Linux

What is early kdump support? In previous versions of CentOS/RHEL (5/6/7), the kdump service would start very late in the boot sequence. So early crashes information is lost during the booting. Starting CentOS/RHEL 8, a new kdump mechanism called "early kdump support" was introduced to tackle this issue. Early Kdump stores the vmlinuz and initramfs of the crash kernel inside the initramfs of the booting kernel and load them directly into the reserved memory (crashkernel) during early boot … [Read more...] about How to Configure Early-kdump Support Feature in CentOS/RHEL 8

This article explains how to bootup CentOS/RHEL 7 and 8 system into rescue mode or emergency mode. In CentOS/RHEL 7 and 8, both rescue mode and emergency mode are systemd targets which replaced the concept of runlevels in previous CentOS/RHEL versions. Rescue mode is equivalent to single user mode and requires the root password. Rescue mode allows you to repair your system in situations when it is unable to complete a regular booting process. Rescue mode will try to mount all local file … [Read more...] about How to Boot into Rescue Mode or Emergency Mode Through Systemd in CentOS/RHEL 7 and 8

In CentOS/RHEL 8 the network services scripts are not presented anymore(systemctl start network.service or /etc/init.d/network script). In order to restart the network services follow one of these two options. Using Network Manager Use the systemctl command to restart the NetworkManager service/target as shown below: # systemctl restart NetworkManager Using nmcli Tool Note: Run these commands from the GUI or the console, as the network will disable. # nmcli networking off # nmcli … [Read more...] about How to Restart Network Services in CentOS/RHEL 8

dnf has a distro-sync option which is used to synchronize installed packages to the latest available versions. It does the necessary upgrades, downgrades or keeps selected installed packages to match the latest version available from any enabled repository. If no package is given, all installed packages are considered. The distro-sync option of DNF is similar to yum's update option. The following is an example of the distro-sync option: # dnf distro-sync Last metadata expiration check: … [Read more...] about How To Use distro-sync Option With dnf To Upgrade OS (CentOS/RHEL 8)

1. Check the attributes of the FC remote port(s) using the below command: # udevadm info --attribute-walk --path=/sys/class/fc_remote_ports/rport-x:y-z 2. Then create udev rules that match all viable rports by matching the 'role' mentioned in the attributes returned in the above command. For example, create /etc/udev/rules.d/99-tmo.rules and include the below contents. ACTION!="add|change", GOTO="tmo_end" KERNELS=="rport-?*", SUBSYSTEM=="XXXX", ATTR{roles}=="XXXX", … [Read more...] about How to Set “dev_loss_tmo” Value Persistently Using Udev Rule

The Problem While executing: # yum update The following error occurs: One of the configured repositories failed (Unknown), and yum doesn't have enough cached data to continue. At this point the only safe thing yum can do is fail. There are a few ways to work "fix" this: 1. Contact the upstream for the repository and get them to fix the problem. 2. Reconfigure the baseurl/etc. for the repository, to point to a working upstream. This is most often useful if you are using a … [Read more...] about “Could not resolve proxy: https; Unknown error” – error with ‘yum update’

This post will guide the user on how to reinstall a corrupted library via yum. In general, the command below will find which package the corrupted library belongs to: # yum provides \*/[so_file] In this example, we used this error message "/bin/login: error while loading shared libraries: /lib64/libcrypt.so.1: file too short" to identify the corrupted library and the find the package it originally came from: # yum provides \*/libcrypt.so.1 ... glibc-2.17-260.0.17.el7_6.6.x86_64 : The … [Read more...] about How to Reinstall Corrupted Library with yum

The Task Create an LVM snapshot of the root filesystem. Revert Snapshot Changes To An Earlier State. The Solution 1. Before proceeding make sure LVM Volume Group (VG) has enough space for the snapshot. # vgs VG #PV #LV #SN Attr VSize VFree ol 2 2 0 wz--n- 12.00g 1.01g 2. In this example we are creating a root snapshot of 512M. Here "snap" is the snapshot name of a root volume. # lvcreate -L 512M -s -n snap /dev/ol/root Logical volume "snap" created. 3. … [Read more...] about How to Create An LVM Snapshot Of The Root Filesystem And Restore To An Earlier State