Bug in 4.0.17 mysqld_safe - deletes /var/lib/mysql/mysql.sock

We recently discovered a bug in the mysqld_safe script in MySQL's
MySQL-server-4.0.17-0 RPM. This is similar to the previously
reported 'Socket problem in mysqld_safe for 4.0.16'.

We run a master and slave on the same server. The master uses the
default socket /var/lib/mysql/mysql.sock. The slave uses
/var/lib/mysql/msyql-slave.sock.

Our config files contain [mysqld_safe] sections which specify
the correct socket, as do the [mysqld] sections. 

If we start the master, then start the slave, the master's socket
file always gets deleted. At first I thought we just needed to
add a 'socket = ...' stanza in [mysqld_safe], but this did not
fix the problem.

Turns out the problem lies in mysqld_safe. Very early on in this
script we see the following line:

safe_mysql_unix_port=${mysql_unix_port:-${MYSQL_UNIX_PORT:-/var/lib/mysql/mysql.sock}}

This apparently sets $safe_mysql_unix_port to '/var/lib/mysql/mysql.sock'.
After setting this variable, mysqld_safe then parses any specified config
file, and then any command-line arguments. At no point is $safe_mysql_unix_port
updated with config-file or command-line settings.

Later, we see the following extra bit of safety:
  rm -f $safe_mysql_unix_port $pid_file	# Some extra safety

Because $safe_mysql_unix_port is still set to /var/lib/mysql/mysql.sock,
the wrong socket gets deleted.

Our interim fix was to move the assignment of safe_mysql_unix_port to
later in the script; it's now happening after the config-file and command-line
args have been parsed.


 ------------------------------------------ 
 Donald Murray, P.Eng.
 Senior Software Engineer
 Pason Systems Corp.
 Direct: (403) 301-3473


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