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Note: This was verified on a CentOS/RHEL 7 system where SELinux was disabled, iptables and firewalld were turned off. So, the ask here was to have more than one instance of sshd running in the environment. This was purely for testing, you will need to make sure that ports are properly configured in firewalld/iptables services. Follow the steps outlined below to configure multiple instances of ssh with own configuration files. 1. Make a copy of the /etc/ssh/sshd_config file (to be used by … [Read more...] about How to configure multiple ssh instances with own config file (CentOS/RHEL 7)

How to configure multiple instances of sshd in CentOS/RHEL 5,6 Follow the steps below to configure a second instance of sshd: 1. Make a copy of the /etc/ssh/sshd_config file (to be used by the second daemon). # cp /etc/ssh/sshd_config /etc/ssh/sshd-second_config 2. Edit /etc/ssh/sshd-second_config to assign a different port number. Use Port keyword to achieve that. Check manpage of sshd_config for documentation on these keywords. Make sure this port is not in use by any other … [Read more...] about How to configure multiple instances of sshd in CentOS/RHEL 7

Follow the steps below to configure a second instance of the sshd daemon. 1. Make a copy of the /etc/ssh/sshd_config file (to be used by the second daemon). # cp /etc/ssh/sshd_config /etc/ssh/sshd_config-second 2. Edit the /etc/ssh/sshd_config-second file to assign a different port number and pid file. Make sure this port is not in use by any other service # vi /etc/ssh/sshd_config-second Port 5222 PidFile /var/run/sshd-second.pid 3. Make a symlink to the sshd binary (see RHBZ … [Read more...] about How to configure multiple instances of sshd in CentOS/RHEL 5,6

In some environments, it is necessary to backup the partition table in case it is accidentally modified or overwritten. There are two methods to backup the partition table. Using "sfdisk" command 1. Run the command below to backup the partition table on device /dev/sda to /root/partition-sda.img: # sfdisk -d /dev/sda > /root/partition-sda.img 2. You should then copy /root/partition-sda.img to some other storage, for example, a portable USB disk. 3. If the partition is damaged and … [Read more...] about How to backup and restore partition table in CentOS/RHEL/Fedora

Introduction This article shows a test in which a whole Red Hat Enterprise Linux system is backed-up to another disk partition, the files system is then destroyed using fdisk (to simulate a disk failure), and finally, the system is restored successfully. All the steps can be used for CentOS/RHEL 4,5,6,7. NOTE 1: Since there are different kinds of storage, we could not make detailed test on them, and also consider that any mistake will destroy the system and difficult to recover, so we … [Read more...] about How to Backup and Restore a Whole CentOS/RHEL/Fedora system with the dump/restore commands?

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