Monitoring network connections certainly can be frustrating, mainly because they can be established and then disappear within a matter of seconds. In this post, we will show you how to achieve a Zen-like approach to monitoring network connections on your servers using a command line–based tool called iftop. iftop is to networks what top is to CPUs. And, in the same way, ifconfig refers to configuring an interface, the friendly iftop stands for “interface top”. Iftop on Solaris 11, an open … [Read more...] about How to measure NIC Performance/Throughput in Solaris 11 using iftop
How to modify the UUID of a Volume Group (VG) or Physical Volume (PV) in CentOS/RHEL
The device node name of a disk (/dev/sda, /dev/hda, /dev/vda, etc.) may change in some situations. For example, after switching cables around or upgrading certain packages, sda & sdc could swap places. This causes problems when /etc/fstab references filesystems by the disk names. Instead, use filesystem UUIDs (universally unique identifiers) or labels. Either of these allow for identifying a filesystem without resorting to ephemeral block device names. Note: UUIDs and labels are not required … [Read more...] about How to modify the UUID of a Volume Group (VG) or Physical Volume (PV) in CentOS/RHEL
10 useful cron examples to schedule jobs in Linux
The GNU/Linux system supports several utilities for scheduling tasks. The cron utility is the most widely supported. It allows you to schedule tasks to be run in the background at regular intervals. The cron utility uses a table (crontab) with a list of scripts or commands to be executed and the time when they are to be executed. Scheduling jobs Normal users can use the crontab command to manage their jobs. This command can be called in four different ways: CommandFunction crontab … [Read more...] about 10 useful cron examples to schedule jobs in Linux
How to install rsyslog7 when rsyslog5 is already installed in CentOS/RHEL
The Problem When attempting to install rsyslog7, it fails with a conflict error with rsyslog. # yum install rsyslog7 ... Resolving Dependencies --> Running transaction check ---> Package rsyslog7.x86_64 0:7.4.10-7.el6 will be installed --> Processing Dependency: libestr.so.0()(64bit) for package: rsyslog7-7.4.10-7.el6.x86_64 --> Running transaction check ---> Package libestr.x86_64 0:0.1.9-2.el6 will be installed --> Processing Conflict: rsyslog7-7.4.10-7.el6.x86_64 conflicts … [Read more...] about How to install rsyslog7 when rsyslog5 is already installed in CentOS/RHEL
Understanding How an Email System Works
E-mail has become an extremely popular communication tool. A solid understanding of email system concept helps system administrators to investigate various kinds of issues with the email system. 1. How does an email travel The diagram below shows a typical sequence of events that takes place when Alice composes a message using her mail user agent (MUA). She types in or selects from an address book, the e-mail address of her correspondent. Then she sends the email. Alice's MUA … [Read more...] about Understanding How an Email System Works
How to kill a process in Linux (kill, killall, pkill, xkill)
Kill command is used to send a signal to a process or to kill a process. We typically use the command "kill -SIGNAL" to send the signal to a process. # kill -[SIGNAL] [Process ID] There are other ways to effectively kill a process — killing a process by name, killing a process by specifying part of the name, killing a process by pointing out the process with cursor etc. All the below kill conventions will send the TERM signal to the specified process. For the signals, either the signal name … [Read more...] about How to kill a process in Linux (kill, killall, pkill, xkill)
HDPCA Practice Exam Questions and AWS Instance Setup Details
Before taking the HDPCA exam, you can get the feel of the exam by using the HDPCA practice exam on AWS cloud. The practice exam is very similar to the actual exam. You can perform 6 tasks for practice on this machine. The recommended instance configuration in AWS is m3.2xlarge which has 30 GB of memory and 8 vCPUs. You can opt for the spot instances if you are on a budget. Environment Details The details of the setup in the HDPCA practice exam AWS machine are as below: A five-node HDP … [Read more...] about HDPCA Practice Exam Questions and AWS Instance Setup Details
HDPCA Exam Objective – Configure HiveServer2 HA ( Part 2 – Configure HA )
Note: This is post is part of the HDPCA exam objective series Hive first started with HiveServer1. However, this version of the Hive server was not very stable. It sometimes suspended or blocked clients' connection quietly. Since version 11, Hive includes a new Hive server called HiveSever2 as an addition to HiveServer1. HiveServer2 is an enhanced Hive server designed for multiclient concurrency and improved authentication. HiveServer2 also supports Beeline as the alternative command-line … [Read more...] about HDPCA Exam Objective – Configure HiveServer2 HA ( Part 2 – Configure HA )
How to configure Capacity Scheduler Queues Using YARN Queue Manager
Note: This is post is part of the HDPCA exam objective series Capacity Scheduler is mainly designed for multitenancy, where multiple organizations collectively fund the cluster based on the computing needs. There is an added benefit that an organization can access any excess capacity not being used by others. This provides elasticity for the organizations in a cost-effective manner. In the previous post, we have seen installing and configuring capacity scheduler. The fundamental unit of … [Read more...] about How to configure Capacity Scheduler Queues Using YARN Queue Manager
How to Create HDFS policies in Ranger
Note: This is post is part of the HDPCA exam objective series Apache Ranger is an application that enables data architects to implement security policies on a big data ecosystem. The goal of this project is to provide a unified way for all Hadoop applications to adhere to the security guidelines that are defined. Here are some of the features of Apache Ranger: Centralized administration Fine grained authorization Standardized authorization Multiple authorization methods Centralized … [Read more...] about How to Create HDFS policies in Ranger