Databases, Systems & Networks

Source: Xmodulo

Have you ever wanted to live stream a video feed from your webcam for someone else? You could use any existing video chat software such as Skype, Google+ Hangouts. However, if you do not want to rely on any third-party streaming infrastructure, you can set up your own webcam streaming server in house.

In this tutorial, I will describe how to live stream video from webcam by using VLC. VLC is an open-source, cross platform media player which can handle virtually all video and audio formats. VLC can also run as a streaming server supporting various streaming protocol such as RTP, HTTP, RTSP, etc.

Before attempting to set up webcam streaming on your own, you need to understand the huge potential security risk of streaming a webcam over the Internet. Anyone can tap into your streaming feed unless you properly access control the streaming server, and encrypt the streaming traffic. I’ll briefly mention several security protections against threats towards the end of the tutorial.

Install VLC on Linux

Before setting up a streaming server with VLC, install VLC first.

To install VLC on Debian, Ubuntu or Linux Mint:

To install VLC on Fedora, first enable RPM Fusion’s free repository, and then run:

To install VLC on CentOS or RHEL 6, first set up EPEL repository, and then use the following commands:

Verify Webcam Device on VLC

Next, verify whether a webcam device is successfully detected on your Linux system and VLC.

To do so, first find out the device name of your webcam with the following command. In this example, the device name of the webcam is /dev/video0.

/dev/video0

Now use the following command to test video from your webcam. Replace « video0 » with your own device name.

If your webcam is successfully detected by VLC, you should see a video stream of yourself.

Configure Webcam Streaming on VLC

Assuming that your webcam is successfully recognized by VLC, I am going to show how to configure webcam streaming. In this setup, webcam is streamed over HTTP in WMV format.

To configure VLC for webcam streaming, first launch VLC.

Choose « Streaming » from VLC menu.

On the screen, choose webcam/audio device name (e.g., /dev/video0 for webcam, and hw:0,0 for audio). Click on the checkbox of « Show more options ». Make a note of value strings in « MRL » and « Edit Options » fields. We will use these strings later in the tutorial. Click on « Stream » button at the bottom.

Lire la suite…

System administrators (sysadmins) are responsible for day-to-day operations of production systems and services. One of the critical roles of sysadmins is to ensure that operational services are available round the clock. For that, they have to carefully plan backup policies, disaster management strategies, scheduled maintenance, security audits, etc. Like every other discipline, sysadmins have their tools of trade. Utilizing proper tools in the right case at the right time can help maintain the health of operating systems with minimal service interruptions and maximum uptime.

This article will present some of the most popular and useful CLI tools recommended for sysadmins in their day to day activities. If you would like to recommend any useful tool which is not listed here, don’t forget to share it in the comment section.

Network Tools

1. ping: Check end-to-end connectivity (RTT delay, jitter, packet loss) of a remote host with ICMP echo/reply. Useful to check system status and reachability.

2. hping: Network scanning and testing tool that can generate ICMP/TCP/UDP ping packets. Often used for advanced port scanning, firewall testing, manual path MTU discovery and fragmentation testing.

3. traceroute: Discover a layer-3 forwarding path from a local host to a remote destination host with TTL-limited ICMP/UDP/TCP probe packets. Useful to troubleshoot network reachability and routing problems.

4. mtr: A variation of traceroute which characterizes per-hop packet loss/jitter with running statistics. Useful to characterize routing path delays.

5. netcat/socat: A swiss army knife of TCP/IP networking, allowing to read/write byte streams over TCP/UDP. Useful to troubleshoot firewall policies and service availability.

6. dig: DNS troubleshooting tool that can generate forward queries, reverse queries, find authoritative name servers, check CNAME, MX and other DNS records. Can be instructed to query a specific DNS server of your choosing.

7. nslookup: Another DNS checking/troubleshooting tool. Works with all DNS queries and records. Can query a particular DNS server.

8. dnsyo: A DNS testing tool which checks DNS propagation by performing DNS lookup from over a number of open resolvers located across 1,500 different networks around the world.

9. lsof: Show information about files (e.g., regular files, pipes or sockets) which are opened by processes. Useful to monitor processes or users in terms of their open network connections or opened files.

10. iftop: A ncurses-based TUI utility that can be used to monitor in real time bandwidth utilization and network connections for individual network interfaces. Useful to keep track of bandwidth hogging applications, users, destinations and ports.

11. netstat: A network statistics utility that can show status information and statistics about open network connections (TCP/UDP ports, IP addresses), routing tables, TX/RX traffic and protocols. Useful for network related diagnosis and performance tuning.

12. tcpdump: A popular packet sniffer tool based on libpcap packet capture library. Can define packet capturing filters in Berkeley Packet Filters format.

13. tshark: Another CLI packet sniffer software with full compatibility with its GUI counterpart, Wireshark. Supports 1,000 protocols and the list is growing. Useful to troubleshoot, analyze and store information on live packets.

14. ip: A versatile CLI networking tool which is part of iproute2 package. Used to check and modifying routing tables, network device state, and IP tunneling settings. Useful to view routing tables, add/remove static routes, configure network interfaces, and otherwise troubleshoot routing issues.

15. ifup/ifdown: Used to bring up or shut down a particular network interface. Often a preferred alternative to restarting the entire network service.

16. autossh: A program which creates an SSH session and automatically restarts the session should it disconnect. Often useful to create a persistent reverse SSH tunnel across restrictive corporate networks.

17. iperf: A network testing tool which measures maximum bi-directional throughput between a pair of hosts by injecting customizable TCP/UDP data streams in between.

18. elinks/lynx: text-based web browsers for CLI-based server environment.

Lire la suite…

Whether you are in the web hosting business, or run a few web sites on a VPS yourself, chances are you want to display visitor statistics such as top visitors, requested files (dynamic or static), used bandwidth, client browsers, and referring sites, and so forth.

GoAccess is a command-line log analyzer and interactive viewer for Apache or Nginx web server. With this tool, you will not only be able to browse the data mentioned earlier, but also parse the web server logs to dig for further data as well – and all of this within a terminal window in real time. Since as of today most web servers use either a Debian derivative or a Red Hat based distribution as the underlying operating system, I will show you how to install and use GoAccess in Debian and CentOS.

Installing GoAccess on Linux

In Debian, Ubuntu and derivatives, run the following command to install GoAccess:

# aptitude install goaccess

In CentOS, you’ll need to enable the EPEL repository and then:

# yum install goaccess

In Fedora, simply use yum command:

# yum install goaccess

If you want to install GoAccess from the source to enable further options (such as GeoIP location), install required dependencies for your operating system, and then follow these steps:

# wget http://tar.goaccess.io/goaccess-0.8.5.tar.gz
# tar -xzvf goaccess-0.8.5.tar.gz
# cd goaccess-0.8.5/
# ./configure --enable-geoip
# make
# make install

That will install version 0.8.5, but you can always verify what is the latest version in the Downloads page of the project’s web site.

Since GoAccess does not require any further configurations, once it’s installed you are ready to go.

Running GoAccess

To start using GoAccess, just run it against your Apache access log.

For Debian and derivatives:

# goaccess -f /var/log/apache2/access.log

For Red Hat based distros:

# goaccess -f /var/log/httpd/access_log

When you first launch GoAccess, you will be presented with the following screen to choose the date and log format. As explained, you can toggle between options using the spacebar and proceed with F10. As for the date and log formats, you may want to refer to the Apache documentation if you need to refresh your memory.

In this case, Choose Common Log Format (CLF):

and then press F10. You will be presented with the statistics screen. For the sake of brevity, only the header, which shows the summary of the log file, is shown in the next image:

Lire la suite…

There are many traffic monitoring tools available on Linux, which can monitor/classify network traffic, and report real-time traffic statistics in fancy user interfaces. Most of these tools (e.g., ntopng, iftop) are powered by libpcap, which is a packet capture library used to monitor network traffic in user space. Despite their versatility, however, libpcap-based network monitoring tools cannot scale to handle traffic on multi Gigabit rate network interfaces, due to the overhead associated with user-space packet capture.

In this tutorial, I will present simple shell scripts that can monitor network traffic on per-interface basis, without relying on slow libpcap library. These scripts are fast enough to support multi Gigabit rates, but only suitable if you are interested in « aggregate » network statistics on per interface basis.

The secret for the scripts lies in sysfs virtual filesystem which is used by the kernel to export device- or driver-related information to user space. Network interface related statistics are exported via /sys/class/net/<ethX>/statistics.

For example, the statistics on eth0 interface are found in these files:

• /sys/class/net/eth0/statistics/rx_packets: number of packets received
• /sys/class/net/eth0/statistics/tx_packets: number of packets transmitted
• /sys/class/net/eth0/statistics/rx_bytes: number of bytes received
• /sys/class/net/eth0/statistics/tx_bytes: number of bytes transmitted
• /sys/class/net/eth0/statistics/rx_dropped: number of packets dropped while received
• /sys/class/net/eth0/statistics/tx_dropped: number of packets dropped while transmitted

The numbers stored in the files are automatically refreshed in real-time by the kernel. Therefore, you can write scripts that calculate traffic statistics based on these files.

The following are two such scripts (thanks to joemiller). The first script counts the number of packets per second, received (RX) or sent (TX) on an interface, while the latter scripts measures the network bandwidth of incoming (RX) and outgoing (TX) traffic on an interface. For these scripts to work, you do not need to install anything.

Measure Packets per Second on an Interface

#!/bin/bash
INTERVAL="1"  # update interval in seconds
if [ -z "$1" ]; then
        echo
        echo usage: $0 [network-interface]
        echo
        echo e.g. $0 eth0
        echo
        echo shows packets-per-second
        exit
fi

IF=$1

while true
do
        R1=`cat /sys/class/net/$1/statistics/rx_packets`
        T1=`cat /sys/class/net/$1/statistics/tx_packets`
        sleep $INTERVAL
        R2=`cat /sys/class/net/$1/statistics/rx_packets`
        T2=`cat /sys/class/net/$1/statistics/tx_packets`
        TXPPS=`expr $T2 - $T1`
        RXPPS=`expr $R2 - $R1`
        echo "TX $1: $TXPPS pkts/s RX $1: $RXPPS pkts/s"
done

Measure Network Bandwidth on an Interface

#!/bin/bash
 
INTERVAL="1" # update interval in seconds
 
if [ -z "$1" ]; then
 echo
 echo usage: $0 [network-interface]
 echo
 echo e.g. $0 eth0
 echo
 exit
fi
 
IF=$1
 
while true
do
 R1=`cat /sys/class/net/$1/statistics/rx_bytes`
 T1=`cat /sys/class/net/$1/statistics/tx_bytes`
 sleep $INTERVAL
 R2=`cat /sys/class/net/$1/statistics/rx_bytes`
 T2=`cat /sys/class/net/$1/statistics/tx_bytes`
 TBPS=`expr $T2 - $T1`
 RBPS=`expr $R2 - $R1`
 TKBPS=`expr $TBPS / 1024`
 RKBPS=`expr $RBPS / 1024`
 echo "TX $1: $TKBPS kB/s RX $1: $RKBPS kB/s"
done