A core dump is a file that contains the memory image of a process when it crashes. By default, core dumps are enabled on most Linux distributions. However, in some cases, you may want to disable core dumps to save disk space or to prevent sensitive data from being written to disk. Here’s how to … Read more

In Bash, you can use the nullglob option to verify if any files with a specific pattern exist in a directory or not. The nullglob option causes the shell to expand patterns to an empty list if no matches are found. Here’s how you can use the nullglob option to verify if *.c files exist … Read more

Blocking traffic from specific countries using iptables can be challenging as IP addresses are not directly tied to a specific country. However, there are several services and databases that provide geo-location information about IP addresses. One way to block traffic from specific countries using iptables is to use the xt_geoip module, which allows you to … Read more

If the yum grouplist and yum groupinstall commands are not working on Redhat Linux, there are a few possible reasons and solutions: Make sure that the yum package manager is installed on your system. You can check this by running the following command: rpm -q yum If yum is not installed, you can install it … Read more

To allow NFS clients to access an NFS server using iptables on Linux, you need to configure the firewall to allow traffic on the appropriate ports. NFS uses a combination of UDP and TCP, so you will need to open both types of traffic. Here are the steps to allow NFS clients to access the … Read more

CentOS and Red Hat Enterprise Linux (RHEL) are two closely related operating systems. CentOS is a community-driven, free and open-source Linux distribution that is built from the same source code as RHEL, but without the branding and licensed components. RHEL is a commercial Linux distribution that is designed for enterprise environments and is backed by … Read more

To add a static route in CentOS, you can use the ip route add command. The syntax of the command is as follows: sudo ip route add destination_network/subnet_mask via gateway_ip Where: destination_network/subnet_mask: Specifies the destination network and subnet mask in CIDR notation (e.g., 192.168.1.0/24). via gateway_ip: Specifies the IP address of the gateway that should … Read more

To configure client SMTP authentication (also known as smarthost authentication) in Postfix, follow these steps: Install the sasl2-bin package if it’s not already installed: sudo apt-get install sasl2-bin Create a new file in /etc/postfix/sasl directory for the authentication credentials. For example: sudo nano /etc/postfix/sasl/sasl_passwd Add the following line to the file, replacing smtp.gmail.com with the … Read more

If you have multiple ISPs and want to use their respective SMTP servers for sending mail from your Postfix server, you can configure authentication for each ISP separately. Here’s how you can set up SMTP authentication for multiple ISPs in Postfix: Install the sasl2-bin package if it’s not already installed: sudo apt-get install sasl2-bin Create … Read more

To temporarily disable an alias in the Bash shell, you can use the \ (backslash) character before the command that the alias points to. This tells the shell to use the actual command instead of the alias. For example, let’s say you have an alias called ll that points to the ls -l command. If … Read more