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#!/bin/sh
# Flush MySQL tables to the disk before the filesystem is frozen.
# At the same time, this keeps a read lock in order to avoid write accesses
# from the other clients until the filesystem is thawed.
MYSQL="/usr/bin/mysql"
MYSQL_OPTS="-uroot" #"-prootpassword"
FIFO=/var/run/mysql-flush.fifo
# Check mysql is installed and the server running
[ -x "$MYSQL" ] && "$MYSQL" $MYSQL_OPTS < /dev/null || exit 0
flush_and_wait() {
printf "FLUSH TABLES WITH READ LOCK \\G\n"
trap 'printf "$(date): $0 is killed\n">&2' HUP INT QUIT ALRM TERM
read < $FIFO
printf "UNLOCK TABLES \\G\n"
rm -f $FIFO
}
case "$1" in
freeze)
mkfifo $FIFO || exit 1
flush_and_wait | "$MYSQL" $MYSQL_OPTS &
# wait until every block is flushed
while [ "$(echo 'SHOW STATUS LIKE "Key_blocks_not_flushed"' |\
"$MYSQL" $MYSQL_OPTS | tail -1 | cut -f 2)" -gt 0 ]; do
sleep 1
done
# for InnoDB, wait until every log is flushed
INNODB_STATUS=$(mktemp /tmp/mysql-flush.XXXXXX)
[ $? -ne 0 ] && exit 2
trap "rm -f $INNODB_STATUS; exit 1" HUP INT QUIT ALRM TERM
while :; do
printf "SHOW ENGINE INNODB STATUS \\G" |\
"$MYSQL" $MYSQL_OPTS > $INNODB_STATUS
LOG_CURRENT=$(grep 'Log sequence number' $INNODB_STATUS |\
tr -s ' ' | cut -d' ' -f4)
LOG_FLUSHED=$(grep 'Log flushed up to' $INNODB_STATUS |\
tr -s ' ' | cut -d' ' -f5)
[ "$LOG_CURRENT" = "$LOG_FLUSHED" ] && break
sleep 1
done
rm -f $INNODB_STATUS
;;
thaw)
[ ! -p $FIFO ] && exit 1
echo > $FIFO
;;
*)
exit 1
;;
esac