The Problem The user is unable to run X applications through SSH on a CentOS/RHEL system. The following message is displayed: # xclock Error: Can’t open display: The Solution 1. X11 forwarding is disabled on SSH login unless “-X” option is specified: # ssh -X user@address 2. It may have been disabled in “/etc/ssh/sshd_config” with […]
Archives for November 2018
How to Find Number of CPU Sockets on a CentOS/RHEL System
In our company we have some 3rd-party products installed on CentOS/RHEL systems. The Application team needed to do some accounting on how each product was licensed using number of CPU sockets in the each system. Sadly they did not have any type of CMDB in place to help (Configuration Management Database – something very handy […]
Which network ports are reserved by the Linux Operating System?
For the Linux Operating system, there are 3 different kinds of network service ports: The Well Known Ports (0-1023) – which are reserved for the operating system and core services. The Registered Ports (1024-49151) – which can be used by applications, specific services, and users. The Dynamic and/or Private Ports (49152-65535) There is a standard […]
Linux OS Service ‘portreserve’
The portreserve program aims to help services with well-known ports that lie in the portmap range. It prevents portmap from a real service’s port by occupying it itself, until the real service tells it to release the port (generally in the init script). For example the cups package provides /etc/portreserve/cups. # cat /etc/portreserve/cups ipp In […]
“shutdown” Command Examples in Linux
Introduction In this article, we are going to learn Linux shutdown command with examples. The shutdown command is used to halt/shutdown, reboot the Linux Operating System. When shutdown is entered correctly—as root, and with a valid time argument — it does the following. Notifies all users the system is going down Blocks additional logins Notifies […]
11 Useful “ssh” and “scp” Commands in Linux
Introduction In this post, we are going to learn some useful ssh command and scp command with examples. SSH is a protocol that stands for Secure Shell which is a client-side command tool used to take remote session of Linux system securely. It uses Symmetrical and Asymmetrical encryption method to transfer data over the network. […]
6 Bash Shell Command Line Chaining Operators in Linux
Introduction In this article, I will explain you 6 Bash shell command line Chaining Operators (Linux operator). Now let’s discuss what is chaining operator. Chaining operator is something which helps to run multiple commands at once like we execute a script and task completes automatically. Usually, people use Bash shell command line Chaining Operators (Linux […]
14 Useful “cat” Command Examples in Linux
Intoduction When learning Unix, it’s common to first learn the cat command. An easy abbreviation to remember if you are pet-friendly, this command will concatenate the elements you specify into one package. The easiest way to look at files is to use cat, the concatenate command. In this article, we are going to learn how […]
The System Activity Reporter (sar) Command in Linux
The System Activity Reporter, sar, can display a lot of information about your computer and save that information to files for later analysis. This program and its related tools are part of the sysstat package. When you install sysstat, a file named sysstat is added to the /etc/cron.d/ to call sar automatically. On Debian and […]
Linux OS Service ‘kudzu’
Service Name kudzu Description This executes kudzu, the automatic hardware detection tool developed by Red Hat. “kudzu” detects and configures new and/or changed hardware on a system. It loads the required drivers and unloads redundant drivers. It is configured by default to run at system boot time to determine what hardware has been added or […]