When it comes to efficiently assigning IP addresses to multiple clients, DHCP is the de facto standard in most networks. In this post, we’ll explore DHCP configuration on Red Hat Enterprise Linux 7 and give an example of how to install it, as well as a few configuration options for dhcpd. With a basic understanding of DHCP, you can get your network up and running almost immediately.
Continue reading Basic DHCP Setup
The idea of using file integrity monitoring to validate your operating system and applications has been around since the late ’90s, with programs like Tripwire. Today, we have a steady stream of companies offering their own version for FIM. However, one consistent and reliable open source solution for Linux is AIDE or the Advanced Intrusion Detection Environment.
Continue reading AIDE – File Integrity Monitoring
Is it possible to get someone’s password in plaintext over ssh? Yes! Surely, this makes no sense when the purpose of ssh is to prevent such a thing. Well, I’m speaking of monitoring the session directly from the server the user is connecting to and not across the network.
Continue reading Sniffing SSH Passwords
By default, the PAM configuration files in Linux allow for null or empty passwords due to the nullok feature. From the manpage,
# man pam_unix
The default action of this module is to not permit the user access to a service if their official password is blank. The nullok argument overrides this default.
Continue reading Disable null passwords
We have all used snmp for many years to help monitor our systems and networks but most admins have been reluctant to migrate to v3 due to the perceived increase in complexity. This post will show you how to quickly and easily enable snmpv3 on your linux system to take advantage of the additional security features to support authentication and privacy.
Install software packages
# yum install net-snmp net-snmp-utils
Continue reading Configuring snmpv3 in Linux
As you know, Linux has a standard set of file access settings based on the concept of read, write, and execute permissions that determine who may access the file or directory in question. The most common way to set and change these permissions is to use commands like chmod, chown or chgrp. While these are powerful commands and have their place, there are occasions where it may be advantageous to fine tune the access to a file or directory. This is where file access control lists or FACLS come in.
Continue reading Linux Lab – Access Control Lists
After setting up your Chrony NTP Server and Client, we are now ready to configure authentication using randomly generated symmetric keys. This is an important option beyond the allow/deny rules within your /etc/chrony.conf file to maintain the integrity of the service.
Continue reading RHEL 8 and Chrony – Part 3
In Part 1, we discussed setting up Chrony from a client perspective. This post will show how to configure the server side and investigate some of the options available within the /etc/chrony.conf configuration file.
Install the Chrony package
Continue reading RHEL 8 and Chrony – Part 2
The Network Time Protocol or NTP is essential for synchronizing system clocks across your environment. Having a reliable and accurate time service is not only important for many different applications but for logging and auditing as well. In RHEL 8, Chrony is used for implementing NTP. In Part 1, we will review setting this service up as a client and look at the basic functionality of the chronyc command to interact with the chrony daemon, chronyd.
Continue reading RHEL 8 and Chrony – Part 1
Sometimes, due to some new specific server requirements, you will find it necessary to increase your swap space. Even if your swap partition is setup as a Logical Volume, your requirements may exceed what is available. This is where creating a new swap file is the best option. In this example, we are going to add a new 12GB swap file.
Check Current Swap Space
Verify the total amount of used and free physical and swap memory with the free command and the -h human-readable flag
# free -ht
total used free shared buff/cache available
Mem: 755G 321G 3.0G 62G 430G 670G
Swap: 4G 1G 3G
Total: 771G 322G 6G
Display the swap usage summary by device using swapon. Same as cat /proc/swaps
Continue reading Add a Swap File to RHEL/CentOS