How to verify, if cable is connected to the interface in Linux? How to verify physical connection to network on interface in Linux?
If you are away from the server and unable to see if ethernet cable is connected to the particular interface in server, but you have another connection (i.e.: via iLO Console), you can use ethtool to verify physical connectivity on that interface remotely.
Continue reading “How To Detect Physical Interface Connectivity to the Network in Linux”
SELinux (Security Enhanced Linux) is an additional method of Linux system protection. It’s a group of security contexts that determine which process can access which files, directories, ports, etc…
SELinux has three modes:
Enforcing: SELinux protects files, directories, ports against unauthorized access and logs all SELinux events and attempts.
Permissive: SELinux allows all interactions and context violations and logs them. Permissive mode is often used for troubleshooting SELinux.
Disabled: SELinux is completely disabled.
SELinux in Enforcing mode may cause problems accessing files or ports in the system, that’s why it’s good to know how to change it’s mode or even disable it.
Continue reading “How to Disable or Enable SELinux on CentOS / Fedora / RHEL”
You can compare two text files in Linux using the following command-line tools:
– vim / vimdiff
These tools are already installed “out-of-the-box” in most Linux distributions.
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Secure Shell (SSH), besides standard password authentication, gives us the possibility to authenticate using private – public key relation. This allows us access remote systems without typing the password each time we want to connect and the connection is still secure. This method is based on generation of two keys: private key (kept private on our local host), public key (given to any remote host we want to connect to passwordless).
Continue reading “How to Configure Passwordless SSH Login in Linux”
DHCP (Dynamic Host Configuration Protocol) is a network protocol used for dynamically assigning IP addresses for computers attached to the network. Standard port used for DHCP service: 67(UDP).
In this tutorial we will launch dhcp server on CentOS 7 / RHEL 7 and define example subnets.
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RedHat 7 / CentOS 7 unlike previous version 6, doesn’t provide the ability to reset / recover root password in signle-user mode any more. This situation takes place, because RedHat 7 / CentOS 7 uses systemd manager instead of sysVinit / upstart and both systemd targets: rescue.target and emergency.target require root password. That’s why in RedHat 7 / CentOS 7 we need installation disk to boot from.
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RedHat 6 / CentOS 6 system gives us the opportunity to reset root password in case we forget it, on condition that we have a direct access to the machine on which we want to reset root password. Password can be reset after booting the system into single-user mode.
1. Reboot the system
2. At the screen: “Booting Red Hat Enterprise Linux…” or “Booting CentOS…” press any key to display GRUB menu.
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LDAP stands for Lightweight Directory Access Protocol. As the name suggests, it is a lightweight protocol for accessing directory services, specifically X.500-based directory services. OpenLDAP is a free, open source implementation of the Lightweight Directory Access Protocol (LDAP) developed by the OpenLDAP Project. It is released under its own BSD-style license called the OpenLDAP Public License.
In this tutorial we will show you, how to install OpenLDAP server on CentOS 7 / RHEL 7 and create basic configuration in a few simple steps:
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vsftpd (Very Secure File Transfer Protocol Daemon) is lightweight, fast and default FTP server daemon for rpm-based Linux distributions (CentOS/RHEL/Fedora).
We will install vsftpd on CentOS7 with selinux enabled in Enforcing mode.
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Brute Force Attack consists of systematically checking all possible passwords until the correct one is found. If the host is exposed directly to the Internet (WAN) and SSH service is running on the host, it becomes a subject of constant brute force attacks performed by automated scripts like hydra.
To detect SSH brute force attempts on systems running systemd service manager (CentOS7/Fedora21/RHEL7), you can use journalctl command with parameters:
Continue reading “Detect SSH Brute Force Attack and Locate Attacker”