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

How to install OpenSSL and mod ssl First need to install the openssl and mod ssl and then will generating the certificate to be used. Open a terminal prompt and issue the following command  [root@Centos7 conf.d]# yum install mod_ssl Loaded plugins: fastestmirror, langpacks Loading mirror speeds from cached hostfile  * base: mirror.nbrc.ac.in  * epel: kartolo.sby.datautama.net.id  * extras: mirror.nbrc.ac.in Resolving Dependencies --> Running transaction check ---> Package mod_ssl.x86_64 1:2.4.6-67.el7.centos.5 will be installed --> Finished Dependency Resolution Dependencies Resolved ========================================================================  Package                     Arch                       Version                                     Repository                   Size ======================================================================== Installing:  mod_ssl                     x86_

How to install xrdp on CentOS 7 / RHEL 7 1. First Install Gnome on CentOS 7 2. Install and configure EPEL repository. [root@Centos7 system]# yum install epel-release Loaded plugins: fastestmirror, langpacks base                                                                                                           | 3.6 kB  00:00:00 extras                                                                                                         | 3.4 kB  00:00:00 updates                                                                                                        | 3.4 kB  00:00:00 updates/7/x86_64/primary_db                                                                                    | 2.7 MB  00:00:07 Loading mirror speeds from cached hostfile  * base: ftp.iitm.ac.in  * extras: ftp.iitm.ac.in  * updates: ftp.iitm.ac.in Resolving Dependencies --> Running transaction check ---> Package epel-release.noarch 0:7-9 will be installed --> Finished D

While configuration postfix authentication getting the error status=deferred (delivery temporarily suspended: connect to smtp.office365.com[2603:1026:3:ca::2]:587: Network is unreachable) its because of you were not using IPv6/ wrong settings for ipv6. You can either use IPv4, or correct your IPv6 settings. [root@mailserver postfix]# netstat -nutlap | grep 25 tcp        0      0 0.0.0.0:25              0.0.0.0:*               LISTEN      3956/master tcp        0      0 127.0.0.1:38442         127.0.0.1:3306          ESTABLISHED 2596/httpd [root@mailserver postfix]# vi /etc/postfix/main.cf [root@mailserver postfix]# systemctl restart postfix [root@mailserver postfix]# netstat -nutlap | grep 25 tcp        0      0 0.0.0.0:25              0.0.0.0:*               LISTEN      4079/master tcp        0      0 127.0.0.1:38442         127.0.0.1:3306          ESTABLISHED 2596/httpd tcp6       0      0 :::25                   :::*                    LISTEN      407

Getting the error while running the sudo -s to become root sudo: /usr/bin/sudo must be owned by uid 0 and have the setuid bit set 1.Login the server using root and change the permission of /usr/bin/sudo chmod 4755 /usr/bin/sudo 2. if you do not have root password then reboot the server on single usermode and run these commands. mount -o remount,rw /dev/mapper/lv_root / chown root:root /usr/bin/sudo chmod 4755 /usr/bin/sudo restart

root@HPUX:~# realm join --user=domainuser  windows.local  --install=/ -v  * Resolving: _ldap._tcp.windows.local  * Resolving: windows.local  * Performing LDAP DSE lookup on: 192.16.100.194  * Successfully discovered: windows.local Password for domainuser:  * Assuming packages are installed  * LANG=C /usr/sbin/adcli join --verbose --domain windows.local --domain-realm WINDOWS.LOCAL --domain-controller 192.16.100.194 --login-type user --login-user domainuser --stdin-password  * Using domain name: windows.local  * Calculated computer account name from fqdn: HPUX  * Using domain realm: windows.local  * Sending netlogon pings to domain controller: cldap://192.16.100.194  * Received NetLogon info from: GDCADC001.windows.local  * Wrote out krb5.conf snippet to /var/cache/realmd/adcli-krb5-OYG8o8/krb5.d/adcli-krb5-conf-QbSlJr  * Authenticated as user: domainuser@WINDOWS.LOCAL  ! Couldn't authenticate to active directory: SASL(-1): generic failure: GSSAPI Error: Unspecified

Couldn't join realm: Necessary packages are not installed: sssd-tools sssd libnss-sss libpam-sss adcli root@HPUX:~# realm join --user=domainuser@windows.local  windows.local -v  * Resolving: _ldap._tcp.windows.local  * Resolving: windows.local  * Performing LDAP DSE lookup on: 192.168.20.24  * Successfully discovered: windows.local Password for domainuser@windows.local:  * Unconditionally checking packages  * Resolving required packages  ! Necessary packages are not installed: sssd-tools sssd libnss-sss libpam-sss adcli realm: Couldn't join realm: Necessary packages are not installed: root@HPUX:~# apt-get install sssd-tools sssd libnss-sss libpam-sss adcli Reading package lists... Done Building dependency tree Reading state information... Done adcli is already the newest version (0.8.1-1). libnss-sss is already the newest version (1.13.4-1ubuntu1.7). libpam-sss is already the newest version (1.13.4-1ubuntu1.7). sssd is already the newest version (1.13.4-1u

 EPEL Repository in RHEL/CentOS 7/6 To enable the EPEL repository on CentOS 7.x, RedHat 7.x, or Oracle Linux 7.0/7.1 This section describes how to download and install the EPEL repository. Download the EPEL repository: wget http://download.fedoraproject.org/pub/epel/7/x86_64/e/epel-release-7-2.noarch.rpm Install the EPEL repository: rpm -Uvh epel-release-7*.rpm Or you can use the commands [root@Centos7 ~]# yum install epel-release Loaded plugins: fastestmirror, langpacks epel/x86_64/metalink                    

install nrpe plugins  on Ubuntu & Centos  Find the source code for the latest stable release of NRPE at the NRPE downloads page. Download the latest version to your Nagios server. root@nagiosclient:/# cd /tmp root@nagiosclient:/tmp# wget https://github.com/NagiosEnterprises/nrpe/releases/download/nrpe-3.2.0/nrpe-3.2.0.tar.gz --2017-09-11 14:34:41--  https://github.com/NagiosEnterprises/nrpe/releases/download/nrpe-3.2.0/nrpe-3.2.0.tar.gz Resolving github.com (github.com)... 192.30.255.112, 192.30.255.113 Connecting to github.com (github.com)|192.30.255.112|:443... connected. HTTP request sent, awaiting response... 302 Found Location:  Connecting to github-production-release-asset-2e65be.s3.amazonaws.com (github-production-release-asset-2e65be.s3.amazonaws.com)|54.231.120.35|:443... connected. HTTP request sent, awaiting response... 200 OK Length: 517743 (506K) [application/octet-stream] Saving to: ‘nrpe-3.2.0.tar.gz’ nrpe-3.2.0.tar.gz