Archive for October, 2011
Sunday, October 30th, 2011 
Have you ever been in need to execute some commands scheduled via a crontab, every let’s say 5 seconds?, naturally this is not possible with crontab, however adding a small shell script to loop and execute a command or commands every 5 seconds and setting it up to execute once in a minute through crontab makes this possible.
Here is an example shell script that does execute commands every 5 seconds:
#!/bin/bash
command1_to_exec='/bin/ls';
command2_to_exec='/bin/pwd';
for i in $(echo 1 2 3 4 5 6 7 8 9 10 11); do
sleep 5;
$command1_to_exec; $command2_to_exec;
done
This script will issue a sleep every 5 seconds and execute the two commands defined as $command1_to_exec and $command2_to_exec
Copy paste the script to a file or fetch exec_every_5_secs_cmds.sh from here
The script can easily be modified to execute on any seconds interval delay, the record to put on cron to use with this script should look something like:
# echo '* * * * * /path/to/exec_every_5_secs_cmds.sh' | crontab -
Where of course /path/to/exec_every_5_secs_cmds.sh needs to be modified to a proper script name and path location.
Another way to do the on a number of seconds program / command schedule without using cron at all is setting up an endless loop to run/refresh via /etc/inittab with a number of predefined commands inside. An example endless loop script to run via inittab would look something like:
while [ 1 ]; do
/bin/ls
sleep 5;
done
To run the above sample never ending script using inittab, one needs to add to the end of inittab, some line like:
mine:234:respawn:/path/to/script_name.sh
A quick way to add the line from consone would be with echo:
echo 'mine:234:respawn:/path/to/script' >> /etc/inittab
Of course the proper paths, should be put in:
Then to load up the newly added inittab line, inittab needs to be reloaded with cmd:
# init q
I've also red, some other methods suggested to run programs on a periodic seconds basis using just cron, what I found in stackoverflow.com's as a thread proposed as a solution is:
* * * * * /foo/bar/your_script
* * * * * sleep 15; /foo/bar/your_script
* * * * * sleep 30; /foo/bar/your_script
* * * * * sleep 45; /foo/bar/your_script
One guy, even suggested a shorted way with cron:
0/15 * * * * * /path/to/my/script
Tags: bashcommand, basis, com, command, command2, copy, copy paste, course, cron, crontab, echo 1, echo echo, endless loop, exec, file, foo, foo bar, freebsd, gnu linux, How to, init, inittab, interval, line, Linux, location, loop, mine, minute, name, nbsp, number, Path, predefined commands, pwd, record, refresh, respawn, run, script, script name, secs, SHA, Shell, shell script, sleep, something, stackoverflow, thread, time, time interval, way
Posted in Linux, Linux and FreeBSD Desktop, System Administration, Various | 1 Comment »
Friday, October 28th, 2011 One of the qmail servers I manage today has started returning strange errors in Squirrel webmail and via POP3/IMAP connections with Thunderbird.
What was rather strange is if the email doesn’t contain a link to a webpage or and attachment, e.g. mail consists of just plain text the mail was sent properly, if not however it failed to sent with an error message of:
Requested action aborted: error in processing Server replied: 451 qq temporary problem (#4.3.0)
After looking up in the logs and some quick search in Google, I come across some online threads reporting that the whole issues are caused by malfunction of the qmail-scanner.pl (script checking mail for viruses).
After a close examination on what is happening I found out /usr/sbin/clamd was not running at all?!
Then I remembered a bit earlier I applied some updates on the server with apt-get update && apt-get upgrade , some of the packages which were updated were exactly clamav-daemon and clamav-freshclam .
Hence, the reason for the error:
451 qq temporary problem (#4.3.0)
was pretty obvious qmail-scanner.pl which is using the clamd daemon to check incoming and outgoing mail for viruses failed to respond, so any mail which contained any content which needed to go through clamd for a check and returned back to qmail-scanner.pl did not make it and therefore qmail returned the weird error message.
Apparently for some reason apparently the earlier update of clamav-daemon failed to properly restart, the init script /etc/init.d/clamav-daemon .
Following fix was very simple all I had to do is launch clamav-daemon again:
linux:~# /etc/inid.d/clamav-daemon restart
Afterwards the error is gone and all mails worked just fine 😉
Tags: action, amp, cause and solution, checking, Clamav, clamd, daemon, email, examination, fine, fix, g mail, google, imap connections, init script, link, logs, mail, online, outgoing mail, pl script, processing, Qmail, qq, reason, Requested, scanner, Search, servers, solution, Squirrel, strange errors, Thunderbird, today, update, usr, Viruses, weird error message
Posted in Linux, Qmail, System Administration | No Comments »
Friday, October 28th, 2011 Every now and then I have to screenshot particular windows positioned on the screen on my GNOME Desktop envronment
Recently I was happy to find there is a very easy way to do this with the default Screenshotting program that is bundled with gnome gnome-screenshot
To screenshot a particular window using gnome-screenshot , its quite easy all one has to do is point the mouse cursor to the window he wants to snapshot and press:
Alt + PrtScr (Print Screen)
Here is a screenshot, I’ve taken of my gnome-terminal using the above command:
One can do it also via the command line using the /usr/bin/gnome-screenshot , by pressing Alt + F2 to invoke the run application and type in:
/usr/bin/gnome-screenshot -w
I was quite happy to find out that this is possible on Linux inside gnome without bothering to run GIMP or use any external programs for the cause. Hope this helps someone 😉
Tags: Alt, application, cause, command, cursor, Desktop, envronment, f2, GIMP, Gnome, gnome desktop, gnu linux, Hope, line, Linux, linux gnome, mouse, mouse cursor, nbsp, Press, Print, PrtScr, run, screen, screenshot, Screenshotting, snapshot, someone, type, usr, usr bin, way
Posted in Linux, Linux and FreeBSD Desktop | No Comments »
Thursday, October 27th, 2011 I just installed munin to track in web the performance of few Debian servers. I’ve configured munin to open via a Virtualhosts in Apache. As its always wise to protect any statistics data about the server from the unwanted possible security violators, I decided to protect Munin with Apache .htaccess.
The munin htmldir output dir is configured to be in /var/www/munin, hence I protected my munin with password by:
1. Creating .htaccess file in /var/www/munin with following content
AuthUserFile /etc/apache2/.munin_htpasswd
AuthGroupFile /dev/null
AuthName EnterPassword
AuthType Basic
require user admin
2. Creating /etc/apache2/.munin_htpasswd with htpasswd (htaccess password generator cmd)
debian:/var/www/munin# htpasswd -c /etc/apache2/.munin_htpasswd admin
New password:
Re-type new password:
Adding password for user admin
Another important thing I had to do is set my VirtualHost file to be configured with AllowOverride All , if AllowOverride All is missing the .htaccess and .htpasswd are not red at all.
Afterwards munin is protected with password, and when my virtualdomain where munin lays e.g. http://munin.mydomain.com is accessed the .htpasswd password dialog pops up 😉
Tags: Allowoverride, apache, apache htaccess, AuthGroupFile, AuthType, AuthUserFile, Creating, data, dev, dialog, dir, EnterPassword, generator, GNU, htaccess password generator, htpasswd, Linux, null, password, performance, pops, security, servers, statistics data, var, Virtualhost, web statistics, www
Posted in Linux, System Administration, Web and CMS | No Comments »
Thursday, October 27th, 2011 
The Ubuntu Linux installed previously on Acer ASPIRE 5736Z on my sisters notebook works quite fine. However today she complained about an issue with her sound. The explanation of the problem she faced is:
When she plays a movie file and pauses it and then switches to a music player, suddenly the notebook sound disappears completely until she restarts all the running programs using the sound server. The Acer Aspire is used with a GNOME Desktop, hence my bet was the issues are most probably caused by some kind of mess happening inside Pulseaudio or the way Alsa loaded kernel drivers handles the multiple sound channel streams.
I’m using GNU / Linux for more than 11 years now and I have faced the same sound issues so many times, so when I heard about the problem I thought its pretty normal.
Anyways, what was really irritating in these situation is that when her laptop sound disappears a video or sound files which are to be played by Mozilla Firefox Browser or Chrome are also loosing the sound.
This causes big issues, especially taking in consideration the fact that she had no idea about computers and is a GUI Desktop user, who have no idea how to restart the pulseaudio server to fix the problem etc.
As a good brother, I took the time to check about the issues related to the specific model of Audio Module Hardware / Sound Card, first I checked the exact model of audio the Acer Aspire 5736Z is equipped with:
stanimiraaaa@Ubuntu-Aspire-5736Z:~$ lspci |grep -i audio
00:1b.0 Audio device: Intel Corporation 82801I (ICH9 Family) HD Audio Controller (rev 03)
I checked about any reported other users issues on the net and I found a user somewhere (lost the link), complaining he is experiencing the same sound oddities on his Acer ASPIRE
The fix he suggested is actually quite simple and comes to adding a simple line to /etc/modprobe.d/alsa-base.conf :
stanimiraaaa@Ubuntu-Aspire-5736Z:~$ sudo su -
[sudo] password for stanimiraaaa:
root@Ubuntu-Aspire-5736Z:~# echo 'options snd_hda_intel model=auto' >> /etc/modprobe.d/alsa-base.conf
Next I restartarted to make the new settings take effect. Its also possible to do it without restart, by unloading and loading the alsa module but I’m a lazy kind of person and the machine is notablyunimportant so why should I bother 😉
One important note here is that I removed also an .asoundrc file, that I created some long time ago and this file might have been creating also some sound issues, the content of ~/.asoundrc, before I delete it in her home user, was like so:
stanimiraaaa@Ubuntu-Aspire-5736Z:~$ cat ~/.asoundrc
pcm.!default {
type hw
card 1
device 0
}
ctl.!default {type hw
card 1
device 0
}
stanimiraaaa@Ubuntu-Aspire-5736Z:~$ rm -f .asoundrc
Doing this minor changes to the Ubuntu system erradicated the sound problems and now the sound with simultaneous sound channel streams works just perfect! Thx God 😉
Tags: alsa, asoundrc, audio controller, bet, card, Chrome, consideration, Desktop, desktop user, exact model, explanation, file, firefox browser, Gnome, gnome desktop, gnu linux, hardware sound, hd, instance, intel corporation, kernel drivers, laptop, mess, modprobe, Module, movie file, Mozilla, music player, music streams, notebook, oddities, player, running programs, sound card, sound files, sound server, sudo, time, type, video
Posted in Everyday Life, Linux, Linux Audio & Video, Various | 2 Comments »
Wednesday, October 26th, 2011 
Yesterday night, one more Computer Genius – John McCarthy has passed away at the age of 84.
John McCarthy is mostly famous for the creation of Lisp Programming language, which was probably the most used programming language in the short past. There are plenty of corporate old iron hardwares which still run programs written in Lisp. Lisp is the language in which Richard Stallman has created his so famous EMACS text editor for GNU.
Computer Technology students, should have studied certainly Lisp in the form of Lisp Scheme.
Lisp is the the second oldest high level programming language only to be predeceded by Fortran .
Lisp gave birth to the so called Macro programming languages
and was invented by McCarthy in 1958, while he was in Massachusetts MIT university.
What is so important about Lisp is that it is de-facto the first language in the world which was written to be suitable for AI (Artificial Intelligence) researches. There is plenty of interesting information about Lisp as well as a number of forks and variations circulating for almost all the existing major operating systems nowdays.
Besides LISP creation McCarthy was in the first team who did a the first Remote Computer Chess game. The game played was among USSR and US scientists, where the moves were transferred by telegraph.
In 1972 MCCarthy was awarded with the Turing Award – (Today probably the most prestigious award for incredible technology achievements in the world).
McCarth’s home website had a lot of great papers on programming languages, mathematical theory of computation and most importantly philosophical words and notes on Artificial Intelligence
His site has a lot of his essays as well as his personal views on the world and predictions (foreseen probabilities by him) on the world future.
McCarthy had even written a short Sci-Fi story (The Robot and The Baby), the story aim was to explore the question, whether robots should have simulated emotions.
John McCarthy is among the brightest computer genius who ever live on this planet as well as a true “icon” for a computer hacker. The news for his death is quite shocking especially after the sudden death of the creator of C programming Language and UNIX Denis Ritchie , and a week earlier the pass of Steve Jobs
It seems like no coincidence, that the brightest computer minds are departuring this life, probably God is taking them one by one just like he gave them the gifts to invent and revolutionize the technology we use today.
Surely McCarthy has left a huge landmark on technology and his name will be in the books for the generations to come.
Tags: age, aim, artificial intelligence, award, birth, chess game, Computer, computer chess, computer genius, computer technology students, death, editor, emacs text editor, Father, form, GNU, information, Intelligence, iron hardwares, john mccarthy, level, level programming language, macro programming, mathematical theory of computation, mit university, number, old iron, operating, planet, programming language creator, programming languages, quot, Remote, remote computer, richard stallman, Robot, sci fi story, story, team, technology achievements, text, theory of computation, Turing, turing award
Posted in Everyday Life, Programming, Various | 1 Comment »
Wednesday, October 26th, 2011 
After configuring a new Qmail+POP3+IMAP with vpopmail install based on Thibs QmailRocks I faced some issues with configuring mail accounts in Mozilla Thunderbird. The problem is also present in Microsoft Outlook Express as some colleagues working on Windows reported they can't configure there email accounts in Outlook either.
The issue was like this, the mail server is running fine, and I can send without issues directly from the server shell with mail command, however in Thunderbird I could only fetch the messages via POP3 or IMAP, whever I give a try to send one I got the error:
Sending of Message Failed
The message could not be sent using SMTP server for an
unknown reason. Please verify that SMTP server settings are correct and try
again, or contact your network administrator
Here is a screenshot preseting the issue, taken from my Thunderbird:
The reason for this error is an automatic setting that is being configured in Thunderbird in New Account Creation time:
Thunderbird queries the mail server and asks for the type of encryptions available for both POP3 and SMTP MX primary host.
Seeing that it supports STARTTLS data transfer encryption mail protocol for both POP3 / IMAP, Thunderbirds auto configuration does place STARTTLS to be used with SMTP and POP3
The incorrect setting which is being automatically filled in can be checked in following these Thunderbird menus:
Edit -> Account Settings -> Outgoing Server (SMTP)
If the configured mail account MX server is let's say mail.exampledomain.com one needs to Edit the settings for this SMTP auto configured domains and he will see some example settings like the one shown in the below screenshot:
You can see from above's screenshot that the auto configured Connection Security setting is improperly set to: STARTTLS. Usually STARTTLS should be working on SMTP port 25, however it seems the problem consists in the fact that the MAIL FROM and RCPT TO is sent in incorrec time (ain't sure if its before or after the encryption).
Therefore the consequence of this failure to use STARTTLS being detected as the correct encryption type for SMTP lead that the new configured mail server clients were unable tot properly connect and send emails via the SMTP listening server on port 25.
I give a try and changing the Connection Security:STARTTLS to Connection SecuritySSL/TLS immediately resolved the SMTP sending issues. Therefore as I found out the SMTP server is working just fine configured to use my QMAIL on port 465 with Connection Security: SSL/TLS and hence to work around the SMTP sending issues, decided to completely disable the STARTTLS encryption to be reported as a supported encryption by qmail-smtpd
On Thibs QmailRocks and some other Qmail installstions based more or less on qmail.jms1.net service damemontools scripts, this can be done by simply changing a line:
DENY_TLS=0
to
DENY_TLS=1
The qmail start up scripts which these change has to be done if one has configured a mail server based on QmailRocks Thibs updated tutorial are:
1. /service/qmail-smtpd
2. /service/qmail-smtpdssl
A quick way to do the DENY_TLS=0 to DENY_TLS=1 changes via sed is like this:
qmail# sed -e 's#DENY_TLS=0#DENY_TLS=1#g' /service/qmail-smtpd/run >> /tmp/qmail-smtpd-run;qmail# sed -e 's#DENY_TLS=0#DENY_TLS=1#g' /service/qmail-smtpdssl/run >> /tmp/qmail-smtpdssl-run;qmail# mv /tmp/qmail-smtpd-run /service/qmail-smtpd/run
qmail# mv /tmp/qmail-smtpdssl-run /service/qmail-smtpdssl/run
After the correct modifications, of course as usual a qmail restart is required, e.g.:
qmail# qmailctl restart
...
Making this changes, irradicated the sending issues. It's best practice that the account which had issues with sending before is deleted and recreated from scratch.
Hope this helps somebody out there who encounters the same issue. Cheers 😉
Tags: account creation, account settings, administratorHere, anunknown, auto configuration, com, configure, configured, connection security, creation time, email accounts, encryption, Express, host, How to, inco, issue, mail account, mail accounts, mail command, mail protocol, mail server, Microsoft, microsoft outlook express, Mozilla, mozilla thunderbird, mx server, network administrator, Outgoing, outgoing server, outlook, outlook mail, place, pop, Qmail, QmailRocks, reason, screenshot, Sending, server settings, server smtp, Shell, smtp, smtp port 25, starttls, thunderbirds, time, TLS, tmp, type, working
Posted in FreeBSD, Linux, Qmail, System Administration, Various, Web and CMS | 5 Comments »
Tuesday, October 25th, 2011 I needed to add a newly created MySQL user with no access to any database with no special permissions (user is created from phpmyadmin) with some permissions to a specific database which is used for the operation of a website, here are the MySQL CLI client commands I issued to make it work:
# mysql -u root -p
mysql> GRANT ALL ON Sql_User_DB.* TO Sql_User@localhost;
mysql> FLUSH PRIVILEGES;
Where in the Example Sql_User_DB is my example database to which the user is granted access and my sample user is Sql_User .
Note that without FLUSH PRIVILEGES; new privileges might not be active.
To test further if all is fine login with Sql_User and try to list database tables.
$ mysql -u Sql_User -p
password:
mysql> USE Sql_User_DB;
mysql> SHOW TABLES;
...
Tags: cli, client, Database, Delete, example, example database, FLUSH, Insert, localhost, Mysql, operation, phpmyadmin, Privileges, root, sample, SQL, TABLE, table permissions, update, User, website
Posted in Linux, MySQL, System Administration, Various, Web and CMS | No Comments »
Tuesday, October 25th, 2011 
After a recent new Debian Squeeze Apache+PHP server install and moving a website from another server host running on CentOS 5.7 Linux server, some of the PHP scripts running via crontab started displaying the following annoying PHP Warnings :
debian:~# php /home/website/www/cron/update.php
PHP Warning: PHP Startup: Unable to load dynamic library '/usr/lib/php5/20090626/suhosin.so' – /usr/lib/php5/20090626/suhosin.so: cannot open shared object file: No such file or directory in Unknown on line 0
Obviously the error revealed that PHP cli is not happy that, I've previously removes the suhosin php5-suhosin module from the system.
I wouldn't have removed php5-suhosin if sometimes it doesn't produced some odd experiences with the Apache webserver.
To fix the PHP Warning, I used first grep to see, where exactly the suhosin module gets included in debian's php.ini config files.
debian:~# cd /etc/php5
debian:/etc/php5# grep -rli suhosin *
apache2/conf.d/suhosin.ini
cgi/conf.d/suhosin.ini
cli/conf.d/suhosin.ini
conf.d/suhosin.ini
Yeah that's right Debian has three php.ini php config files. One for the php cli – /usr/bin/php, another for the Apache webserver loaded php library – /usr/lib/apache2/modules/libphp5.so and one for Apache's cgi module – /usr/lib/apache2/modules/mod_fcgid.so .
I was too lazy to edit all the above found declarations trying to include the suhosin module in PHP, hence I remembered that probably all this obsolete suhosin module declaration are still present because probably the php5-suhosin package is still not purged from the system.
A quick check with dpkg , further strenthened my assumption as the php5-suhosin module was still hanging around as an (rc – remove candidate);
debian:~# dpkg -l |grep -i suhosin
rc php5-suhosin 0.9.32.1-1 advanced protection module for php5
Hence to remove the obsolete package config and directories completely out of the system and hence solve the PHP Warning I used dpkg –purge, like so:
debian:~# dpkg --purge php5-suhosin
(Reading database ... 76048 files and directories currently installed.)
Removing php5-suhosin ...
Purging configuration files for php5-suhosin ...
Processing triggers for libapache2-mod-php5 ...
Reloading web server config: apache2.
Further on to make sure the PHP Warning is solved I did the cron php script another go and it produced no longer errors:
debian:~# php /home/website/www/cron/update.php
debian:~#
Tags: apache, apache php, assumption, candidate, CentOS, cgi, cgi module, cli, config, cron, debian gnu, declaration, declarations, doesn, dpkg, file, gnu linux, host, ini, inicgi, iniconf, lib, libapache, Linux, mod, odd experiences, package, php scripts, php server, protection, right, rli, server host, shared object, squeeze, suhosin, unable to load dynamic library, Warnings
Posted in Linux, System Administration, Various, Web and CMS | 8 Comments »
Monday, October 24th, 2011 I needed to link a new created WordPress Post to external web page address. So when one clicks over the created post he opens an external website.
I’ve googled around to see how this can be achieved and found ordpress external links plugin
I gave a go of the plugin, but pitily I couldn’t make it work. I decided to try some other methods and after some time I tried another approach. I used the HTML >a href=””< My Post Title </a> as a title and it appeared this simple method prooved working 😉
Here is a small screenshot, from wordpress Add New Post dialog
By the way the information online I’ve found on how this the external link creation for a Page or a Post is made was quite obscure and messy. i wonder why there is no clear explanation on the direct a href link creation, especially since WordPress is a de-facto standard for a blogging platform and nowdays powers up so many websites engines around the world.
Tags: creation, de facto standard, dialog, external url, external web, href, href link, HTML, information, link, link creation, lt, nowdays, online, page, platform, plugin, post, quot, screenshot, standard, time, url, way, web page address, Wonder, Wordpress, working
Posted in Linux, Various, Web and CMS, Wordpress | 3 Comments »
