Linux How to use, Tutorials and scripts; Guides

1. Create separte partation for tmp , if you don't have the space to create a fresh /tmp partition on existing drives, you can use the loopback capabilities of the Linux kernel by creating a loopback filesystem that will be mounted as /tmp and can use the same restrictive mount options. To create a 1GB loopback filesystem, execute the following commands. [root@Centos7 ~]# dd if=/dev/zero of=/dev/tmpDIR bs=1024 count=1000000 1000000+0 records in 1000000+0 records out 1024000000 bytes (1.0 GB) copied, 5.32903 seconds, 192 MB/s 2. Backup Current /tmp Directory: Now backup the current /tmp directory using the syntax below which will keep the same permissions for the files currently in /tmp. [root@Centos7 ~]# cp -Rpf /tmp /tmpbak 3.Modify fstab: You should add a line to the end of the /etc/fstab file so the tmp partation so tmp is mounted when the server reboots. /dev/mapper/centos-tmp  /tmp                    xfs     rw,noexec,nosuid,nodev        0 0 /tmp             

1. NTP package is provided by default from Centos  repositories, and can be installed by the following command: [root@Centos7 ~]# yum -y install ntp 2. Configure these lines. [root@Centos7 ~]# vi /etc/ntp.conf # line 18: add the network range you allow to receive requests restrict 172.160.0.0 mask 255.255.0.0 nomodify notrap # change servers for synchronization #server 0.centos.pool.ntp.org iburst #server 1.centos.pool.ntp.org iburst #server 2.centos.pool.ntp.org iburst #server 3.centos.pool.ntp.org iburst server ntp1.example.local iburst server ntp2.example.local iburst 3. Once the installation completes, start the service and configure it so it starts automatically each time the server boots: [root@Centos7 ~]# systemctl start ntpd [root@Centos7 ~]# systemctl enable ntpd 4. Add the NTP service in firewall [root@Centos7 ~]# firewall-cmd --add-service=ntp --permanent success [root@Centos7 ~]# firewall-cmd --reload success 5. To get a basic report you can u

MySql - Convert InnoDB to MyISAM Storage Engine of Database To convert Database InnoDB Tables to MyISAM steps follow these steps 1. Take the backup of Mysql database [root@Centos7 ]# mysqldump -f --opt mysqldb > /usr/mysqldb.sql 2. Convert the ENGINE from InnoDB to MYISAM  by using below commans. [root@Centos7 ]#mysql -u username -p -e "SELECT concat('ALTER TABLE ', TABLE_NAME,' ENGINE=MYISAM;') FROM Information_schema.TABLES WHERE TABLE_SCHEMA = 'db_name' AND ENGINE = 'InnoDB' AND TABLE_TYPE = 'BASE TABLE'" | tail -n+2 >> /root/MYISAM.sql Note : Update  username and db_name values with your own values. 3. mport that MYISAM.sql file into INNODB database [root@Centos7 ]# mysql -u username -p mysqldb < /root/MYISAM.sql 4. Make it permanent, add to my.cnf default-storage-engine= MyISAM

How to scan new iSCSI disks in Linux ? 1.First check which are the existing disk available on linux server from fdisk. [root@Centos7 ~]# fdisk -l 2>/dev/null | egrep '^Disk' | egrep -v 'dm-|type|identifier' Disk /dev/xvda: 53.7 GB, 53687091200 bytes, 104857600 sectors Disk /dev/mapper/cl-root: 10.7 GB, 10737418240 bytes, 20971520 sectors Disk /dev/mapper/cl-swap: 5368 MB, 5368709120 bytes, 10485760 sectors Disk /dev/mapper/cl-usr: 10.7 GB, 10737418240 bytes, 20971520 sectors Disk /dev/mapper/cl-home: 2147 MB, 2147483648 bytes, 4194304 sectors Disk /dev/mapper/cl-var: 5444 MB, 5444206592 bytes, 10633216 sectors Disk /dev/mapper/cl-tmp: 2147 MB, 2147483648 bytes, 4194304 sectors 2.Find out how many SCSI controller configured. [root@Centos7 ~]# ls -l /sys/class/scsi_host/ total 0 lrwxrwxrwx 1 root root 0 Dec 11 12:09 host0 -> ../../devices/pci0000:00/0000:00:01.1/ata1/host0/scsi_host/host0 lrwxrwxrwx 1 root root 0 Dec 11 12:09 host1 -> ../../dev

Configuring manual or automatic node login with iSCSI 1. Install the software package: [root@Centos7 ~]# yum -y install iscsi-initiator-utils 2. Configure the iqn name for the initiator: [root@Centos7 ~]# cat /etc/iscsi/initiatorname.iscsi InitiatorName=iqn.2017-12.com.centos7:Centos7 3. Edit the iSCSI initiator configuration: # vi /etc/iscsi/iscsid.conf # To manually startup the session set to "manual". The default is automatic. node.startup = automatic # To enable CHAP authentication node.session.auth.authmethod = CHAP # To set a CHAP username and password for initiator node.session.auth.username = iscsiadmin node.session.auth.password = P@$$w0rd 4. Start iSCSI initiator daemon: [root@Centos7 ~]# systemctl start iscsi [root@Centos7 ~]# systemctl enable iscsi 5.Discovering targets in our iSCSI server: [root@Centos7 ~]# iscsiadm --mode discovery -t sendtargets --portal 172.16.20.90 172.16.20.90:3260,1 iqn.2004-04.com.sanstorage:tvs-671:iscsi.sa