On CentOS/RHEL, it is sometimes complex to determine which portion of the boot sequence takes a long time. There are several different events happening during the boot sequence, and sometimes default level of logs are not sufficient to determine the component causing the issue. In that case, the steps described in this post can be […]
Archives for January 2021
How to display a Custom Kernel Name in GRUB Menu CentOS/RHEL 6
Question: We run dual boot CentOS/RHEL 6 and use 2 kernels for 2 different applications. How can we display a custom kernel name for each application as shown below: CentOS 6.x Choose this boot option to run APP01. CentOS 6.y Choose this boot option to run APP02. This can be easily done using the “title” […]
How to Configure Automatic Package Updates on the Server in CentOS/RHEL 8
It is always advisable to keep the installed packages up to date, especially when it comes to security. In this post, we will see how to setup Automatic Update using the dnf-automatic tool. DNF tool provides automatic notifications of updates, download updates, and then install them automatically by using systemd timers. Below are three systemd […]
Failed to start LSB: Bring up/down networking – On restarting network service CentOS/RHEL (DHCP client)
The Problem Cannot reliably get networking to start on a server when using DHCP: # sudo /etc/init.d/network restart Restarting network (via systemctl): Job for network.service failed because the control process exited with error code. See “systemctl status network.service” and “journalctl -xe” for details. [FAILED] # journalctl -xe Nov 29 18:57:42 hostaname.domain.com dhclient[37653]: exiting. Nov 29 […]
How To Add Timestamps To dmesg Kernel Boot Log in CentOS/RHEL
During problem analysis or day-to-day operation, it is sometimes difficult to determine what exactly slows the system, especially during the boot process. One contributor to this difficulty is output of the following command: # dmesg NET: Registered protocol family 10 ip6_tables: (C) 2000-2006 Netfilter Core Team nf_conntrack version 0.5.0 (16384 buckets, 65536 max) ip_tables: (C) […]
How to disable ICMP redirects on CentOS/RHEL
In this post, we will see how to disable ICMP redirect processing, which may help maintain network connectivity in situations where a confused switch or network server shunts traffic away from the selected path. Disable ICMP Redirect From The Command Line ICMP Redirect processing can be turned off until the next reboot via the command […]
How to Disable IPv6 on Ubuntu 18.04 Bionic Beaver Linux
Ubuntu 18.04 Bionic Beaver Linux enables Internet Protocol Version 6 (IPv6) by default. However, in certain situations, some users may find it desirable to disable IPv6 support or to re-enable it after it has been disabled. Disabling IPv6 support (Permanently) Disable ipv6 built-in kernel module. 1. Edit /etc/default/grub and append ipv6.disable=1 to GRUB_CMDLINE_LINUX and GRUB_CMDLINE_LINUX_DEFAULT […]
How to Capture More Logs in /var/log/dmesg for CentOS/RHEL
Sometimes not all log messages in /var/log/dmesg can be captured after Linux OS/kernel boots up because of too many block devices attached to the server. This post illustrates another way to record all bootup log messages besides configuring the serial console. Basically kernel parameter “log_buf_len” can be configured to increase kernel log buffer size, Name: […]
Unable to Start RDMA Services on CentOS/RHEL 7
The Problem The RDMA service fails to start on CentOS/RHEL 7 machine. ‘journalctl -r’ command shows the below errors: Oct 11 11:01:15 geeklab systemd-modules-load: Failed to insert ‘rds_rdma’: Address family not supported by protocol Oct 11 11:01:15 geeklab systemd-modules-load: Failed to insert ‘rds_rdma’: Address family not supported by protocol Oct 11 11:01:15 geeklab systemd-modules-load: Failed […]