Saturday, March 26, 2011
Anu
1: Defrag your databases
Whenever you change the structure of a MySQL database, or remove a lot of data from it, the files can become fragmented resulting in a loss of performance, particularly when running queries. Just remember any time you change the database to run the optimiser:
mysqlcheck -o
You may also find it worth your while to defragment your database tables regularly if you are using VARCHAR fields: these variable-length columns are particularly prone to fragmentation.
2: Quicker emails
Can't afford to waste three seconds locating your email client? Can't be bothered finding the mouse under all those gently rotting mountains of clutter on your desk? Whatever you are doing in KDE, you are only a few keypresses away from sending a mail. Press Alt+F2 to bring up the 'Run command' dialog. Type:
mailto:plop@ploppypants.com
Press return and KMail will automatically fire up, ready for your words of wisdom. You don't even need to fill in the entire email address. This also works for Internet addresses: try typing www.slashdot.org to launch Konqueror.
3: Parallelise your build
If you're running a multiprocessor system (SMP) with a moderate amount of RAM, you can usually see significant benefits by performing a parallel make when building code. Compared to doing serial builds when running make (as is the default), a parallel build is a vast improvement. To tell make to allow more than one child at a time while building, use the -j switch:
make -j4; make -j4 modules
4: Save battery power
You are probably familiar with using hdparm for tuning a hard drive, but it can also save battery life on your laptop, or make life quieter for you by spinning down drives.
hdparm -y /dev/hdb
hdparm -Y /dev/hdb
hdparm -S 36 /dev/hdb
In order, these commands will: cause the drive to switch to Standby mode, switch to Sleep mode, and finally set the Automatic spindown timeout. This last includes a numeric variable, whose units are blocks of 5 seconds (for example, a value of 12 would equal one minute).
Incidentally, this habit of specifying spindown time in blocks of 5 seconds should really be a contender for a special user-friendliness award - there's probably some historical reason for it, but we're stumped. Write in and tell us if you happen to know where it came from!
5: Wireless speed management
The speed at which a piece of radio transmission/receiver equipment can communicate with another depends on how much signal is available. In order to maintain communications as the available signal fades, the radios need to transmit data at a slower rate. Normally, the radios attempt to work out the available signal on their own and automatically select the fastest possible speed.In fringe areas with a barely adequate signal, packets may be needlessly lost while the radios continually renegotiate the link speed. If you can't add more antenna gain, or reposition your equipment to achieve a better enough signal, consider forcing your card to sync at a lower rate. This will mean fewer retries, and can be substantially faster than using a continually flip-flopping link. Each driver has its own method for setting the link speed. In Linux, set the link speed with iwconfig:
iwconfig eth0 rate 2M
This forces the radio to always sync at 2Mbps, even if other speeds are available. You can also set a particular speed as a ceiling, and allow the card to automatically scale to any slower speed, but go no faster. For example, you might use this on the example link above:
iwconfig eth0 rate 5.5M auto
Using the auto directive this way tells the driver to allow speeds up to 5.5Mbps, and to run slower if necessary, but will never try to sync at anything faster. To restore the card to full auto scaling, just specify auto by itself:
iwconfig eth0 rate auto
Cards can generally reach much further at 1Mbps than they can at 11Mbps. There is a difference of 12dB between the 1Mbps and 11Mbps ratings of the Orinoco card - that's four times the potential distance just by dropping the data rate!
6: Unclog open ports
Generating a list of network ports that are in the Listen state on a Linux server is simple with netstat:
root@pctipsbyanu:~# netstat -lnp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:5280 0.0.0.0:* LISTEN 698/perl
tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN 217/httpd
tcp 0 0 10.42.3.2:53 0.0.0.0:* LISTEN 220/named
tcp 0 0 10.42.4.6:53 0.0.0.0:* LISTEN 220/named
tcp 0 0 127.0.0.1:53 0.0.0.0:* LISTEN 220/named
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 200/sshd
udp 0 0 0.0.0.0:32768 0.0.0.0:* 220/named
udp 0 0 10.42.3.2:53 0.0.0.0:* 220/named
udp 0 0 10.42.4.6:53 0.0.0.0:* 220/named
udp 0 0 127.0.0.1:53 0.0.0.0:* 220/named
udp 0 0 0.0.0.0:67 0.0.0.0:* 222/dhcpd
raw 0 0 0.0.0.0:1 0.0.0.0:* 7 222/dhcpd
That shows you that PID 698 is a Perl process that is bound to port 5280. If you're not root, the system won't disclose which programs are running on which ports.
7: Faster Hard drives
You may know that the hdparm tool can be used to speed test your disk and change a few settings. It can also be used to optimise drive performance, and turn on some features that may not be enabled by default. Before we start though, be warned that changing drive options can cause data corruption, so back up all your important data first. Testing speed is done with:
hdparm -Tt /dev/hda
You'll see something like:
/dev/hda:Timing buffer-cache reads: 128 MB in 1.64 seconds =78.05 MB/sec
Timing buffered disk reads: 64 MB in 18.56 seconds = 3.45MB/sec
Now we can try speeding it up. To find out which options your drive is currently set to use, just pass hdparm the device name:
hdparm /dev/hda
/dev/hda:
multcount = 16 (on)
I/O support = 0 (default 16-bit)
unmaskirq = 0 (off)
using_dma = 0 (off)
keepsettings = 0 (off)
readonly = 0 (off)
readahead = 8 (on)
geometry = 40395/16/63, sectors = 40718160, start = 0
This is a fairly default setting. Most distros will opt for safe options that will work with most hardware. To get more speed, you may want to enable dma mode, and certainly adjust I/O support. Most modern computers support mode 3, which is a 32-bit transfer mode that can nearly double throughput. You might want to try
hdparm -c3 -d1/dev/hda
Then rerun the speed check to see the difference. Check out the modes your hardware will support, and the hdparm man pages for how to set them.
8: Uptime on your hands
In computing, wasted resources are resources that could be better spent helping you. Why not run a process that updates the titlebar of your terminal with the current load average in real-time, regardless of what else you're running?
Save this as a script called tl, and save it to your ~/bin directory:
#!/usr/bin/perl -w
use strict;
$|++;
my $host=`/bin/hostname`;
chomp $host;
while(1) {
open(LOAD,"/proc/loadavg") || die "Couldn't open /proc/loadavg: $!\n";
my @load=split(/ /,);
close(LOAD);
print "$host: $load[0] $load[1] $load[2] at ", scalar(localtime);
print "\007";
sleep 2;
}
When you'd like to have your titlebar replaced with the name, load average, and current time of the machine you're logged into, just run tl&. It will happily go on running in the background, even if you're running an interactive program like Vim.
9: Grabbing a screenshot without X
There are plenty of screen-capture tools, but a lot of them are based on X. This leads to a problem when running an X application would interfere with the application you wanted to grab - perhaps a game or even a Linux installer. If you use the venerable ImageMagick import command though, you can grab from an X session via the console. Simply go to a virtual terminal (Ctrl+Alt+F1 for example) and enter the following:
chvt 7; sleep 2; import -display :0.0 -window root sshot1.png; chvt 1;
The chvt command changes the virtual terminal, and the sleep command gives it a while to redraw the screen. The import command then captures the whole display and saves it to a file before the final chvt command sticks you back in the virtual terminal again. Make sure you type the whole command on one line.
This can even work on Linux installers, many of which leave a console running in the background - just load up a floppy/CD with import and the few libraries it requires for a first-rate run-anywhere screen grabber.
10: Access your programs remotely
If you would like to lie in bed with your Linux laptop and access your applications from your Windows machine, you can do this with SSH. You first need to enable the following setting in /etc/ssh/sshd_config:
X11Forwarding yesWe can now run The GIMP on 192.168.0.2 with:ssh -X 192.168.0.2 gimp
Stay in touch for more tips n tricks
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