The variable can be changed dynamically without restarting the server. Setting the variable in any way (even to the existing value) forces a rotation of the binary log (the intention is to avoid having a single binlog where some events are checksummed and others are not).
When checksums are enabled, replication slaves will check events received over the network for checksum errors, and will stop with an error if a corrupt event is detected.
In addition, the server can be configured to verify checksums in two other places.
One is when reading events from the binlog on the master, for example when sending events to a slave or for something like SHOW BINLOG EVENTS. This is controlled by option master_verify_checksum, and is thus used to detect file system corruption of the binlog files.
The other is when the slave SQL thread reads events from the relay log. This is controlled by the slave_sql_verify_checksum option, and is used to detect file system corruption of slave relay log files.
The mysqlbinlog client program by default does not verify checksums when reading a binlog file, however it can be instructed to do so with the option verify-binlog-checksum:
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