Linux

What is peripety and how to install it? Peripety is an auditing utility which logs the changes to file-system and storage configurations on RHEL platforms, the motivation is to provide better tracing of historical changes. The package can be installed with the yum or dnf command: # yum install -y peripety Updating Subscription Management repositories. Unable to read consumer identity This system is not registered to Red Hat Subscription Management. You can use subscription-manager to … [Read more...] about How to Install and Configure peripety utility in CentOS/RHEL 8

The Problem If a command is used with sudo (for e.g. sudo yum clean all) it takes time to execute. [21:29]$ sudo yum clean all [sudo] password for test@geeklab: Loaded plugins: package_upload, product-id, search-disabled-repos, subscription-manager Cleaning repos: production-rhel-x86_64-workstation-7.4 rhel-7-server-rpms Cleaning up everything Maybe you want: rm -rf /var/cache/yum, to also free up space taken by orphaned data from disabled or removed repos [21:33]$ In the above … [Read more...] about Commands used with sudo takes time to execute

RHEL 8's boot loader, Grand Unified Boot Loader (GRUB2) differs from the GRUB2 in RHEL 7. An update to Red Hat Enterprise Linux 8 Beta results in /etc/default/grub changes no longer being included when issuing "grub2-mkconfig -o /boot/grub2/grub.cfg". It seems that at least some options set there are now silently ignored. There are multiple different paths to achieve alterations to the kernel boot parameter option. grub2-editenv The grub2-editenv utility is actually the recommended path … [Read more...] about How to permanently modify the kernel command line in CentOS/RHEL 8?

RHEL 8's boot loader, Grand Unified Boot Loader (GRUB2) differs from the GRUB2 in RHEL 7. An update to Red Hat Enterprise Linux 8 Beta results in /etc/default/grub changes no longer being included when issuing "grub2-mkconfig -o /boot/grub2/grub.cfg". It seems that at least some options set there are now silently ignored. GRUB2, with RHEL 8, builds the various kernel boot entries using a new specification called BLS. The /etc/grub2.cfg file no longer has various menuentry entries, but instead … [Read more...] about Modifying /etc/default/grub – RHEL 7 V/s RHEL 8

Introduction The command strace is used to trace system calls and signals. It is a great tool to use when debugging an application and is often requested by the support engineers to examine certain issues which may arise within the operating system and its programs. Usage To record the system calls issued by running command and output trace information to a file called /tmp/strace.txt, run the following: RHEL 6.7+ and RHEL 7 with strace 4.7 or above: # strace -fvttTyyx -s 4096 -o … [Read more...] about How to use strace to trace system calls made by a command in Linux

The Problem Updating the package iptables to iptables-1.4.7-16.0.3.el6, the service fails to start after a stop. # service iptables stop iptables: Setting chains to policy ACCEPT: filter [ OK ] iptables: Flushing firewall rules: [ OK ] iptables: Unloading modules: [ OK ] # service iptables start iptables: Applying firewall rules: Another app is currently holding the xtables lock. Perhaps you want to use the -w option? [FAILED] The Solution Iptables is being lock, and is creating … [Read more...] about Starting iptables Fails with Error “Another app is currently holding the xtables lock”

The Ask The user wants to limit apache's bandwidth of incoming and outgoing traffic for each client IP addresses using iptables in the CentOS/RHEL box. How can we implement this? The Answer You can limit the bandwidth with "hashlimit" module of iptables. From the man page of "iptables" command: # man iptables ... hashlimit hashlimit uses hash buckets to express a rate-limiting match (like the limit match) for a group of connections using a single iptables rule. … [Read more...] about How to limit bandwidth or traffic for applications using iptables

How do I gain network access to a system for troubleshooting? The network service and/or NetworkManager service are not working. How can I bring networking up to troubleshoot further? How can I bring up an interface for the current boot only? Note: These settings are not persistent and will only work for the current boot. Leaving NetworkManager running, running ifup or ifdown, or starting/stopping/restarting the network service has the potential to change these manually-entered … [Read more...] about How to Manually Bring up the Network or specific interface in CentOS/RHEL (without using NetworkManager or the network service)

The Issue NetworkManager modifies the resolv.conf file and any manual changes there are lost. How to prevent the /etc/resolv.conf file from being overwritten by NetworkManager? The Solution Per the NetworkManager.conf man page: # man NetworkManager.conf ... dns Set the DNS (resolv.conf) processing mode. If the key is unspecified, default is used, unless /etc/resolv.conf is a symlink to /run/systemd/resolve/resolv.conf, /lib/systemd/resolv.conf or … [Read more...] about How to Prevent NetworkManager from Modifying the /etc/resolv.conf file in CentOS/RHEL 7?