MySQL Bugs: #73860: Unknown system variable 'symbolic

Bug #73860	Unknown system variable 'symbolic_links'
Submitted:	9 Sep 2014 13:32	Modified:	11 Sep 2014 14:34
Reporter:	Shahriyar Rzayev	Email Updates:
Status:	Not a Bug	Impact on me:	None
Category:	MySQL Server: Options	Severity:	S1 (Critical)
Version:	5.6.20	OS:	Linux (CentOS 6.5)
Assigned to:		CPU Architecture:	Any

Description:
After installing 5.6.20 MySQL from official YUM Repo in its default created my.cnf file there is an entry:

# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0

But in documentation there is no such entry about this variable:

http://dev.mysql.com/doc/refman/5.6/en/server-system-variables.html

Also it will raise an error when querying for this variable:

mysql> select @@symbolic_links;
ERROR 1193 (HY000): Unknown system variable 'symbolic_links'

Interesting thing that MySQL does not complain and starts as usual with this "non-existing" variable.

Very similar to:

http://bugs.mysql.com/bug.php?id=73833

How to repeat:
Just install latest 5.6.20 GA from YUM repo and open default fresh-created my.cnf file.
You will see:
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0

Query for it to see the error.

Suggested fix:
Maybe some information related to this variable if it is exists.
If it is not exists do not allow start MySQL with it or smth else.

There is a 'have_symlink' variable described here:
http://dev.mysql.com/doc/refman/5.5/en/symbolic-links.html
(and I checked it is available in all versions from 5.0x - even on Windows)

-- Peter
-- not a MySQL/Oracle person

Replaced:
  mysql.x86_64 0:5.1.73-3.el6_5   mysql-devel.x86_64 0:5.1.73-3.el6_5   mysql-libs.x86_64 0:5.1.73-3.el6_5   mysql-server.x86_64 0:5.1.73-3.el6_5

Complete!
[root@tikal miguel]# cat /etc/my.cnf
# For advice on how to change settings please see
# http://dev.mysql.com/doc/refman/5.6/en/server-configuration-defaults.html

[mysqld]
#
# Remove leading # and set to the amount of RAM for the most important data
# cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%.
# innodb_buffer_pool_size = 128M
#
# Remove leading # to turn on a very important data integrity option: logging
# changes to the binary log between backups.
# log_bin
#
# Remove leading # to set options mainly useful for reporting servers.
# The server defaults are faster for transactions and fast SELECTs.
# Adjust sizes as needed, experiment to find the optimal values.
# join_buffer_size = 128M
# sort_buffer_size = 2M
# read_rnd_buffer_size = 2M
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock

# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0

# Recommended in standard MySQL setup
sql_mode=NO_ENGINE_SUBSTITUTION,STRICT_TRANS_TABLES

[mysqld_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid

http://dev.mysql.com/doc/refman/5.6/en/server-options.html#option_mysqld_symbolic-links

"Command-Line Format	--symbolic-links
Option-File Format	symbolic-links

Enable or disable symbolic link support. This option has different effects on Windows and Unix:

    On Windows, enabling symbolic links enables you to establish a symbolic link to a database directory by creating a db_name.sym file that contains the path to the real directory. See Section 8.11.3.1.3, “Using Symbolic Links for Databases on Windows”.

    On Unix, enabling symbolic links means that you can link a MyISAM index file or data file to another directory with the INDEX DIRECTORY or DATA DIRECTORY options of the CREATE TABLE statement. If you delete or rename the table, the files that its symbolic links point to also are deleted or renamed. See Section 8.11.3.1.2, “Using Symbolic Links for MyISAM Tables on Unix”.

So in conclusion,
Even if we have this variable as:

Command-Line Format	--symbolic-links
Option-File Format	symbolic-links

We can not query for this variable's value?

mysql> select @@symbolic_links;
ERROR 1193 (HY000): Unknown system variable 'symbolic_links'

The error displayed is because isn't a variable instead is a server option you can see at:

http://dev.mysql.com/doc/refman/5.6/en/mysqld-option-tables.html

third column is empty, please check it,  you could find others server options with the same behavior if the third column is empty. Thanks.