If you are interested in learning VIM (VI iMproved) basics, you should try vimtutor,an easy and nice VIM tutorial.
Installation:
apt-get install vim vim-runtimeyum install vim-enhancedUse:
vimtutor [2-letters language code]. Example: vimtutor esEnjoy VIM!
Yesterday, I spent a couple of hours finding out why a HP Deskjet 2050 wasn’t working on a virtualized Windowx XP using VirtualBox. It seems that VirtualBox’s scanner support is far from complete, so some scanners aren’t supported at all. I was lucky and I could manage my scanner to work.
TIP: If you disable the “Enable USB 2.0 (EHCI) Controller”, some scanners may run on a virtualized Windows XP.
Description: to connect your computer to a Cisco device via its console port, you usually need a RJ45 rolled cable. You can use a RJ-45 to DB-9 Female if your computer has a serial port.
To communicate through the serial port with the Cisco device, you need Minicom, a terminal emulator software.
Installation:
sudo apt-get install minicomsudo yum install minicomSteps:
dmesg | grep ttyS
[ 0.485378] serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
[ 0.485739] 00:07: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A
sudo minicomsudo minicom ciscoTip: if you need to send a “Break” through Minicom (on a password recovery operation, for example), use Ctrl+A F .
Description: sometimes you need to force a file system check after you reboot your computer. This can be done in two ways:
If you are going to reboot right now:
sudo shutdown -Fr nowIf you aren’t going to reboot right now:
sudo touch /forcecheckAlternatively, if you want to avoid a file system check, use this command to reboot your machine: sudo shutdown -fr now
The Humble Indie Bundle strikes back. As I did before, I’ve already contributed by purchasing my copies of their cross-platform games (GNU/Linux, Windows, Mac).
I totally recommend them.
Disclaimer: This recipe is focused on SMP computers only.
Description: CPU affinity is a scheduler property that binds a process to a given set of CPUs on the system, so that the system scheduler won’t run this process on any other CPUs. By default, the scheduler tries to keep processes on the same CPU as long as it makes sense for performance reasons, so forcing CPU affinity is useful only in some cases (per processor licensing, testing, broken hardware, etc).
CPU affinity is represented as a bitmask (given in hexadecimal), with the lowest order bit corresponding to the first logical CPU and the highest order bit corresponding to the last logical CPU. Examples:
Taskset is a command used to set or retrieve the CPU affinity of a running process given its PID or to launch a new command with a given CPU affinity.
Installation:
sudo apt-get install util-linuxsudo yum install util-linuxUsage:
taskset -p PIDtaskset -p 1276
pid 1276's current affinity mask: 3
taskset -p MASK PID taskset -p 0x00000001 9030
pid 9030's current affinity mask: 3
pid 9030's new affinity mask: 1
taskset MASK COMMANDYou can check if taskset is working using top and pressing “1” to show all CPUs.
Description: mod_deflate is an Apache module which “provides the DEFLATE output filter that allows output from your server to be compressed before being sent to the client over the network.” (from its web). This means that you save some bandwidth in exchange for some CPU cycles compressing the data your Apache server sends.
Installation: If you have Apache installed, you don’t need additional packages, because this module belongs to the package “apache2.2-common“.
Configuration:
sudo a2enmod deflateAddOutputFilterByType DEFLATE text/html text/plain text/xml text/css application/x-javascript application/javascript application/ecmascript application/rss+xml text/x-js
BrowserMatch ^Mozilla/4 gzip-only-text/html
BrowserMatch ^Mozilla/4\.0[678] no-gzip
BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
sudo /etc/init.d/apache2 restartNOTE: There are some old versions of some browsers which don’t support this kind of compression, although it’s included in RFC 2616 (HTTP/1.1). http-compression.com has more info about it.
The upgrade is similar to the previous ones:
sudo sed -i 's/lucid/maverick/g' /etc/apt/sources.listsudo apt-get update && sudo apt-get -y dist-upgradesudo shutdown -r nowDescription: Although Ganglia “is a scalable distributed monitoring system for high-performance computing systems such as clusters and Grids” (from its web), I’m going to explain how to set up Ganglia as a monitoring system for a group of computers which are neither part of a cluster nor a grid. Ganglia has very low per-node overheads and high concurrency, which makes it perfect to monitor a huge group of servers. I’m going to use one server to collect all data from the nodes. The collector server will run the web front-end for simplicity reasons, although you can install the web front-end on any other server if you need it.
Installation:
yum install ganglia ganglia-gmetad ganglia-web ganglia-gmondyum install ganglia ganglia-gmondConfiguration on the collector server (for example: collector.mycompany.com):
data_source "my servers" 60 localhost
This will collect data from the groups of machines tagged as “my servers” every 60 seconds. It will use localhost as the source of the info.
cluster {
name = "my servers"
owner = "unspecified"
latlong = "unspecified"
url = "unspecified"
}
udp_send_channel {
host = collector.mycompany.com
port = 8649
}
udp_recv_channel {
port = 8649
}
tcp_accept_channel {
port = 8649
}
This allows collector.mycompany.com to receive monitoring data from every node on port 8649(UDP).
service gmetad restartservice gmond restartConfiguration on each node you want to monitor (except collector.mycompany.com):
cluster {
name = "my servers"
owner = "unspecified"
latlong = "unspecified"
url = "unspecified"
}
udp_send_channel {
host = collector.mycompany.com
port = 8649
}
/*udp_recv_channel {
}
tcp_accept_channel {
}*/
This tells gmond to send the info to collector.mycompany.com on port 8649(UDP).
service gmond restart After a few minutes, you will have your monitoring data available through: collector.mycompany.com/ganglia .
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