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Isaac Sutherland
Asked: 2017-12-15 13:00:32 +0800 CST

Systemd boot ordering: Wait for mysql.sock

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I have an openvpn tunnel which runs an --up script which queries a local mysql database for IP routing information and then applies the routes. However, since both the openvpn and mysql systemd services are configured with the After=network.target directive, I have a race condition: /var/run/mysqld/mysqld.sock might exist when the --up script runs, or it might not. If the sock file doesn't exist, then my script dies and the system doesn't initialize properly.

I thought that changing my openvpn.service directive to After=network.target mysql.service and running systemctl daemon-reload would do the trick. However, I added ls -lh /var/run/mysqld/mysqld.sock to the beginning of my --up script, and it still sometimes reports ls: cannot access '/var/run/mysqld/mysqld.sock': No such file or directory.

My guess is that systemd's is not using the sock file to determine whether or not mysqld has finished loading but rather some criteria that happens before the sock file is created.

Is there a way to tell systemd to not recognize mysql.service as having started until the sock file has been created?

mysql

2 Answers

  1. i had the same problem, start some other service after mysql started

    First i disable my service

    systemctl disable rfid-server

    After that i modified my rfid-server.service file

    [Unit]
Description=rfid server
After=mysql.service

[Service]
ExecStart=/opt/rfid-server-service/deploy/start.sh

[Install]
WantedBy=multi-user.target mysql.service

    An the i re-enable my service

    systemctl enable /complete/path/to/service

Created symlink from /etc/systemd/system/multi-user.target.wants/rfid-server.service to /opt/rfid-server-service/rfid-server.service.
Created symlink from /etc/systemd/system/mysql.service.wants/rfid-server.service to /opt/rfid-server-service/rfid-server.service.
Created symlink from /etc/systemd/system/rfid-server.service to /opt/rfid-server-service/rfid-server.service.

    As you can see, it create the symlink to mysql.service.wants

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  2. May be you should add ConditionPathExists check in your service file?

    There is quote from systemd documentation:

    With ConditionPathExists= a file existence condition is checked before a unit is started. If the specified absolute path name does not exist, the condition will fail. If the absolute path name passed to ConditionPathExists= is prefixed with an exclamation mark ("!"), the test is negated, and the unit is only started if the path does not exist.

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