get repeated assertion failures or crashes, even
InnoDB: immediately after the mysqld startup, there may be
InnoDB: corruption in the InnoDB tablespace. Please refer to
InnoDB: http://dev.mysql.com/doc/refman/5.7/en/forcing-innodb-recovery.html
InnoDB: about forcing recovery.
07:56:58 UTC - mysqld got signal 6 ;
This could be because you hit a bug. It is also possible that this binary
or one of the libraries it was linked against is corrupt, improperly built,
or misconfigured. This error can also be caused by malfunctioning hardware.
Attempting to collect some information that could help diagnose the problem.
As this is a crash and something is definitely wrong, the information
collection process might fail.

key_buffer_size=8388608
read_buffer_size=131072
max_used_connections=0
max_threads=151
thread_count=0
connection_count=0
It is possible that mysqld could use up to 
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 68196 K  bytes of memory
Hope that's ok; if not, decrease some variables in the equation.

Thread pointer: 0x0
Attempting backtrace. You can use the following information to find out
where mysqld died. If you see no messages after this, something went
terribly wrong...
stack_bottom = 0 thread_stack 0x40000
/usr/sbin/mysqld(my_print_stacktrace+0x35)[0xf559e5]
/usr/sbin/mysqld(handle_fatal_signal+0x4a4)[0x7d4bd4]
/lib64/libpthread.so.0[0x3a2fe0f710]
/lib64/libc.so.6(gsignal+0x35)[0x3a2fa32925]
/lib64/libc.so.6(abort+0x175)[0x3a2fa34105]
/usr/sbin/mysqld(_Z18ut_print_timestampP8_IO_FILE+0x0)[0x7c3cf8]
/usr/sbin/mysqld(_ZN2ib5fatalD1Ev+0xb3)[0x11610d3]
/usr/sbin/mysqld[0x1203338]
/usr/sbin/mysqld[0x1203b98]
/usr/sbin/mysqld(_Z6fil_ioRK9IORequestbRK9page_id_tRK11page_size_tmmPvS8_+0x29e)[0x120c12e]
/usr/sbin/mysqld[0x11bf616]
/usr/sbin/mysqld(_Z13buf_read_pageRK9page_id_tRK11page_size_t+0x40)[0x11c0090]
/usr/sbin/mysqld(_Z16buf_page_get_genRK9page_id_tRK11page_size_tmP11buf_block_tmPKcmP5mtr_tb+0xd21)[0x11a1f01]
/usr/sbin/mysqld(_Z31trx_rseg_get_n_undo_tablespacesPm+0x15d)[0x114244d]
/usr/sbin/mysqld(_Z34innobase_start_or_create_for_mysqlv+0x2981)[0x11185c1]
/usr/sbin/mysqld[0x1000e8a]
/usr/sbin/mysqld(_Z24ha_initialize_handlertonP13st_plugin_int+0x51)[0x8219f1]
/usr/sbin/mysqld[0xd39d26]
/usr/sbin/mysqld(_Z40plugin_register_builtin_and_init_core_sePiPPc+0x3e4)[0xd3af44]
/usr/sbin/mysqld[0x7cb006]
/usr/sbin/mysqld(_Z11mysqld_mainiPPc+0x957)[0x7ce657]
/lib64/libc.so.6(__libc_start_main+0xfd)[0x3a2fa1ed1d]
/usr/sbin/mysqld[0x7c4ac9]
The manual page at http://dev.mysql.com/doc/mysql/en/crashing.html contains
information that should help you find out what is causing the crash.

# 都准备重装mysql的,后来死马当活马医，尝试执行下面的命令又好了
/var/lib/mysql8/bin/mysqld_safe --defaults-file=/etc/my.cnf --user=mysql &