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Archives for October 2016

ifconfig command not found – CentOS/RHEL 7

by admin

Problem : ifconfig is missing in the Minimal Install of Red Hat Enterprise Linux 7 (RHEL 7): # ifconfig -bash: ifconfig: command not found Solution In 2009, Red Hat decided to deprecate ifconfig as the default command line network interface management utility, because the “net-tools” package (which provides ifconfig) did not support InfiniBand addresses (commonly […]

Filed Under: CentOS/RHEL 7

CentOS / RHEL : Beginners guide to cron

by admin

Cron is a time-based job scheduler, it is configured it to run commands at given times or intervals. Each User has a cron table which defines what to execute and at what interval. crontab command is used to create, modify and view cron jobs. Configuration files and directories – Cron is controlled by a set […]

Filed Under: Linux

How to mount an iso file in Linux

by admin

ISO files are whole disk images. They are a single image file that are used for burning to CD-ROM. In order to access the files inside the iso file, you need to mount it as a ‘Loop Device’. A loop device, vnd (vnode disk), or lofi (loopback file interface) is a pseudo-device that makes a […]

Filed Under: Linux

How to Get the Number of vCPUs that Oracle VM Guest can get in Oracle VM

by admin

On an x86-based system, a CPU core (no hyperthreading enabled) or a CPU thread (hyperthreading enabled) within a core is presented as a physical CPU by the hypervisor or the bare metal operating system. vCPUs (virtual CPUs) are exposed to the guest virtual machine as CPUs. The guest schedules applications on these vCPUs, and the […]

Filed Under: Oracle VM

How to Move a Datafile from Filesystem to ASM Using ASMCMD CP Command

by admin

Question : A datafile was wrongly added on file system instead of ASM diskgroup. How to move it to the ASM disk group again? Answer : 1) Make sure the datafile to be moved is OFFLINE before proceeding : SQL> alter system switch logfile; System altered. SQL> select file_name, file_id from dba_data_files; FILE_NAME FILE_ID ——————— […]

Filed Under: ASM, oracle

CentOS / RHEL 7 : How to configure serial getty with systemd

by admin

With SysV init, by default, getty processes are started on the first six virtual consoles. They can be accessed with the Ctrl+Alt+F1 to Ctrl+Alt+F6 key combination. systemd starts the getty processes only when needed. That means, only after you change to, for instance, the second virtual terminal by pressing Ctrl+Alt+F2 is the getty process started […]

Filed Under: CentOS/RHEL 7

CentOS / RHEL 7 : How to sync chrony to local clock

by admin

Question : How to sync chrony to the local clock. Answer : When the chrony service starts, there are some settings in the /etc/chrony/chrony.conf file that tells it to actually set the time if specific conditions occur. Below procedure lts you set the local clock as the source for chrony to synchronize the time. 1. […]

Filed Under: CentOS/RHEL 7

CentOS / RHEL 7 : Chrony V/s NTP (Differences Between ntpd and chronyd)

by admin

Chosing between Chrony and NTP – In RHEL 7 ntpd is replaced by chronyd as the default network time protocol daemon. – Basic configuration for synchronize time and date is stored in the file /etc/chrony.conf. – ntpd is still included in yum repository for customers who need to run an NTP service. – Chrony is […]

Filed Under: CentOS/RHEL 7

CentOS / RHEL : How to delete LVM volume

by admin

If the non-root LVM volume, Volume Group, and Physical Volume used for the LV are no longer required on the system, then it could be removed/deleted using following steps. If the LVM volume is containing any required data, then please make sure to take a backup of that data before proceeding with following steps: In […]

Filed Under: Linux

CentOS / RHEL 7 : How to password protect GRUB2 menu entries

by admin

Why should a Linux boot loader have password protection? The following are the primary reasons for password protecting a Linux boot loader: 1. Preventing Access to Single User Mode – If an attacker can boot into single user mode, he becomes the root user. 2. Preventing Access to the GRUB Console – If the machine […]

Filed Under: CentOS/RHEL 7

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