Mosh (stands for Mobile Shell) is replacement of SSH for remote connections to Unix/Linux systems. It brings a few noticeable advantages over well known SSH connections. In brief, it’s faster and more responsive, especially on long delay and/or unreliable links. Key benefits of Mosh Stays… Read More »Why Mosh is better than SSH?
If you add new physical network interface to the hardware that runs XenServer it won’t appear in XenCenter by default. In order to attach it to VMs or change its settings you’ll need to type in a few commands to XenServer’s CLI. 1. Connect XenServer… Read More »Add physical NIC to XenServer
Citrix XenServer is powerful hypervisor that is based on Linux (Redhat/Centos/Fedora family) and competes with Vmware ESXi and offer wide range of virtualization features for data centers. In general you can do a bare-metal installation of XenServer to your hardware server and create multiple virtual… Read More »Attach ISO image stored in XenServer local storage
In this post you will find top open source software for IP address management (IPAM). If you are sysadmin at organization that holds pool of IP addresses and allocates its parts to clients then you must use IP address management tools to track used, reserved, allocated… Read More »Top Open Source IP Address Management Software
Linux system monitoring is one of the most important tasks for every sysadmin: it is crucial to know everything about system including CPU load, network traffic statistics, memory consumption, logged in users, availability of disk free space or service. And it’s inevitable that something breaks… Read More »Top 5 Linux Monitoring Tools. Web Based.
As any other monitoring system Nagios can produce false alarms. Usually it happens when Nagios fails to get the reply from the host being monitored during some pre-defined timeout. In order to mark service as down Nagios does three checks and if all of them… Read More »Fix socket timeouts in Nagios
Nfsen is open source sensor: it accepts netflow data from multiple netflow probes (servers, routers, vpn concentrators etc) and then visualizes it into human readable form. So using Nfsen you can see traffic statistics of every network device in your network in one place (actually Nfsen provides much more features).
By default Nfsen makes it possible to see only inbound and outbound traffic statistics but no protocol breakdown or any traffic classification. In the meantime it’s always useful to know what network applications are eating the bandwidth to understand if that fits baseline or not and take necessary actions. For example, if you’re monitoring Linux server which primary task is to host some website but in Nfsen you see that it generates 90% of SSH traffic and only 10% of web traffic then it would be reasonable idea to check if somebody is trying to brute force SSH password and stop that activity. In other words it’s better to have traffic statistics classified. In this article I’ll tell you how to enable traffic classification in Nfsen.
Some time ago I found it pretty useful to configure Nagios monitoring system to send me a phone call in case of some critical problem. If some mission critical application goes down at night most probably you’ll miss an e-mail or sms notifying about that… Read More »Phone call as Nagios notification
Using nfsen it is possible to view IP traffic statistics on Linux interfaces including the graphs showing data sent and received (see the screenshot to the right) as well as historical information about all data transfers. So after you’ve configured nfsen and nfdump to monitor… Read More »Install nfdump and nfsen netflow tools in Linux
Today I’d like to describe setup of sendmail that allows to establish receiving of e-mails for certain domain and sort incoming messages between virtual users. Those users must be able to fetch received e-mails via POP3 or IMAP protocols with or without TLS encryption. The… Read More »Sendmail for virtual users with procmail, spamassassin and dovecot