Via http://linux.byexamples.com/archives/144/redirect-output-to-multiple-processes/

You already know that if you want to pass the output of a program to the input of another program, you can use the pipe | character.

You now that if you want to write the ouput of a program to the disk and at the same time pass it as input to another program, you can use tee.

But maybe you don’t know that if you want to pass the ouput of a program to multiple programs as input, you can use tee again with a little of subshelling.

# source_program | tee (> program1) (> program2) (> programN)| programN+1

Transifex is a not-so-well-known opensource localization platform, written in Python and running on Django (a Python based application server, if you don’t know it). So, being not so well known, there isn’t a lot of documentation about it, and how to install it under Debian 5 Lenny it’s almost undocumented. So, here we go.

First of all, you have to install some packages. Luckily Lenny has got lot of them, although not all the needed

# aptitude install django python-urlgrabber python-setuptools python-pygments python-openid python-markdown python-httplib2
# aptitude install subversion
# aptitude install python-mysqldb
# aptitude install build-essential python-dev

These should be all the packages needed by Transifex which are available as deb packages. Now let’s install the remaining ones through easy_install

# easy_install django-authopenid django-pagination
# easy_install -f http://transifex.org/files/eggs/ contact_form tagging
# easy_install django-notification
# easy_install mercurial

Now the last package, django_evolution which is, AFAIK, only available as an SVN checkout from Google Code

# svn checkout http://django-evolution.googlecode.com/svn/trunk /tmp/django-evol
# mv /tmp/django-evol/django_evolution /usr/lib/python2.5/site-packages/

Now we can download the Transifex tarball

# cd /tmp && wget http://transifex.org/files/transifex-0.6.tar.gz
# tar xzvf transifex-0.6.tar.gz
# cp -a transifex-0.6/transifex /var/www

Now we have to edit some configuration files located in /var/www/transifex/settings with particular attention to the database backend configuration stored in 20-engines.conf. Take this as example

DATABASE_ENGINE = 'mysql'
DATABASE_NAME = 'transifex'
DATABASE_USER = 'transifex'
DATABASE_PASSWORD = 'secret_password'
DATABASE_HOST = 'ADDRESS-OF-YOUR-DB'             # Set to empty string for local socket
DATABASE_PORT = '3306'             # Set to empty string for default

obviously you must create a database (called ‘transifex’ in this example) in your database server and give full permissions to a dedicated user (called ‘transifex’ with ’secret_password’ as password in this example). You can do it with these commands in your mysql console:

CREATE DATABASE transifex;
GRANT ALL ON transifex.* to 'transifex'@'%' IDENTIFIED BY 'secret_password';

Now we can run the configuration scripts, located in the transifex’s base dir

# cd /var/www/transifex
# ./manage.py syncdb
# ./manage.py txcreatedirs

Now we can execute a server instance, listening on address $IPADDRESS and port 8088,  and then we can access it fro http://$IPADDRESS:8088 in our web browser. Remember to use nohup if yoiu want to detach it from the console

# ./manage.py $IPADDRESS:8088

With the recent release of Ubuntu 9.04 and the brand new X.org stack, finally I have got quick and usable windows effects in my KDE 4.2 install (using Kwin, not Compiz).
My workstation is a Dell Optiplex 745 with an Intel grapphic chipset

$ lspci|grep -i vga
00:02.0 VGA compatible controller: Intel Corporation 82Q963/Q965 Integrated Graphics Controller (rev 02)

with the default install I had serious problems with X, and with serious I mean textures corruptions, artifacts with KDE/Qt4 applications and all sort of graphic glitches.. really a PITA. Then the great idea: Ubuntu 9.04 now ships with a DRI2 enabled kernel, GEM for graphic memory management and this new Intel-sponsored acceleration framework called UXA, which is supposed to improve XAA and EXA. So, if everything is already screwed, why not give it a try?

So I fired up my vim editor and changed my /etc/X11/xorg.conf to look exactly like this, no more no less:

Section "Monitor"
 Identifier      "Configured Monitor"
EndSection

Section "Screen"
        Identifier      "Default Screen"
        Monitor         "Configured Monitor"
        Device          "Configured Video Device"
EndSection

Section "Device"
        Identifier      "Configured Video Device"
        Option          "AccelMethod" "UXA"
EndSection

Section "ServerFlags"
        Option  "DontZap"       "False"
EndSection

restarted X and the magic was done. I activated the composited effects in KWin and everything worked like a charm, really flying as it never did and as it is supposed to do (Vista on the same hardware works the same).
So, if you have a similar hardware, I encourage you to try the same. If anything goes wrong, removing this line

Option "AccelMethod" "UXA"

will fall back the configuration to its default state.

HTH

If you want to disable the nice Message of the Day (MotD) your sysadmin gently shows you evry time you login in your remote shell, then all you have to do is just create a zero-lenght (as in empty) file in your $HOME called .hushlogin

> ~/.hushlogin

(you can use touch as well, or any other mean)
That’s all

Today I stumbled on a discussion here where I work about what’s the best INT field in Mysql to represent boolean values and about what’s the real meaning of the *INT(number) definition.

So, I ended looking in the online Mysql manual for answer but also in the “High Performance MySQL 2nd edition” written by worldwide-fame MySQL hackers (and published by O’Really).

To resume, as Mysql Manual says: BOOLEAN is an alias for TINYINT(1), so you can use both, although BIT could be a better suited solution.

But what about the parenthesis thingie? Here there are two different opinions on the matter. According to High Performance Mysql’s authors (page 82, emphasis’ mine):

MySQL lets you specify a “width” for integer types, such as INT(11). This is meaningless for most applications: it does not restrict the legal range of values, but simply specifies the number of characters MySQL’s interactive tools (such as commandline client) will reserve for display purposes. For storage and computational purposes, INT(1) is identical to INT(20)

but now let’s look at this other page in Mysql Manual (emphasis mine):

When used in conjunction with the optional extension attribute ZEROFILL, the default padding of spaces is replaced with zeros. For example, for a column declared as INT(5) ZEROFILL, a value of 4 is retrieved as 00004. Note that if you store larger values than the display width in an integer column, you may experience problems when MySQL generates temporary tables for some complicated joins, because in these cases MySQL assumes that the data fits into the original column width.

Now…who’s right? I use to trust in the Percona & OpenQuery crew but anyway the official Mysql Manual seems pretty clear about some cases in which the INT(x) value is important.
Any idea?

Sometimes you may in need to use an external SMTP provider to send your emails, and usually ISPs give instruction on how to configure mail clients such as Outlook or Thunderbird. But what if you are already using an internal SMTP server such as Postfix?

These guidelines are for Debian (but may be helpful with other systems as well) and are related to Postfix. The SMTP provider in the example is AuthSMTP which is a well known provider for SMTP relaying.

Given you already have a working Postfix environment, first of all edit your main.cf and add these lines:

relayhost = [mail.authsmtp.com]
smtp_sasl_auth_enable=yes
smtp_sasl_password_maps=hash:/etc/postfix/sasl-passwords
smtp_sasl_mechanism_filter = digest-md5
smtp_sasl_security_options=


then, create with $EDITOR a file called /etc/postfix/sasl-passwords and fill it with something like this:

[mail.authsmtp.com] yourusername:yourpassword

then, compile the map file

# postmap hash:/etc/postfix/sasl-passwords

now we are almost done, just restart postfix and it should work.

Now, probably it won’t really work and you’ll start to see messages like these in your postfix log:

warning: SASL authentication failure: No worthy mechs found
SASL authentication failed; cannot authenticate to server mail.authsmtp.com

that’s because you are missing some SASL packages from Debian. Issue

# aptitude install libsasl2-modules

and it should install all the missing packages and make the thing work :)

Hello,

Maybe you are interested on installing untrusted packages on your Debian box, but by default you are prompted with this prompt:

Do you want to continue? [Y/n/?] y
WARNING: untrusted versions of the following packages will be installed!

Untrusted packages could compromise your system’s security.
You should only proceed with the installation if you are certain that
this is what you want to do.

untrusted_package

Do you want to ignore this warning and proceed anyway?
To continue, enter “Yes”; to abort, enter “No”:

This is fine, since it warns you about it, but it breaks non-interactive scripts, because needs user confirmation.

What then? the solution is easy, you only need to tell to aptitude that you want to use those packages without user confirmation.

From aptitude manual:
Option: Aptitude::CmdLine::Ignore-Trust-Violations
Default: false
Description: In command-line mode, causes aptitude to ignore the installation of untrusted packages. This is a synonym for Apt::Get::AllowUnauthenticated.

Just go!
# aptitude -o Aptitude::Cmdline::ignore-trust-violations=true -y install your_untrusted_package

WARNING: untrusted versions of the following packages will be installed!

Untrusted packages could compromise your system’s security.
You should only proceed with the installation if you are certain that
this is what you want to do.

untrusted_package

*** WARNING *** Ignoring these trust violations because
aptitude::CmdLine::Ignore-Trust-Violations is ‘true’!

Writing extended state information… Done

It does not use an interactive prompt and of course your script will continue :)

See you!

When dealing with bash (or other shells) scripts, instead of starting check outputs, write to temp file, trying to pass variables out of their scope from oine subshell to another, just remember that there is that thing called return status that can do the trick in a simpler, quicker and easier to read way.

For example, if you need to wait for a MySQL server to do not have pending queries before starting to do something, just do


while ( mysqladmin|grep -vi "show processlist"|grep "Query" > /dev/null )
do
sleep 0.1 # or whatever you want, prevent system overload
# ok, it's executing something, let's do thing A
done
# ok, it's done, let's do thing B


It’s (almost) one line long, it’s simple, effective and it just works.

After getting iSCSI working on Debian Etch the next thing to do is to set up multipath to get redundancy in case one path from the SCSI client to the SCSI target fails.

First, let’s digg a bit more in depth about what a path is, what can go wrong and what we can do to prevent it. Usually in a simple iSCSI environment there are two network interfaces dedicated to the remote storage, each one connected to a distinct ethernet switch and each switch connected to the a distinct ethernet interface in the host SAN. Then here you have two separated controller cards (let’s call them A and B) which connect to the same logical volume (a RAID array.. so here redundancy is already covered). I repeat, this is the simplest redundant scenario, in which you can have redundancy, a good fault-tolerance and can parallelize via round-robin the requests from the initiator to the host target.

So, let’s imagine we have configured both interfaces (and all the needed connections) in our server (the initiator) and we send an iSCSI discover request on both interfaces:

:~# iscsiadm -m discovery -t sendtargets -p 172.16.1.10
172.16.1.10:3260,1 iqn.2002-10.com.infortrend:raid.sn7612996.101
:~# iscsiadm -m discovery -t sendtargets -p 172.16.11.10
172.16.11.10:3260,1 iqn.2002-10.com.infortrend:raid.sn7612961.112


as said, both interfaces are connected to the exact same data volume(s), because we want some fault tolerance in case one path fails. But wait… what’s happening in kernel land?

:~# dmesg|grep "SCSI device"| grep -v sda # sda is the local disk
SCSI device sdb: 1638400000 512-byte hdwr sectors (838861 MB)
SCSI device sdb: drive cache: write back
SCSI device sdb: 1638400000 512-byte hdwr sectors (838861 MB)
SCSI device sdb: drive cache: write back
SCSI device sdc: 11717947392 512-byte hdwr sectors (5999589 MB)
SCSI device sdc: drive cache: write back
SCSI device sdc: 11717947392 512-byte hdwr sectors (5999589 MB)
SCSI device sdc: drive cache: write back
SCSI device sdd: 1638400000 512-byte hdwr sectors (838861 MB)
SCSI device sdd: drive cache: write back
SCSI device sdd: 1638400000 512-byte hdwr sectors (838861 MB)
SCSI device sdd: drive cache: write back
SCSI device sde: 11717947392 512-byte hdwr sectors (5999589 MB)
SCSI device sde: drive cache: write back
SCSI device sde: 11717947392 512-byte hdwr sectors (5999589 MB)
SCSI device sde: drive cache: write back


We have two volumes exported from the SAN but our server is detecting four volumes, two pairs of identical volumes to be correct. This is quite normal… we are exporting the same volumes on every path so our initiator detects four distinct volumes. One solution could be to mount sdb and sdc and then, if something goes wrong, manually mount in the same point sdd and sde. But obviously this is something we should avoid because it would create unwanted downtime. So, you need multipath.

In Debian, you can install it with a simple:
aptitude install multipath-tools

and have a very very basic configuration editing /etc/multipath.conf with something like this:


blacklist {
devnode "sda"
}

defaults {
user_friendly_names yes
}


Restart the multipath-tools service and then you’ll get your new devices as /dev/mapper/mpath*. These are absolutely ordinary block devices, so you can partition, format and mount them as they were a normal local disk.
When a path fails, multipathd will automatically exclude it from the dispatching algorithm and you won’t notice the failure happened.

As a final side note, remember that you can use multipath with any number of block devices and they haven’t to be iSCSI devices… it could be a failovered DAS as well, for example (Dell M3000 comes to my mind).

Title says it all. If you want to check (or set) your ethernet NIC configuration or status in Linux, people used to use mii-tools. But there’s a lot more powerful and modern tool that obsoletes it: ethtool
You can install it with your favourite package manager, if it’s not already present in your system.
In Debian/Ubuntu, you can issue
# aptitude install ethtool

Here it is an example:


# ethtool eth0
Settings for eth0:
Supported ports: [ TP ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Half 1000baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Half 1000baseT/Full
Advertised auto-negotiation: Yes
Speed: 100Mb/s
Duplex: Full
Port: Twisted Pair
PHYAD: 1
Transceiver: internal
Auto-negotiation: on
Supports Wake-on: g
Wake-on: d
Current message level: 0x000000ff (255)
Link detected: yes