Specifying Program Options mysql --max_allowed_packet=16M The first command specifies the value in bytes. The second specifies the value in megabytes. For variables that take a numeric value, the value can be given with a suffix of  K ,  M , or  G  to indicate a multiplier of 1024, 1024$^{2}$ or 1024$^{3}$. (For example, when used to set  max_allowed_packet , the suffixes indicate units of kilobytes, megabytes, or gigabytes.) As of MySQL 8.0.14, a suffix can also be  T ,  P , and  E  to indicate a multiplier of 1024$^{4}$, 1024$^{5}$ or 1024$^{6}$. Suffix letters can be uppercase or lowercase. In an option file, variable settings are given without the leading dashes: If you like, underscores in an option name can be specified as dashes. The following option groups are equivalent. Both set the size of the server’s key buffer to 512MB: Or: Suffixes for specifying a value multiplier can be used when setting a variable at program invocation time, but not to set the value with  SET  at runtime. On the other hand, with  SET , you can assign a variable’s value using an expression, which is not true when you set a variable at server startup. For example, the first of the following lines is legal at program invocation time, but the second is not: Conversely, the second of the following lines is legal at runtime, but the first is not: By convention, long forms of options that assign a value are written with an equals ( = ) sign, like this: For options that require a value (that is, not having a default value), the equal sign is not required, and so the following is also valid: In both cases, the  mysql  client attempts to connect to a MySQL server running on the host named “tonfisk”  using an account with the user name “jon” . Due to this behavior, problems can occasionally arise when no value is provided for an option that expects one. Consider the following example, where a user connects to a MySQL server running on host  tonfisk as user  jon : 4.2.2.6 Option Defaults, Options Expecting Values, and the = Sign mysql>  SET GLOBAL max_allowed_packet=16M; mysql>  SET GLOBAL max_allowed_packet=16*1024*1024; mysql --host=tonfisk --user=jon mysql --host tonfisk --user jon shell>  mysql --host 85.224.35.45 --user jon Welcome to the MySQL monitor. Commands end with ; or \g. shell>  mysql --max_allowed_packet=16M shell>  mysql --max_allowed_packet=16*1024*1024 [mysqld] key_buffer_size=512M [mysqld] key-buffer-size=512M [mysql] max_allowed_packet=16777216 [mysql] max_allowed_packet=16M 353