Sync an accurate time using ntpdate on RHEL7 Linux server

To sync a correct time on your Redhat server with a NTP publicly available time servers first you need to install ntpdate package:

[root@rhel7 ~]# yum install ntpdate

To check your current time use date command:

[root@rhel7 ~]# date
Thu Sep  4 17:20:42 WST 2014

Next, we can use pool.ntp.org timeserver to synchronize our time. This is be done with ntpdate command:

[root@rhel7 ~]# ntpdate pool.ntp.org
11 Dec 06:08:13 ntpdate[2225]: step time server 173.230.144.109 offset 8426822.014383 sec

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Update GRUB2 menu timeout on RHEL 7 Linux

The default settings for the GRUB2 timeout menu selection during the system boot is 5 seconds. To change this value open /etc/default/grub grub default config file. The content of the file looks similar the the one shown below:

GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="rd.lvm.lv=rhel/root crashkernel=auto  \ 
rd.lvm.lv=rhel/swap vconsole.font=latarcyrheb-sun16 vconsole.keymap=us rhgb quiet"
GRUB_DISABLE_RECOVERY="true"

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Persistent/Automatic after reboot kernel module loading on CentOS/Redhat Linux

This config will describe a procedure on how to persistently load kernel modules during a boot time on CentOS or Redhat Linux system. In the below commands will use nf_conntrack_pptp as a sample module. Replace the name of this module with a module name you wish to load.

First, create a script within /etc/sysconfig/modules/ directory with a file extension modules. Where the name of the script can be any name of your choice. In our case the script will be called nf_conntrack_pptp.modules. Enter a following code into your new nf_conntrack_pptp.modules script while replacing the name of the module with the one you wish to load:

#!/bin/sh
exec /sbin/modprobe nf_conntrack_pptp  >/dev/null 2>&1

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memtest+ redhat 7 grub menu available

Installation of Memtest+ RAM memory test tool on Redhat 7 Linux

Installation of Memtest+ RAM memory test tool on Redhat 7 Linux

Memtest is a quite handy tool when troubleshooting hardware problem and specifically problems related to Random Access Memory (RAM). After installation the memtest+ tool will become available among other boot options. To install memtest+ on RHEL 7 Linux server execute the following linux command:

# yum install memtest86+
...
Running transaction
  Installing : memtest86+-4.20-12.el7.x86_64      1/1 
  Verifying  : memtest86+-4.20-12.el7.x86_64      1/1 

Installed:
  memtest86+.x86_64 0:4.20-12.el7

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Monitor CPU temperature on Redhat 7 Linux

How to monitor a CPU temperature on Redhat 7 Linux system

Here is a short config to show you how to display and monitor CPU temperature on a Linux system running Redhat 7 Linux. First we need to install lm_sensors:

# yum install lm_sensors

Next, use sensors command to display CPU temperature:

$ sensors | grep Core
Core 0:         +43.0°C  (high = +86.0°C, crit = +100.0°C)
Core 1:         +43.0°C  (high = +86.0°C, crit = +100.0°C)

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How to install, manage, start and autostart ssh service on RHEL 7 Linux

systemctl command is used on RedHat 7 linux to manage services system wide. It allows administrators to manage ssh service to start, restart, stop or enable autoload after system startup.

In install ssh service on your RHEL 7 linux run a following linux command:

# yum install openssh

By defalt SSH service or to be more precise sshd ( daemon ) is disabled. Once the opensshd package installed, you can check the status of SSHD service by using the below command:

# systemctl status sshd
sshd.service - OpenSSH server daemon
   Loaded: loaded (/usr/lib/systemd/system/sshd.service; disabled)
   Active: inactive (dead)

To start ssh daemon (sshd) on RHEL 7 run:

systemctl start sshd

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How to reset the root password in RHEL7/CentOS7/Scientific Linux 7- based systems

Objective

Resetting the root password in RHEL7/CentOS7/Scientific Linux 7

Requirements

RHEL7 / CentOS7 / Scientific Linux 7

Difficulty

MODERATE

Instructions

Things have changed in the RHEL7 world and so has the preferred way of resetting the root password. Although the old way of interrupting the boot process (init=/bin/bash) still works, it is no longer bulletproof and recommended.
‘Systemd’ uses ‘rd.break’ to interrupt the boot. Let’s have a quick walk through the whole procedure.

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