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rsync command

Occasionally, rsync is too slow when transferring a very large number of files. This article discusses a workaround. Recently I had to copy about 10 TByte of data from one server to another. Normally I would use rsync and just let it run for whatever time it takes, but for this particular system I could […]

CentOS / RHEL 7 : Enable NTP to start at boot after fresh install (disable chrony)

Chrony is introduced as new NTP client to replace the ntp as the default time syncing package since RHEL7, so if you configure NTP during the installation process, it just enables the chronyd service, not ntpd service.

# systemclt status ntpd.service ntpd.service – Network Time Service Loaded: loaded (/usr/lib/systemd/system/ntpd.service; enabled) Active: inactive (dead) Even when […]

CentOS / RHEL 7 : Configuring NTP using chrony

– Chrony provides another implementation of NTP. – Chrony is designed for systems that are often powered down or disconnected from the network. – The main configuration file is /etc/chrony.conf. – Parameters are similar to those in the /etc/ntp.conf file. – chronyd is the daemon that runs in user space. – chronyc is a command-line […]

CentOS / RHEL 7 : Tips on Troubleshooting NTP / chrony Issues

The chrony service does not change the time The often misconception is that the chrony service is setting the time to the one given by the NTP server. This is incorrect – what actually happens is that based on the answer from the NTP server, chrony just tells the system clock to go faster […]

RHEL 7 – RHCSA Notes – input / output redirection

Three standard file descriptors :

1. stdin 0 – Standard input to the program. 2. stdout 1 – Standard output from the program. 3. stderr 2 – Standard error output from the program. PURPOSE COMMAND redirect std output to filename > filename or 1> filename append std out to filename >> filename append std […]

CentOS / RHEL 7 : Configuring static IP adress using network interface configuration files

There are various ways you can configure an IP address in RHEL 7. The posts discusses the use of network interface configuration files to configure the IP address. Each physical network device has an associated network interface configuration file. Network interface configuration files are located in the /etc/sysconfig/network-scripts directory.

1. Use the ip addr command […]

CentOS / RHEL 7 : How to Install GUI

For new installation of RHEL 7 ,GUI doesn’t come with default installation. If you do not click on the “Software Selection” link and pick “server with GUI” then there will be no GUI after reboot, only “Base Environment ” will be installed.

To enable GUI after system installation, you can use following method.

Installing the […]

CentOS / RHEL 7 : How to extract initramfs image and edit/view it

In some cases you may want to extract the initramfs image file to check built-in contents. This post provides steps to extract initramfs image files for RHEL 7. Unlike previous version, on RHEL 7 using cpio command for the initramfs image file will not extract all files (or will give some error). For example:

# […]

CentOS / RHEL 7 : Beginners guide to systemd service units

Previous versions of Oracle Linux use init scripts located in the /etc/rc.d/init directory to start and stop services. In RHEL 7, these init scripts have been replaced with systemd service units. Service units have a .service extension. Use the systemctl command to list all loaded service units:

# systemctl list-units –type service –all UNIT LOAD […]

RHEL 7 – RHCSA Notes : Configure a system to use time services

RHEL 7 has 3 command-line utilities to configure the system date and time: 1. date 2. hwclock 3. timedatectl

date command

Use the date command to display or set the system date and time. Run the date command with no arguments to display the current date and time:

# date Mon Sep 12 19:41:40 IST […]

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