Troubleshooting MySQL 5.7 on Arch Linux

TLDR

Change ownership of directory "/var/lib/mysql" to the respective owner:group, mysql:mysql in my case, if MySQL does not start and something like the below pops up in logs
```
[Warning] Can't create file /var/lib/mysql/user.lower-test
[ERROR] failed to set datadir to /var/lib/mysql
```

Leverage option skip-grant-tables (with caution, if your machine is connected to the outside world) with MySQL to reset password, if you can not log into MySQL

$ echo "skip-grant-tables" | sudo tee -a /etc/mysql/my.cnf
$ sudo systemctl restart mysqld.service
$ mysql

# wanted a no-password login for root user here
mysql> UPDATE mysql.user SET authentication_string = null WHERE User = 'root';

$ sudo sed -i '/skip-grant-tables/d' /etc/mysql/my.cnf
$ sudo systemctl restart mysqld.service

Context

MySQL is installed from package "mysql57" via yay.

Troubleshooting

MySQL Does not Start

Good ol' ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2) printed on screen when trying to use MySQL CLI with $ sudo mysql
It showed up dead with exit status 1 in $ systemctl status mysqld.service

Found the below in logs with $ journalctl -u mysqld.service

[Warning] Can't create file /var/lib/mysql/user.lower-test
[ERROR] failed to set datadir to /var/lib/mysql

Realized that it could be something about insufficient permission, with some googling

It said the owner:group is root:root in $ ls -al /var/lib | grep mysql
Check the service file (mine was at "/usr/lib/systemd/system/mysqld.service", shown right after "Loaded: loaded" in $ systemctl status mysqld.service) to see how MySQL was being started
Turned out that it was trying to use mysql:mysql as the user:group to start the service

$ sudo chown mysql:mysql
Showed up running after restarting MySQL with $ sudo systemctl restart mysqld.service

MySQL Does not Start

Failed to log in with root user, $ sudo mysql
Appended the option skip-grant-tables to "/etc/mysql/my.cnf" then restart MySQL

Exercise this with caution. You might want to append skip-networking to the config file as well to cut remote connections
```
# may use "skip-grant-tables\nskip-networking" instead to play safe here
$ echo "skip-grant-tables" | sudo tee -a /etc/mysql/my.cnf
$ sudo systemctl restart mysqld.service
```

Logged into MySQL to remove password

mysql> UPDATE mysql.user SET authentication_string = null WHERE User = 'root';

Turned of the option(s) then restart MySQL again

# or use regex '/^skip-grant-tables$\|%skip-networking$/d'
$ sudo sed -i '/^skip-grant-tables$/d' /etc/mysql/my.cnf
$ sudo systemctl restart mysqld.service

$ sudo mysql to log in