Linux

systemd does not allow ordinary users to start or stop system services. In CentOS/RHEL7, "systemd --user" instances are not started for users therefore user-managed systemd instances are non-functional. But we can use sudo to configure command-sudo rules allowing users and/or groups to trigger certain systemctl commands. Follow the steps outlined below to configure sudo rules for non-root users to run a specific systemctl command. 1. Use the command "visudo" to configure the sudo rules to … [Read more...] about How to manage systemd services with a non-root user

By default, auditd in all versions of Red Hat Enterprise Linux rotates its own log files automatically when they reach a certain size, as determined by the max_log_file setting in auditd.conf (which defaults to 6 megabytes). Replacing auto-rotation based on size with auto-rotation based on time 1. Disable auto-rotation in /etc/audit/auditd.conf based on size with auto-rotation based on time, as shown below: # vi /etc/audit/auditd.conf max_log_file_action = ignore 2. Tell auditd to … [Read more...] about How to Configure audit log rotation with compression based on time instead of size in CentOS/RHEL

Currently, the root filesystem is on a standard partition which can't resize, hence need to move it to lvm on the same disk. Note: Take complete backup before starting this activity and test this steps in test system first. Follow below steps to add move root-filesystem from standard partition to lvm. 1. Create new lv and filesystem for root-filesystem. Logical Volume size should be greater than or equal to the existing root-filesystem. File system type (ext3/ext4) should be same as the … [Read more...] about How to Convert root filesystem from standard partition to LVM in CentOS/RHEL

The Basics RHEL7 moves the resource management settings from the process level to the application level by binding the system of cgroup hierarchies with the systemd unit tree. The old way of configuring cgroup, by means of editing several /etc/cg*.conf files is still available but no longer recommended. Systemd provides three unit types(slice, scope, service) that are used for the purpose of resource control. Handling cgroup with service unit of systemd 1. Customize a service unit for … [Read more...] about How to control resource (cgroup) with systemd for user process group in CentOS/RHEL 7

You can utilize the $PrivDropToUser, $PrivDropToUserID, $PrivDropToGroup, and $PrivDropToGroupID configuration directives to run rsyslog as a non-root user. When these variables are used, rsyslog will start as root, but will drop to the specified user and/or group after initialization. The daemon will then run in accordance with the permissions of the specified user or group. Note: If SELinux is in 'enforcing' mode on your system, additional troubleshooting may be necessary to ensure the … [Read more...] about How to run rsyslog as a non-root user in CentOS/RHEL 7

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