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# Deleting all keys in redis that match a regular expression

# General 
redis-cli [options] KEYS "prefix:*" | xargs redis-cli [options] DEL

# If authorization is needed
redis-cli -a <AUTH> KEYS "prefix:*" | xargs redis-cli -a <AUTH> DEL

# If no authorization is needed
redis-cli KEYS "prefix:*" | xargs redis-cli DEL

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examples:
1). modify file using regular expression pattern single-line mode ( '.' and '\s' match '\n') 
perl -i -p0E 's|(<artifactId>api</artifactId>[^<]+<version>)(bbb)(</version>)|\1a\3|g' pom.xml

2). modify file using regular expression pattern multi-line mode
perl -i -pE 's|(<artifactId>api</artifactId>[^<]+<version>)(bbb)(</version>)|\1a\3|g' pom.xml

3). do not modify file actually, just print the changed contents
perl -p0E 's|(<artifactId>api</artifactId>[^<]+<version>)(bbb)(</version>)|\1a\3|g' pom.xml

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# /etc/krb5.conf

[logging]
 default = FILE:/var/log/krb5libs.log
 kdc = FILE:/var/log/krb5kdc.log
 admin_server = FILE:/var/log/kadmind.log

[libdefaults]
 dns_lookup_realm = false
 ticket_lifetime = 24h

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* install
# yum install postgresql-server postgresql-contrib
# postgresql-setup initdb

* allow passowrd authentication & remote access
# vi /var/lib/pgsql/data/pg_hba.conf
host    all             all             127.0.0.1/32            ident
host    all             all             ::1/128                 ident
->
host    all             all             127.0.0.1/32            md5

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# ls /sys/class/scsi_host/ | while read host ; do echo "- - -" > /sys/class/scsi_host/$host/scan ; done


from
http://wingloon.com/2013/05/07/how-to-detect-a-new-hard-disk-without-rebooting-vmware-linux-guest/

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* install ntp
yum install ntp

* edit /etc/ntp.conf
server 0.pool.ntp.org
server 1.pool.ntp.org
server 2.pool.ntp.org

* enable ntp service
centos 7

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Install tsung centos 7

yum -y install erlang perl perl-RRD-Simple.noarch perl-Log-Log4perl-RRDs.noarch gnuplot perl-Template-Toolkit
wget http://tsung.erlang-projects.org/dist/tsung-1.6.0.tar.gz
tar xfz tsung-1.6.0.tar.gz
cd tsung-1.6.0
./configure && make && make install

mkdir /root/.tsung

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https://mathiasbynens.be/notes/mysql-utf8mb4

my.cnf
...
[client]
default-character-set = utf8mb4

[mysqld]
character-set-server = utf8mb4
collation-server = utf8mb4_unicode_ci

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var objIdMin = ObjectId(Math.floor((new Date('1990/10/10'))/1000).toString(16) + "0000000000000000")
var objIdMax = ObjectId(Math.floor((new Date('2011/10/10'))/1000).toString(16) + "0000000000000000")
db.myCollection.find({_id:{$gt: objIdMin, $lt: objIdMax}})

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1. MySQL5.7+ generates a temporary random password after installation and stored in /var/log/mysqld.log
2. get the temporay password to reset root password
   grep "A temporary password is generated for root" /var/log/mysqld.log
3. a. mysql> uninstall plugin validate_password;
   b. /etc/my.cnf
      validate_password_policy=LOW