SELinux can either be in an enabled or a disabled state. In order to check in which state it is running, we can make use of the getenforce command. There are two modes in which SELinux runs: There are two modes in which SELinux runs: Enforcing: This is the enabled state where all rules are […]
CentOS/RHEL
setenforce Command Examples in Linux
We can change the SELinux modes from enforcing to permissive and vice versa during runtime by using the setenforce command. Before and after changing the SELinux mode, we must ensure the current mode by using the getenforce command. SELinux can either be in an enabled or a disabled state. In order to check in which […]
Sample /etc/kdump.conf configuration file
An image of system memory captured after a kernel crash or hang is called a crash dump. Analyzing a crash dump can give valuable clues for postmortem analyses of kernel problems. However, obtaining a dump after a kernel crash is inherently unreliable because the storage driver responsible for logging data onto the dump device might […]
How to use ipset Command in Linux
IP sets are stored collections of IP addresses, network ranges, MAC addresses, port numbers, and network interface names. The iptables tool can leverage IP sets for more efficient rule matching. For example, let’s say you want to drop traffic that originates from one of several IP address ranges that you know to be malicious. Instead […]
‘error opening class fc_host’ – systool Command Error on CentOS/RHEL 7 and 8
The Problem When running the systool command on CentOS/RHEL 7, the following error message is reported: # systool -c fc_host -v Error opening class fc_host The Solution The error occurs because the scsi_transport_fc module that is responsible for populating the contents of /sys/class/fc_host/ directory is not loaded on the system. 1. Manually load the scsi_transport_fc […]
Dependency failed for NFS server and services
The Problem Attempting to start the NFS (nfs-server.service) on CentOS/RHEL 7 fails as follows: # systemctl status nfs-server.service nfs-server.service – NFS server and services Loaded: loaded (/usr/lib/systemd/system/nfs-server.service; enabled; vendor preset: disabled) Drop-In: /run/systemd/generator/nfs-server.service.d ‘-order-with-mounts.conf Active: inactive (dead) Mar 09 16:17:10 hostname systemd[1]: Dependency failed for NFS server and services. Mar 09 16:17:10 hostname systemd[1]: nfs-server.service: […]
How to Change Default Port of Apache On RHEL/CentOS 7
If you want to change Port in the Apache configuration file it’s easy to do. You can also run a website on a different port rather than the default port. 1. Let’s check which is listening to which service: # nmap -sT -O localhost 2. Check whether Port 8000 is free or not: # lsof […]
How to move /tmp on a separate disk as a separate mount point (Online)
By default when you install any Linux system, the /tmp directory is created automatically under the root partition(‘/’). In some situations, you might want to separate out the /tmp directory on a different mount point or partition altogether. Especially when you want to manage it independently and have a large amount of data to be […]
How to use ldconfig Command in Linux
ldconfig command is used to tell the system about new locations of shared libraries. The uses information provided by the /etc/ld.so.conf configuration file. The ldconfig command creates a cache database of all libraries based on the configuration file. This cache is normally stored in the /etc/ld.so.cache file. Here is the syntax of the ldconfig command: […]
How to Troubleshoot Performance Issues on Linux – Beginners Guide
Following is the list of OS commands apart from basic commands output that are useful in diagnosing the problems at OS end causing the slow performance to the Database or application side. 1. iotop The iotop command is top like utility for disk I/O. It watches I/O usage information output by the Linux kernel (requires […]