I find strange bug or error but I not sure if systemD or mysql.
I have two instance in same server db00, If I stop or restart any instance, it delete the pid and socket file of the other service but the other service is still working.
Server version: 8.0.23-14 Percona Server
[mysqld@db01]
pid-file = /var/run/mysqld/mysql_db01.pid
socket = /var/run/mysqld/mysql_db01.sock
datadir = /var/lib/mysql_db01
log-error = /var/log/mysql_db01/error.log
port = 3306
server_id = 101
mysqlx = 0
...
[mysqld@db02]
pid-file = /var/run/mysqld/mysql_db02.pid
socket = /var/run/mysqld/mysql_db02.sock
datadir = /var/lib/mysql_db02
log-error = /var/log/mysql_db02/error.log
port = 3307
server_id = 202
mysqlx = 0
...
for example:
both services are running , and the files exist in /var/run/mysqld/
#ls -l /var/run/mysqld/:
drwxr-xr-x 2 root root 40 May 27 01:15 ./
drwxr-xr-x 35 root root 1080 May 27 01:15 ../
-rw-r----- 1 mysql mysql 7 May 27 01:07 mysql_db01.pid
srwxrwxrwx 1 mysql mysql 0 May 27 01:07 mysql_db01.sock=
-rw------- 1 mysql mysql 7 May 27 01:07 mysql_db01.sock.lock
-rw-r----- 1 mysql mysql 7 May 27 01:08 mysql_db02.pid
srwxrwxrwx 1 mysql mysql 0 May 27 01:08 mysql_db02.sock=
-rw------- 1 mysql mysql 7 May 27 01:08 mysql_db02.sock.lock
#
stop the service ,mysql@db02 and delete all files in /var/run/mysql
#systemctl stop mysql@db02
#ll /var/run/mysqld/:
drwxr-xr-x 2 root root 40 May 27 01:15 ./
drwxr-xr-x 35 root root 1080 May 27 01:15 ../
#
For restore the files we need stop (or restart) the other instance
#systemctl stop mysql@db01
#ll /var/run/mysqld/:
drwxr-xr-x 2 root root 40 May 27 01:15 ./
drwxr-xr-x 35 root root 1080 May 27 01:15 ../
#
And start one by one.
#systemctl start mysql@db01
#ll /var/run/mysqld/
drwxr-xr-x 2 root root 40 May 27 01:15 ./
drwxr-xr-x 35 root root 1080 May 27 01:15 ../
-rw-r----- 1 mysql mysql 7 May 27 01:18 mysql_db01.pid
srwxrwxrwx 1 mysql mysql 0 May 27 01:18 mysql_db01.sock
-rw------- 1 mysql mysql 7 May 27 01:18 mysql_db01.sock.lock
#
#systemctl start mysql@db02
#ll /var/run/mysqld/
drwxr-xr-x 2 root root 40 May 27 01:15 ./
drwxr-xr-x 35 root root 1080 May 27 01:15 ../
-rw-r----- 1 mysql mysql 7 May 27 01:18 mysql_db01.pid
srwxrwxrwx 1 mysql mysql 0 May 27 01:18 mysql_db01.sock
-rw------- 1 mysql mysql 7 May 27 01:18 mysql_db01.sock.lock
-rw-r----- 1 mysql mysql 7 May 27 01:19 mysql_db02.pid
srwxrwxrwx 1 mysql mysql 0 May 27 01:19 mysql_db02.sock
-rw------- 1 mysql mysql 7 May 27 01:19 mysql_db02.sock.lock
I don’t think it is good idea create other dir in /var/run (in case of reboot), any idea? maybe is service or config mysql