mysqld_multi is designed to manage several mysqld processes that
listen for connections on different Unix socket files and TCP/IP
ports. It can start or stop servers, or report their current
status.
mysqld_multi searches for groups named [mysqldN] in my.cnf (or in
the file named by the --config-file option). N can be any
positive integer. This number is referred to in the following
discussion as the option group number, or GNR. Group numbers
distinguish option groups from one another and are used as
arguments to mysqld_multi to specify which servers you want to
start, stop, or obtain a status report for. Options listed in
these groups are the same that you would use in the [mysqld]
group used for starting mysqld. However, when using multiple
servers, it is necessary that each one use its own value for
options such as the Unix socket file and TCP/IP port number.
To invoke mysqld_multi, use the following syntax:
shell> mysqld_multi [options] {start|stop|report} [GNR[,GNR] ...]
start, stop, and report indicate which operation to perform. You
can perform the designated operation for a single server or
multiple servers, depending on the GNR list that follows the
option name. If there is no list, mysqld_multi performs the
operation for all servers in the option file.
Each GNR value represents an option group number or range of
group numbers. The value should be the number at the end of the
group name in the option file. For example, the GNR for a group
named [mysqld17] is 17. To specify a range of numbers, separate
the first and last numbers by a dash. The GNR value 10-13
represents groups [mysqld10] through [mysqld13]. Multiple groups
or group ranges can be specified on the command line, separated
by commas. There must be no whitespace characters (spaces or
tabs) in the GNR list; anything after a whitespace character is
ignored.
This command starts a single server using option group
[mysqld17]:
shell> mysqld_multi start 17
This command stops several servers, using option groups [mysqld8]
and [mysqld10] through [mysqld13]:
shell> mysqld_multi stop 8,10-13
For an example of how you might set up an option file, use this
command:
shell> mysqld_multi --example
mysqld_multi searches for option files as follows:
• With --no-defaults, no option files are read.
• With --defaults-file=file_name, only the named file is read.
• Otherwise, option files in the standard list of locations are
read, including any file named by the
--defaults-extra-file=file_name option, if one is given. (If
the option is given multiple times, the last value is used.)
Option files read are searched for [mysqld_multi] and [mysqldN]
option groups. The [mysqld_multi] group can be used for options
to mysqld_multi itself. [mysqldN] groups can be used for options
passed to specific mysqld instances.
The [mysqld] or [mysqld_safe] groups can be used for common
options read by all instances of mysqld or mysqld_safe. You can
specify a --defaults-file=file_name option to use a different
configuration file for that instance, in which case the [mysqld]
or [mysqld_safe] groups from that file will be used for that
instance.
mysqld_multi supports the following options.
• --help
Display a help message and exit.
• --example
Display a sample option file.
• --log=file_name
Specify the name of the log file. If the file exists, log
output is appended to it.
• --mysqladmin=prog_name
The mysqladmin binary to be used to stop servers.
• --mysqld=prog_name
The mysqld binary to be used. Note that you can specify
mysqld_safe as the value for this option also. If you use
mysqld_safe to start the server, you can include the mysqld
or ledir options in the corresponding [mysqldN] option group.
These options indicate the name of the server that
mysqld_safe should start and the path name of the directory
where the server is located. (See the descriptions for these
options in mysqld_safe(1).) Example:
[mysqld38]
mysqld = mysqld-debug
ledir = /opt/local/mysql/libexec
• --no-log
Print log information to stdout rather than to the log file.
By default, output goes to the log file.
• --password=password
The password of the MariaDB account to use when invoking
mysqladmin. Note that the password value is not optional for
this option, unlike for other MariaDB programs.
• --silent
Silent mode; disable warnings.
• --tcp-ip
Connect to the MariaDB server(s) via the TCP/IP port instead
of the UNIX socket. This affects stopping and reporting. If a
socket file is missing, the server may still be running, but
can be accessed only via the TCP/IP port. By default
connecting is done via the UNIX socket. This option affects
stop and report operations.
• --user=user_name
The user name of the MariaDB account to use when invoking
mysqladmin.
• --verbose
Be more verbose.
• --version
Display version information and exit.
• --wsrep-new-cluster
Bootstrap a cluster.
Some notes about mysqld_multi:
• Most important: Before using mysqld_multi be sure that you
understand the meanings of the options that are passed to the
mysqld servers and why you would want to have separate mysqld
processes. Beware of the dangers of using multiple mysqld
servers with the same data directory. Use separate data
directories, unless you know what you are doing. Starting
multiple servers with the same data directory does not give
you extra performance in a threaded system.
• Important: Make sure that the data directory for each server
is fully accessible to the Unix account that the specific
mysqld process is started as. Do not use the Unix root
account for this, unless you know what you are doing.
• Make sure that the MariaDB account used for stopping the
mysqld servers (with the mysqladmin program) has the same
user name and password for each server. Also, make sure that
the account has the SHUTDOWN privilege. If the servers that
you want to manage have different user names or passwords for
the administrative accounts, you might want to create an
account on each server that has the same user name and
password. For example, you might set up a common multi_admin
account by executing the following commands for each server:
shell> mysql -u root -S /tmp/mysql.sock -p
Enter password:
mysql> GRANT SHUTDOWN ON *.*
-> TO ´multi_admin´@´localhost´ IDENTIFIED BY ´multipass´;
Change the connection parameters appropriately when
connecting to each one. Note that the host name part of the
account name must allow you to connect as multi_admin from
the host where you want to run mysqld_multi.
• The Unix socket file and the TCP/IP port number must be
different for every mysqld. (Alternatively, if the host has
multiple network addresses, you can use --bind-address to
cause different servers to listen to different interfaces.)
• The --pid-file option is very important if you are using
mysqld_safe to start mysqld (for example,
--mysqld=mysqld_safe) Every mysqld should have its own
process ID file. The advantage of using mysqld_safe instead
of mysqld is that mysqld_safe monitors its mysqld process and
restarts it if the process terminates due to a signal sent
using kill -9 or for other reasons, such as a segmentation
fault. Please note that the mysqld_safe script might require
that you start it from a certain place. This means that you
might have to change location to a certain directory before
running mysqld_multi. If you have problems starting, please
see the mysqld_safe script. Check especially the lines:
----------------------------------------------------------------
MY_PWD=`pwd`
# Check if we are starting this relative (for the binary release)
if test -d $MY_PWD/data/mysql -a \
-f ./share/mysql/english/errmsg.sys -a \
-x ./bin/mysqld
----------------------------------------------------------------
The test performed by these lines should be successful, or
you might encounter problems. See mysqld_safe(1).
• You might want to use the --user option for mysqld, but to do
this you need to run the mysqld_multi script as the Unix root
user. Having the option in the option file doesn´t matter;
you just get a warning if you are not the superuser and the
mysqld processes are started under your own Unix account.
The following example shows how you might set up an option file
for use with mysqld_multi. The order in which the mysqld programs
are started or stopped depends on the order in which they appear
in the option file. Group numbers need not form an unbroken
sequence. The first and fifth [mysqldN] groups were intentionally
omitted from the example to illustrate that you can have 'gaps'
in the option file. This gives you more flexibility.
# This file should probably be in your home dir (~/.my.cnf)
# or /etc/my.cnf
# Version 2.1 by Jani Tolonen
[mysqld_multi]
mysqld = /usr/local/bin/mysqld_safe
mysqladmin = /usr/local/bin/mysqladmin
user = multi_admin
password = multipass
[mysqld2]
socket = /tmp/mysql.sock2
port = 3307
pid-file = /usr/local/mysql/var2/hostname.pid2
datadir = /usr/local/mysql/var2
language = /usr/local/share/mysql/english
user = john
[mysqld3]
socket = /tmp/mysql.sock3
port = 3308
pid-file = /usr/local/mysql/var3/hostname.pid3
datadir = /usr/local/mysql/var3
language = /usr/local/share/mysql/swedish
user = monty
[mysqld4]
socket = /tmp/mysql.sock4
port = 3309
pid-file = /usr/local/mysql/var4/hostname.pid4
datadir = /usr/local/mysql/var4
language = /usr/local/share/mysql/estonia
user = tonu
[mysqld6]
socket = /tmp/mysql.sock6
port = 3311
pid-file = /usr/local/mysql/var6/hostname.pid6
datadir = /usr/local/mysql/var6
language = /usr/local/share/mysql/japanese
user = jani
