Mysql – How to take backup of thesql databases from the crashed server

Do not mess with the mysql db. There is a lot more going on there than just the users table. Your best bet is the "SHOW GRANTS FOR" command. I have a lot of CLI maintenance aliases and functions in my .bashrc (actually my .bash_aliases that I source in my .bashrc). This function:

mygrants()
{
  mysql -B -N $@ -e "SELECT DISTINCT CONCAT(
    'SHOW GRANTS FOR \'', user, '\'@\'', host, '\';'
    ) AS query FROM mysql.user" | \
  mysql $@ | \
  sed 's/\(GRANT .*\)/\1;/;s/^\(Grants for .*\)/## \1 ##/;/##/{x;p;x;}'
}

The first mysql command uses SQL to generate valid SQL which is piped to the second mysql command. The output is then piped through sed to add pretty comments.

The $@ in the command will allow you to call it as: mygrants --host=prod-db1 --user=admin --password=secret

You can use your full unix tool kit on this like so:

mygrants --host=prod-db1 --user=admin --password=secret | grep rails_admin | mysql --host=staging-db1 --user=admin --password=secret

That is THE right way to move users. Your MySQL ACL is modified with pure SQL.

Best practices depends on what do you need to recover. You definitely should backup to different storage, ideally in different geolocation. I have this little script, which detects all databases and backup each database to separated file, so I can recover only one database.

#!/bin/bash
echo "Starting..."
ROOTDIR="/backup/mysql/es2"
YEAR=`date +%Y`
MONTH=`date +%m`
DAY=`date +%d`
HOUR=`date +%H`
SERVER="mysql.local"
BLACKLIST="information_schema performance_schema"
if [ ! -d "$ROOTDIR/$YEAR/$MONTH/$DAY/$HOUR" ]; then
    mkdir -p "$ROOTDIR/$YEAR/$MONTH/$DAY/$HOUR"
fi
echo "running dump"
dblist=`mysql -u backuper -pXXXXXXXXXXX -h $SERVER -e "show databases" | sed -n '2,$ p'`
for db in $dblist; do
    echo "Backuping $db"
    isBl=`echo $BLACKLIST |grep $db`
    if [ $? == 1 ]; then
        mysqldump --single-transaction -u backuper -pXXXXXXXXXX -h $SERVER $db | gzip --best > "$ROOTDIR/$YEAR/$MONTH/$DAY/$HOUR/$db.sql.gz"
        echo "Backup $db ends with return code $?"
    else
        echo "Database $db is on blacklist, skip"
    fi
done

echo "dump completed"

Each backup is keeped in directory structure YEAR/MONTH/DAY/HOUR/DB_NAME.sql.gz. You can specify which DB you don't want to backup in variable BLACKLIST.