Bug #71194 mysqld daemon should check if any process uses the socket file before removing

• Submitted: 20 Dec 2013 20:33
• Modified: 20 Dec 2013 22:39
• Reporter: Honza Horak (OCA)
• Status: Verified
• Category: MySQL Server: Options
• Severity: S3 (Non-critical)
• Version: 5.5.35, 5.6.16
• OS: Linux
• CPU Architecture: Any

[20 Dec 2013 20:33] Honza Horak

Description:
When running some MySQL daemon A and we are trying to run another instance B, while these conditions are met:
* network ports are different for A and B
* unix socket location is the same for A and B

Then the new daemon B removes the unix socket file that is actually necessary for daemon A.

How to repeat:
Steps to reproduce:
$ /usr/libexec/mysqld --port 13306 --datadir /var/lib/mysql/
$ fuser /var/lib/mysql/mysql.sock
$ /usr/libexec/mysqld --port 13307 --datadir /var/lib/mysql2/
$ fuser /var/lib/mysql/mysql.sock

Actual results:
/var/lib/mysql/mysql.sock:  5683
/var/lib/mysql/mysql.sock:  5717
which means the first daemon is not able to accept connections on the unix socket

Expected results:
/var/lib/mysql/mysql.sock:  5683
/var/lib/mysql/mysql.sock:  5683
the second daemon shouldn't start at all

Suggested fix:
Either check if some proc is attached to the socket or (portable solution) having a lock file for the socket file, that would contain pid of the process using the socket file.

[20 Dec 2013 20:36] Honza Horak

Socket file is also removed in the mysqld_safe script. This is wrong imho, so I'd propose to remove this removal in mysqld_safe and let it only for mysqld binary.

[20 Dec 2013 22:39] Sveta Smirnova

Thank you for the report.

Verified as described.