Linux

Some specific applications or processes may need higher resource values than the default systemd assigned values. It's possible to override the default resource limits assigned by systemd. Basically systemd sets the default limits for any process when it starts. For example: # cat /proc/1696/limits | grep "Max locked memory" Max locked memory 65536 65536 bytes From the above example, the Max Locked memory is 64K for the PID 1696, and for some process … [Read more...] about How to Set Resource Limits for a Process with Systemd in CentOS/RHEL 7 and 8

The systemd facility replaces the older System-V initialization scripts from earlier releases. The systemd is an event-driven facility which allows non-dependent subsystems to be started, controlled, or stopped in parallel. Here we explain how to add a custom script to the systemd facility. 1. Write And Debug The Custom Script Typically a systemd script is written as a shell script. Begin by writing your custom script using the normal conventions. We will call our script my-custom-script.sh … [Read more...] about How to add a Custom Script to systemd in CentOS/RHEL 7

Question: How to disable the user list being shown when logging into a CentOS/RHEL 8 system? There are 2 ways to disable the user list being shown on the login screen in CentOS/RHEL 8. Per user Settings Globally Settings for all users Method 1 - Per User Setting In this method, an individual user is removed from the user list which appears on the login screen. So if we disable the user "sandy", it will not appear in the user list while other users will still be there on the … [Read more...] about How to Disable user list on GNOME login screen in CentOS/RHEL 8

Question: How to set the banner shown as part of a console in CentOS/RHEL 8? GNOME console banner is a screen with a certain message that is shown before any user logins into the system using his/her login credentials. Login is performed by the Gnome Display Manager (GDM) tool. The steps to configure the GNOME login screen banner are outlined below. All steps are performed as the root user. 1. Create the GDM profile (if it doesn't exist) in /etc/dconf/profile/gdm which contains the … [Read more...] about How to Configure GNOME Console Login Banner in CentOS/RHEL 7 and 8

Starting from CentOS/RHEL 7, resetting of root password has slightly changed than its earlier versions. Let see in this post how we can recover a lost root password on a CentOS/RHEL 8 machine. Breaking Boot Sequence 1. Reboot the system and interrupt the boot loader sequence by pressing any key. 2. Move the cursor to the entry that needs to be booted. 3. Press e to edit the selected entry. Move the cursor to the kernel command line (the line that starts with linux, it looks like … [Read more...] about How to Reset Root Password in CentOS/RHEL 8

In case you have multiple kernels installed in the system, you can boot from a specific kernel in case of a downgrade or any other requirement. Let's see for the purpose of this blog post, how to revert back to an older kernel in CentOS/RHEL 8. Before moving forward, let's understand how to view the current default kernel system has booted from. View the current default kernel 1. You can view the default kernel level currently set in your system using grubby. grubby is a command line tool … [Read more...] about How to Change the default kernel (boot from old kernel) in CentOS/RHEL 8

Question: Is it possible to limit dnf so that it lists or installs only security updates? How to patch the system only with security errata? This post explains how to list and install security updates using dnf on CentOS/RHEL 8. To list security updates 1. To list advisories about newer versions of installed packages (default): # dnf updateinfo list --security or # dnf updateinfo list --security --available 2. To list advisories about any versions of installed packages: # dnf … [Read more...] about How to list or install only security updates with dnf in CentOS/RHEL 8

When suspending a device using the command dmsetup suspend, any I/O that has already been mapped by the device but has not yet completed will be flushed. For example, lvextend command was executed and for some reason, it did not finish. This will keep the volume in suspended mode and all I/O will be blocked. Most of the time, this indicates a problem with the underlying physical volumes and should be investigated further. How to confirm if PV is SUSPENDED Check for the # dmsetup info … [Read more...] about How to activate a “SUSPENDED” LVM physical volume