Posts Tagged ‘Problems’

How to Avoid the 7 Most Frequent Mistakes in Python Programming

Monday, September 9th, 2019

Reading Time: 4minutes


Python is very appealing for Rapid Application Development for many reasons, including high-level built in data structures, dynamic typing and binding, or to use as glue to connect different components. It’s simple and easy to learn but new Python developers can fall in the trap of missing certain subtleties.

Here are 7 common mistakes that are harder to catch but that even more experienced Python developers have fallen for.


1. The misuse of expressions as function argument defaults

Python allows developers to indicate optional function arguments by giving them default values. In most cases, this is a great feature of Python, but it can create some confusion when the default value is mutable. In fact, the common mistake is thinking that the optional argument is set to whatever default value you’ve set every time the function argument is presented without a value. It can seem a bit complicated, but the answer is that the default value for this function argument is only evaluated at the time you’ve defined the function, one time only.  



2. Incorrect use of class variables

Python handles class variables internally as dictionaries and they will follow the Method Resolution Order (MRO). If an attribute is not found in one class it will be looked up in base classes so references to one part of the code are actually references to another part, and that can be quite difficult to handle well in Python. For class attributes, I recommend reading up on this aspect of Python independently to be able to handle them.



3. Incorrect specifications of parameters for exception blocks

There is a common problem in Python when except statements are provided but they don’t take a list of the exceptions specified. The syntax except Exception is used to bind these exception blocks to optional parameters so that there can be further inspections. What happens, however, is that certain exceptions are then not being caught by the except statement, but the exception becomes bound to parameters. The way to get block exceptions in one except statement has to be done by specifying the first parameter as a tuple to contain all the exceptions that you want to catch.


4. Failure to understand the scope rules

The scope resolution on Python is built on the LEGB rule as it’s commonly known, which means Local, Enclosing, Global, Built-in. Although at first glance this seems simple, there are some subtleties about the way it actually works in Python, which creates a more complex Python problem. If you make an assignment to a variable in a scope, Python will assume that variable is local to the scope and will shadow a variable that’s similarly named in other scopes. This is a particular problem especially when using lists.


5. Modifying lists during iterations over it


When a developer deletes an item from a list or array while iterating, they stumble upon a well known Python problem that’s easy to fall into. To address this, Python has incorporated many programming paradigms which can really simplify and streamline code when they’re used properly. Simple code is less likely to fall into the trap of deleting a list item while iterating over it. You can also use list comprehensions to avoid this problem.



6. Name clash with Python standard library


Python has so many library modules which is a bonus of the language, but the problem is that you can inadvertently have a name clash between your module and a module in the standard library. The problem here is that you can accidentally import another library which will import the wrong version. To avoid this, it’s important to be aware of the names in the standard library modules and stay away from using them.



7. Problems with binding variables in closures

Python has a late binding behavior which looks up the values of variables in closure only when the inner function is called. To address this, you may have to take advantage of default arguments to create anonymous functions that will give you the desired behavior – it’s either elegant or a hack depending on how you look at it, but it’s important to know.




Python is very powerful and flexible and it’s a great language for developers, but it’s important to be familiar with the nuances of it to optimize it and avoid these errors.

Ellie Coverdale, a technical writer at Essay roo and UK Writings, is involved in tech research and projects to find new advances and share her insights. She shares what she has learned with her readers on the Boom Essays blog.

Fix Mac OS X camera problems – Tell which application is using Mac OS X builtin Camera

Sunday, September 16th, 2018

Reading Time: 3minutes
It is a common problem on Mac OS X notebooks (MacBook Air , MacBook Proc)  with builtin Video Camera to have issues with Camera in Facetime, Skype and other applications which use it.

Considering that the Camera is physically working on the Mac (it did not burn etc.) and it stooped working suddenly (is not detected by Mac OS applications which support it), the most common cause for that is the fact that another application running on the system is using it.
With the spread of spyware and malware that can easily hit your computer by exploiting Javascript bugs in browser intepreter (Firefox, Chrome, Chrome) it is not impossible that your Mac PC got infected with a kind of WebCam spy software that keeps your Video Camera active all time.

Webcam spying is a real issue of today so to secure yourself partially you can place Oversight App to get notifications when an application starts using Mac's Webcam or audio.

Open Finder and run Terminal to check whether the Web Camera is used by some of the Mac running processes.


Applications -> Utilities -> Terminal






MacBook-Air:Volumes root#  lsof | grep "AppleCamera"


You should see one or more results. If you don’t see any results, try running the following commands as well.
One of the below commands may be necessary if you’re using an older version of macOS.


MacBook-Air:Volumes root#  lsof | grep "iSight"


MacBook-Air:Volumes root#  lsof | grep "VDC"


If VDCAssistant process shows running kill it.

MacBook-Air:Volumes root#  killall -9 VDCAssistant

You can also check whether the Mac Camera is being detected by Mac OS with system_profiler command (this is Mac's equivalent of Linux's lspci / lsusb / lshw / dmidecode for more on the topic you can check my previous article Get hardware system info on Linux etc.)




   Type8Camera::12.781 system_profiler[1075:84585] Exception NSInvalidArgumentE
      Version: 10,1
      Obtained from: Apple
      Last Modified: 13.12.2017, 9:34
      Kind: Intel
      64-Bit (Intel): Yes
      Signed by: Software Signing, Apple Code Signing Certification Authority, Apple Root CA
      Location: /System/Library/Image Capture/Devices/
      Get Info String: 10.1, © Copyright 2002-2014 Apple Inc. All rights reserved.


      Version: 10,1
      Obtained from: Apple
      Last Modified: 13.12.2017, 9:34
      Kind: Intel
      64-Bit (Intel): Yes
      Signed by: Software Signing, Apple Code Signing Certification Authority, Apple Root CA
      Location: /System/Library/Image Capture/Devices/
      Get Info String: 10.1, © Copyright 2001-2014 Apple Inc. All rights reserve



      Version: 10,1
      Obtained from: Apple
      Last Modified: 13.12.2017, 9:34
      Kind: Intel
      64-Bit (Intel): Yes
      Signed by: Software Signing, Apple Code Signing Certification Authority, Apple Root CA
      Location: /System/Library/Image Capture/Devices/
      Get Info String: 10.1, © Copyright 2001-2014 Apple Inc. All rights reserved.


      Version: 10,1
      Obtained from: Apple
      Last Modified: 13.12.2017, 9:34
      Kind: Intel
      64-Bit (Intel): Yes
      Signed by: Software Signing, Apple Code Signing Certification Authority, Apple Root CA

MySQL crashes after upgrade from MySQL to MariaDB and how to fix it

Tuesday, August 21st, 2018

Reading Time: 3minutes


If you have recently upgraded your Debian / Ubuntu / CentOS Linux Server to the latest RPM / DEB packages as part of the upgrade you might have noticed the upgrade of MySQL Community Server  (which was bought by Oracle Corporation few years ago) is automatically upgradedto MariaDB (which is a MySQL fork made by the original developers of MySQL and guaranteed to stay open source. Just to name some of the Notable users include Wikipedia, and Google.).

You might have noticed MariaDB's restart script which is still under /etc/init.d/mysql  won't start and a quick check in /var/log/mysql.err | /var/log/mysql.log
shows errors of /usr/bin/mysqld crashing with errors like:

140502 14:13:05 [Note] Plugin 'FEDERATED' is disabled.
InnoDB: Log scan progressed past the checkpoint lsn 108 1057948207
140502 14:13:06  InnoDB: Database was not shut down normally!
InnoDB: Starting crash recovery.
InnoDB: Reading tablespace information from the .ibd files…
InnoDB: Restoring possible half-written data pages from the doublewrite
InnoDB: buffer…
InnoDB: Doing recovery: scanned up to log sequence number 108 1058059648
InnoDB: 1 transaction(s) which must be rolled back or cleaned up
InnoDB: in total 15 row operations to undo
InnoDB: Trx id counter is 0 562485504
140502 14:13:06  InnoDB: Starting an apply batch of log records to the database…
InnoDB: Progress in percents: 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99
InnoDB: Apply batch completed
InnoDB: Starting in background the rollback of uncommitted transactions
140502 14:13:06  InnoDB: Rolling back trx with id 0 562485192, 15 rows to undo
140502 14:13:06  InnoDB: Started; log sequence number 108 1058059648
140502 14:13:06  InnoDB: Assertion failure in thread 1873206128 in file ../../../storage/innobase/fsp/fsp0fsp.c line 1593
InnoDB: Failing assertion: frag_n_used > 0
InnoDB: We intentionally generate a memory trap.
InnoDB: Submit a detailed bug report to
InnoDB: If you get repeated assertion failures or crashes, even
InnoDB: immediately after the mysqld startup, there may be
InnoDB: corruption in the InnoDB tablespace. Please refer to
InnoDB: about forcing recovery.
140502 14:13:06 – mysqld got signal 6 ;
This could be because you hit a bug. It is also possible that this binary
or one of the libraries it was linked against is corrupt, improperly built,
or misconfigured. This error can also be caused by malfunctioning hardware.
We will try our best to scrape up some info that will hopefully help diagnose
the problem, but since we have already crashed, something is definitely wrong
and this may fail.

It is possible that mysqld could use up to
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 345919 K
bytes of memory
Hope that's ok; if not, decrease some variables in the equation.

thd: 0x0
Attempting backtrace. You can use the following information to find out
where mysqld died. If you see no messages after this, something went
terribly wrong…
stack_bottom = (nil) thread_stack 0x30000
140502 14:13:06 [Note] Event Scheduler: Loaded 0 events
140502 14:13:06 [Note] /usr/sbin/mysqld: ready for connections.
Version: '5.1.41-3ubuntu12.10'  socket: '/var/run/mysqld/mysqld.sock'  port: 3306  (Ubuntu)
/usr/sbin/mysqld(my_print_stacktrace+0x2d) [0xb7579cbd]
/usr/sbin/mysqld(handle_segfault+0x494) [0xb7245854]
/lib/tls/i686/cmov/ [0xb6cc5a82]
/usr/sbin/mysqld(+0x4867e9) [0xb74647e9]
/usr/sbin/mysqld(btr_page_free_low+0x122) [0xb74f1622]
/usr/sbin/mysqld(btr_compress+0x684) [0xb74f4ca4]
/usr/sbin/mysqld(btr_cur_compress_if_useful+0xe7) [0xb74284e7]
/usr/sbin/mysqld(btr_cur_pessimistic_delete+0x332) [0xb7429e72]
/usr/sbin/mysqld(btr_node_ptr_delete+0x82) [0xb74f4012]
/usr/sbin/mysqld(btr_discard_page+0x175) [0xb74f41e5]
/usr/sbin/mysqld(btr_cur_pessimistic_delete+0x3e8) [0xb7429f28]
/usr/sbin/mysqld(+0x526197) [0xb7504197]
/usr/sbin/mysqld(row_undo_ins+0x1b1) [0xb7504771]
/usr/sbin/mysqld(row_undo_step+0x25f) [0xb74c210f]
/usr/sbin/mysqld(que_run_threads+0x58a) [0xb74a31da]

/usr/sbin/mysqld(trx_rollback_or_clean_all_without_sess+0x3e3) [0xb74ded43]
/lib/tls/i686/cmov/ [0xb6f9f96e]
/lib/tls/i686/cmov/ [0xb6d65a4e]
The manual page at contains
information that should help you find out what is causing the crash.

Any recommendations?

I hoped to solve the /usr/bin/mysqldsegfault error with server reboot as I though the problem is caused by the fact libc library was updated, but even a reboot did not solve it.

I've investigated online for a solution and found following MySQL corruption and recovery article.

The solution outlined there is very simple and comes to adding the line:

innodb_force_recovery = 1

to /etc/mysql/my.cnf

Assuming the mysql server is not running before restarting mariadb server.

1. Make a backup (Dump) of all MySQL tables

mysql:~# mysqldump -A > dump.sql

2. Drop all databases which need recovery.
You can do that from mysql cli or phpmyadmin

3. Stop mysqld.

mysql:~# /etc/init.d/mysql restart

4.  Remove /var/lib/mysql/ib*

mysql:~# rm -rf /var/lib/mysql/ib*

5. Comment out innodb_force_recovery in /etc/mysql/my.cnf

6. Restart mysqld. Look at mysql error log.
If everything is fine and you have problems with broken or missing databases the best thing next is to stop again mariadb and

7. Restore databases from the dump

mysql:~# mysql < dump.sql




Fixing Mate Adwaita theme problems on Debian and Ubuntu Linux

Wednesday, October 25th, 2017

Reading Time: 2minutes


After  trying out GNOME 3.2.x enough and giving it enough chance I've decided to finally migrate to Linux Mate graphical environment (the fork of gnome 2 for modern PCs).

I have to say I'm running Debian 9 Stretch on my upgraded Thinkpad R61, after 2 / 3 days upgrade operations from Debian 7 to Debian 8, from Debian 8 to 9.

Just Migrated to Mate all looked fine, but just as I wanted to make the look and feel identical to GNOME 2, I played with Appearance because I wanted to apply theme Adwaita the one, the one so popular since the glorious times when GNOME 2 was a king of the Linux Desktop. 

To add additional themes to MATE, I've installed gnome-themes-standard package, e.g.

apt-get install  --yes gnome-themes-standard

This package provides a number of Themes I could choose from and one of them is Adwaita Not surprisingly, I faced a theme issue
it complains about window manager theme "Adwaita" missing.

Using the example for Adwaita  mate-appearance-properties  gives, I believe this is the "Proper" way to fix it, so do the following in order;

The quick and dirty way when using it

  • Select Adwaita theme
  • Click on Customise


    • Select the Window Border tab
    • Select window border theme "TraditionalOk" and close


A Permanent Fix to the Adwaita missing its Theme Manager using terminal / console

I found that all I had to do to resolve the issue permanently was to do this;

vim /usr/share/themes/Adwaita/index.theme

And change at the bottom where it says 


to say 


instead of  Adwaita .

I know why this works, I just do not know why Adwaita can't use its own Metacity theme without issues, aside from what the kind people at  #gnome @  said about Adwaita previously relying on Mutter.

Feel free to tell me if up explained did not work for you or if you have a better way to deal with the Adwaita missing manager theme issueso far I believe the  problem is resolved correctly.


Testing Qmail installation for problems: Common reasons for unworking qmail / How to debug Qmail mail server failing to delivery or send emails

Friday, November 9th, 2012

Reading Time: 8minutes

Testing qmail installation for problemes finding qmail common component failures

Through my 10 years of experience  in managing and "life with qmail", I've at many times had to deal with suddenly broken or misconducting, qmail installs. With some of them the problems started during new Qmail install configuration time, with others QMAIL worked perfectly for years and then suddenly it stopped working. Nomatter what the situation was, there was a kind of "scenario" and common things to check to debug and find out what is causing the respective qmail installation to not work. In this little, article I will try to share my knowledge in hope that others which configure new QMAIL based mail servers or are in situation to need to recover – "resurrect" a one that suddenly stopped working qmail to its normal operations.

Here are few cases , there are many more, probably hundreds of reasons which might be causing Qmail + Vpopmail  to stop properly delivering e-amails but  as this ones ones are really most likely ones just checking them gives a good clue What is going wrong with  Qmail?.:

  • Something broke up with scheduled daemontools processes;
  • There is no hard disk (the disk is full) and Qmai is unable to writeinside its mail Queue directories (/var/qmail/queue) or Spamassassin or AntiVirus programs fails to write on disk
  • ( /var/qmail/bin/ ) perl script is messed up or if using simscan to do antivirus check-ups instead simscan is failing somewhere
  • something messed up with /var/qmail/control/rcpthosts
  • something messed up with /var/qmail/control/validrcptto.txt or /var/qmail/control/validrcptto.cdb
  •  incorrect main server host in /var/qmail/control/me or /var/qmail/control/plusdomain
  • Messed up vpopmail (virtual domain) records in /var/qmail/control/virtualdomains file
  • problems with insufficient memory (whether there is a softlimit memory limit for /service/qmail-smtpd/run (qmail daemontools start up and monitoring script) – /usr/local/bin/softlimit is no longer proposed used by newer qmail guides but in older ones it was common to appear in /../qmail-smtpd/run
  • Something is wrong with clamd (/usr/sbin/clamd – for example crashed due to bug) or something is wrong with clamav database ( /var/lib/clamav or wherever set to be stored; on some installs /usr/local/lib/clamav) – there most commonly main.cvd and daily.cld break up during freshclam clamav database update.
  • As freshclam takes care for AntiVirus database updates it is good to check it is properly running, either as a service or via a cronjob
  • Assure there are no mistakes or wrong (unexistent) variables in /etc/tcp.smtp file or / and /etc/tcp.smtp.cdb is not broken
  • Permission issues with; qmail main binaries in /var/qmail/bin/ , queue files – /var/qmail/queue or qmail log files /var/log/qmail/…

As I said there are plenty of other possible, reasons but I listed this here, since they're the most common reasons for problems with sent or receive of messages with Qmail mail server.

Checking all of the above and making sure they're okay, I've checked daemontools readprodctitle process as it often signalize for problems with any part of qmail install, there all seemed normal no warnings and errors, e.g.:

qmail:~# ps ax|grep -i -E 'clam|freshclam|spam|vpopmail'
2241 ? Ssl 3:49 /usr/sbin/clamd
2408 ? Ss 11:54 /usr/bin/freshclam -d --quiet
2853 ? S 0:00 tcpserver -H -R -v -c100 0 110 qmail-popup /home/vpopmail/bin/vchkpw qmail-pop3d Maildir
2856 ? S 0:01 tcpserver -vR -l /var/qmail/control/me -c 30 -u 89 -g 89 -x /etc/tcp.smtp.cdb 0 25 rblsmtpd -t0 -r -r -r -r qmail-smtpd /var/qmail/control/me /home/vpopmail/bin/vchkpw /bin/true
2857 ? S 0:00 sslserver -e -vR -l -c 30 -u 89 -g 89 -x /etc/tcp.smtp.cdb 0 465 qmail-smtpd /home/vpopmail/bin/vchkpw /bin/true

qmail:~# ps ax|grep -i qmail
2840 ? S 0:00 supervise qmail-send
2844 ? S 0:00 supervise qmail-smtpd
2846 ? S 0:00 supervise qmail-pop3d
2848 ? S 0:00 supervise qmail-smtpdssl
2850 ? S 0:05 qmail-send
2852 ? S 0:00 multilog t n1024 s1048576 n20 /var/log/qmail/qmail-smtpdssl
2853 ? S 0:00 tcpserver -H -R -v -c100 0 110 qmail-popup /home/vpopmail/bin/vchkpw qmail-pop3d Maildir
2854 ? S 0:00 multilog t s100000 n20 /var/log/qmail/qmail-pop3d
2855 ? S 0:01 multilog t n1024 s1048576 n20 /var/log/qmail/qmail-smtpd
2856 ? S 0:01 tcpserver -vR -l /var/qmail/control/me -c 30 -u 89 -g 89 -x /etc/tcp.smtp.cdb 0 25 rblsmtpd -t0 -r -r -r -r qmail-smtpd /var/qmail/control/me /home/vpopmail/bin/vchkpw /bin/true
2857 ? S 0:00 sslserver -e -vR -l -c 30 -u 89 -g 89 -x /etc/tcp.smtp.cdb 0 465 qmail-smtpd /home/vpopmail/bin/vchkpw /bin/true
2858 ? S 0:01 multilog t n1024 s1048576 n20 /var/log/qmail/qmail-send
2868 ? S 0:01 qmail-lspawn ./Maildir
2869 ? S 0:00 qmail-rspawn
2870 ? S 0:00 qmail-clean
2871 ? S 0:04 qmail-todo
2872 ? S 0:01 qmail-clean
27742 pts/6 S+ 0:00 grep -i qmail

qmail:~# ps ax |grep -i readproc|grep -v grep
48060 ?        S      0:00 readproctitle service errors: ................................................................................................................................................................................................................................................................................................................................................................................................................

As you see  "….." signalize, all is fine with processes scheduled to run over daemontools process. If you instead get warnings or error messages usually the error will point you what is wrong with the qmail install. Common error, I've got over the years here especially on long time functionining qmail installs is insufficient disk space to write in qmail queue and log files.

Also above ps ax|grep -i -E 'clam|freshclam|spam|vpopmail'
shows all 3 clamd, freshclam and vpopmail are up and running so this most likely means all is good with them. Of course sometimes some of those 3 is working and there are problems with the services properly processing emails so it is always a good idea to read qmail log files, in most qmail installations qmail logs are located in /var/log/qmail .

Quickest way is to check all of the qmail related logs in a loop with something like:

qmail:~# for i in $(ls -d /var/log/qmail/*qmail*/); do tail -n 10 $i/current|tai64nlocal; sleep 5; done

Also it is always a good idea to check last 10 lines of clamav, freshclam, qmail-scanner and spamd logs:

qmail:~# tail -n 10 /var/log/qmail/clamav/clamav.log;
Fri Nov 9 06:52:28 2012 -> SelfCheck: Database status OK.
Fri Nov 9 07:52:28 2012 -> SelfCheck: Database status OK.
Fri Nov 9 08:52:28 2012 -> SelfCheck: Database status OK.
Fri Nov 9 09:52:28 2012 -> SelfCheck: Database status OK.
Fri Nov 9 10:52:29 2012 -> SelfCheck: Database status OK.
Fri Nov 9 11:57:29 2012 -> SelfCheck: Database status OK.
Fri Nov 9 12:57:29 2012 -> SelfCheck: Database status OK.
Fri Nov 9 14:14:35 2012 -> SelfCheck: Database status OK.
Fri Nov 9 15:33:46 2012 -> SelfCheck: Database status OK.
Fri Nov 9 16:33:46 2012 -> SelfCheck: Database status OK.

qmail:~# tail -n 10 /var/log/qmail/clamav/freshclam.log
Fri Nov 9 16:20:44 2012 -> --------------------------------------
Fri Nov 9 17:20:44 2012 -> Received signal: wake up
Fri Nov 9 17:20:44 2012 -> ClamAV update process started at Fri Nov 9 17:20:44 2012
Fri Nov 9 17:20:44 2012 -> WARNING: Your ClamAV installation is OUTDATED!
Fri Nov 9 17:20:44 2012 -> WARNING: Local version: 0.97.5 Recommended version: 0.97.6
Fri Nov 9 17:20:44 2012 -> DON'T PANIC! Read
Fri Nov 9 17:20:44 2012 -> main.cvd is up to date (version: 54, sigs: 1044387, f-level: 60, builder: sven)
Fri Nov 9 17:20:44 2012 -> daily.cld is up to date (version: 15557, sigs: 284869, f-level: 63, builder: jesler)
Fri Nov 9 17:20:44 2012 -> bytecode.cld is up to date (version: 191, sigs: 37, f-level: 63, builder: neo)
Fri Nov 9 17:20:46 2012 ->

qmail:~# tail -n 10 /var/log/qmail/qscan/qmail-queue.log
Fri, 09 Nov 2012 13:14:35 EET:14705:
from='', subj='Network Developer', via SMTP from
Fri, 09 Nov 2012 13:14:44 EET:14705: ------ Process 14705 finished. Total of 8.846395 secs
Fri, 09 Nov 2012 15:04:27 EET:21979: +++ starting debugging for process 21979 (ppid=21969) by uid=89
Fri, 09 Nov 2012 15:04:27 EET:21979: g_e_h: return-path='', recips=''
Fri, 09 Nov 2012 15:04:27 EET:21979: from='"G. Georgiev" ', subj='Re: Network Developer', via SMTP from using auth (
Fri, 09 Nov 2012 15:04:34 EET:21979: ------ Process 21979 finished. Total of 6.626484 secs
Fri, 09 Nov 2012 15:33:46 EET:23891: +++ starting debugging for process 23891 (ppid=23884) by uid=89
Fri, 09 Nov 2012 15:33:46 EET:23891: g_e_h: return-path='', recips=''
Fri, 09 Nov 2012 15:33:46 EET:23891: from='"Sandy Richardson" ', subj='RE: Network Developer', via SMTP from

qmail:~# tail -n 10 /var/log/spamd/current |tai64nlocal 2012-11-09 16:25:43.091680500 Nov 9 15:04:27.858 [22049] info: spamd: connection from localhost [] at port 54494
2012-11-09 16:25:43.091683500 Nov 9 15:04:27.948 [22049] info: spamd: checking message <> for qscand:89
2012-11-09 16:25:43.091684500 Nov 9 15:04:33.837 [22049] info: spamd: clean message (0.0/5.0) for qscand:89 in 6.0 seconds, 1104 bytes.
2012-11-09 16:25:43.091690500 Nov 9 15:04:33.838 [22049] info: spamd: result: . 0 - scantime=6.0,size=1104,user=qscand,uid=89,required_score=5.0,rhost=localhost,raddr=,rport=54494,mid=<>,autolearn=ham
2012-11-09 16:25:43.091692500 Nov 9 15:04:34.077 [22043] info: prefork: child states: II
2012-11-09 16:25:43.091692500 Nov 9 15:33:53.626 [22049] info: spamd: connection from localhost [] at port 54681
2012-11-09 16:25:43.091696500 Nov 9 15:33:53.656 [22049] info: spamd: checking message <05e201cdbe7e$d1c83c90$7558b5b0$> for qscand:89
2012-11-09 16:25:43.091697500 Nov 9 15:33:59.467 [22049] info: spamd: clean message (0.0/5.0) for qscand:89 in 5.8 seconds, 33845 bytes.
2012-11-09 16:25:43.091698500 Nov 9 15:33:59.467 [22049] info: spamd: result: . 0 - scantime=5.8,size=33845,user=qscand,uid=89,required_score=5.0,rhost=localhost,raddr=,rport=54681,mid=<05e201cdbe7e$d1c83c90$7558b5b0$>,autolearn=ham
2012-11-09 16:25:43.091702500 Nov 9 15:33:59.506 [22043] info: prefork: child states: II

Whether observing, some of above logs reveals problems to delivery e-mail messages because e-mail boxes are not existing in  /var/qmail/control/validrcptto.cdb – this often happens whether new e-mail boxes are created and the new mail somehow did not enter validrcptto.txt / validrcptto.cdb , you will have to re-build validrcptto.cdb. Rebuilding validrcptto.cdb manually is done with cmd:
br />  

qmail:~# /usr/local/bin/mkvalidrcptto > /var/qmail/control/validrcptto.txt qmail:~# cdbmake-12 /var/qmail/control/validrcptto.cdb /var/qmail/control/validrcptto.tmp < /var/qmail/control/validrcptto.txt

Of course, if the qmail was already properly installed with validrcptto support, this should be done automatically with some cron job set to invoke above commands every 5 minutes or so. In Thibs QmailRocks followed install the script is called /usr/sbin/update-validrcptto and is set to exec every 5 mins.

If spamassassin is configured to automatically update its set of anti-spam rules, via some cron job or smth. it is always a good idea to check if spamassassin, properly loads up does not fail due to some antispam rule:

qmail:~# spamassassin --lint -D ...

You will have to examine carefully, the long returned content for "warning" and "error" keywords. If you don't won't to bother with details you can do, spamassassin –lint

Another good idea whether problems with qmail is of course to rebuild tcpserver cdb file for smtp – this usually solves problems caused by broken /etc/tcp.smtp.cdb.cdb files.

Re-building manually tcp.smtp.cdb is done with:
qmail:~# tcprules /etc/tcp.smtp.cdb /etc/tcp.smtp.tmp < /etc/tcp.smtp
qmail:~# chmod 644 /etc/tcp.smtp.cdb

However, most qmail installation guides recommend or set a qmailctl bash script file, to start / stop / reload / flush qmail queue or simply get status of the qmail installation, so it much easier to rebuild tcp.smtp.cdb through it:
qmail:~# qmailctl cdb
Reloaded /etc/tcp.smtp.

Checking the status of the Qmail Queue state and fixing issues with it can be done using little external tool qmHandle – check my previous article ( Cleaning Qmail filled queue with Spam messages )

To check the basic qmail compontents (qmail-send, qmail-smtpd , qmail-smtpdssl)do:

qmail:~# qmailctl stat
/service/qmail-send: up (pid 2850) 1886193 seconds
/service/qmail-send/log: up (pid 2858) 1886193 seconds
/service/qmail-smtpd: up (pid 2856) 1886193 seconds
/service/qmail-smtpd/log: up (pid 2855) 1886193 seconds
/service/qmail-smtpdssl: up (pid 2857) 1886193 seconds
/service/qmail-smtpdssl/log: up (pid 2852) 1886193 seconds
messages in queue: 2
messages in queue but not yet preprocessed: 0

Another good practice if you have doubts that something is messed with qmail-queue is to check what is waiting to be send in queue:

qmail:~# qmail-qstat
messages in queue: 2
messages in queue but not yet preprocessed: 0

In above paste, from my mail server I have just 2 mails, if you however notice here some large numbers like 5000 or 10000, this might be the cause for asetbacks. If you have plenty of undelivered mails waiting in mail server queue, examine the queue:

qmail:~# qmail-qread ....

Of course it is sometimes, possible to be in situation, where more than one components are creating mail server's sent / receive delivery issues. Anyhow doing a close examination of all possible components usually should (if not reveal what causes the issue) at least give you some pointer to where to search for the problem.

Also for qmail installations based on QmailRocks or Thibs QmailRocksguide, there is a tiny shell script provided, that does evaluation on standard qmail files permissions and binary locations and reports, whether it finds problems with some of them. You can fetch a copy of the qmr_inst_check from here . Although the script is created to check a newly install qmail for problems, it also often helps in determining issues with qmails who mysteriously stopped working.

If you suspect, there are::

Well that's it. Hope this little walk through give you idea where to check on troublesome Qmail install. Please leave a comment if it help you (somehow) solve your issue. Also will be glad to hear if I'm missing somethingi'm sure I am.

Fixing weird problems with missing File Explorer on Polaroid MPCS700 tablet with Andorid 2.2 (Linux kernel 2.6.32)

Wednesday, October 10th, 2012

Reading Time: 2minutesPolaroid MPCs700 Tablet Android version 2.2 with 2.6.32 linux kernel picture

I’ve been given Android Polaroid Tablet which had only 5 clickable icons on main (touchscreen) display:

  • Settings
  • Wi-Fi Settings
  • Youtube
  • Browser
  • App market

The shipped in standard applications for Listening Music, Watching Videos, Managing Photos and Browsing files / ( My Photo, My Video, My Music, File Browser) were missing.

Main problem was File Browser by default shipped with Anroid was missing, and if an USB Stick / Flash Drive is plugged in to the USB port, a message appears along with a sound indicating the USB Flash Drive is detected but there was no way to access the USB Flash drive data ….

The tablet is a second hand bought one and is not my own and it appeared like someone has messed up with it trying to change default Android Linux kernel with some “hacked” (custom compiled one?).

The exact Android version installed on it is 2.2, I checked navigating to:

Settings -> About Device

Android 2.2 Polaroid Settings About Device Screenshot pic

Onwards to fix the messed android I had to reset the device to its factory settings by navigating to:

Settings -> Privacy -> Factory data reset

Android 2.2 Polaroid Settings Privacy Reset to Factory Defaults Screenshot

This formats the device and all installed programs and restores the kernel to its original version, so after few minutes of waiting all worked like a charm 🙂

The normal programs for viewing pics, listening music, File Explorer all come at place. Even both VFAT (Fat 32) and NTFS formatted USB drives file systems worked normally with the device. Before that I was puzzled because I suspected the USB Drive is not detected because the kernel is not supporting NTFS and I need to install something. I was wrong just this Factory data reset and NTFS USB bundled by default works as usual 🙂

Problems with Skype microphone on Thinkpad R61i with Debian Linux again and fix

Tuesday, January 10th, 2012

Reading Time: < 1minute

Once again, I experienced Skype microphone issues!!! Its getting really annoying, since almost randomly I get issues. Skype is a terrible program and depending on a proprietary thing like Skype is a real pain in the ass.
This time it was totally strange as there was no way to record any voice inside Skype Call while testing with (Echo / Sound Test Service)

After a lot of puzzling and getting a bit angry I found this time the issues are caused by some settings which somehow changed in GNOME Sound Preferences microphone to mute:

Sound Preferences GNOME Debian GNU / Linux screenshot

Sound Preferences input gnome Linux muted microphone screenshot

You see on above screeshot that somehow the stupid thing get mutted 😐
GNOME sound preferences unmute mic linux

After unmuting and restarting Skype, the microphone started working in Skype again …

Problems during installation of OpenX on Debian Lenny Linux and their solutions

Tuesday, June 22nd, 2010

Reading Time: 2minutes
If you’re installing openx on a Debian Linux, you will most probably be forced to note/change few things before the openx installation launches correctly:

Here are a list of things to check and assure are properly configured before you procceed1. If you use the disable_functions, it’s recommended to comment it out during the openx installation:
#disable_functions =exec,passthru,shell_exec,system,

2. Increase memory_limit to at least 128MB this is a minimum requirement for openx to run properly:
Edit your /etc/php5/apache2/php.ini and set memory_limit to:
memory_limit = 192M

3. Set the date.timezone in your /etc/php.ini

You need to properly set the date.timezone function in Apache’s php.ini othewise the OpenX installation will refuse to continue with a warning:

timezoneOpenX has detected that your PHP installation is returning ‘System/Localtime’ as the timezone of your server. This is because of a patch to PHP applied by some Linux distributions. Unfortunately, this is not a valid PHP timezone. Please edit your php.ini file and set the ‘date.timezone’ property to the correct value for your server.

It took me a while until I found the proper way to set the date.timezone php variable, below is a correct way to set the date.timezone in php.ini:

echo 'date.timezone = Europe/London' >> /etc/php5/apache2/php.ini

Note that many people has provided a misinformation concerning the setup of date.timezone on php version 5.2 or 5.3.
Many posts online claim that the date.timezone should be set with date.timezone = “Europe/London” having the quotation marks is variable syntax error so if you enter it that way in your php.ini the date.timezone variable won’t be set correctly.
Some people on the net has also suggested that date.timezone variable format is in the form date.timezone = “US/Central” which I suspect is again erroneous.

Actually the Openx system requirements has a nice explanation on how to properly set the date.timezone in order to fix any emerging issues with the OpenX install, so I suggest you take 5 minutes time and read thoroughly before you start with the OpenX installation.

Howto check and isolate problems with DNS servers and Domain records

Monday, March 15th, 2010

Reading Time: < 1minute
There are two handy websites online which helps quite extensively in tracking problems with domain name records and DNS incosistencies.
I used them today to learn more about a problem with a non-resolving DNS though it has already a record in a properly configured Bind nameserver possessing a proper PTR record. Here are three handy online DNS checkers:
1. Squish.Net/DNSCheck – contains Tons of useful debugging information related to the possible problem

2. – provides with less information, though still really handy

Some more handy information realted to DNS can be obtained via R. Scott’s DNS Oversimplified

3. TheDNSReport – provides good and extensive info on problems

Weird Delux 5201 keyboard problems on Linux

Thursday, October 22nd, 2009

Reading Time: < 1minute
I own the shitty Delux 5201 keyboard. On Current Debian Testing/Unstable,a weird keyboard problem occurs. The problem consists in “wsx” keys, refusingto work. It’s really annoying, sometimes all the keyboard keys work, other timesthey don’t … Complete insanity!