Posts Tagged ‘Result’

How to disable spammer domain in QMAIL mail server with badmailto variable

Thursday, July 12th, 2012

Reading Time: < 1 minute

I've recently noticed one of the qmail SMTP servers I adminster had plenty of logged spammer emails originating from yahoo.com.tw destined to reache some random looking like emails (probably unexisting) again to *@yahoo.com.tw

The spam that is tried by the spammer is probably a bounce spam, since it seems there is no web-form or anything wrong with the qmail server that might be causing the spam troubles.
As a result some of the emails from the well configured qmail (holding SPF checks), having a correct existing MX, PTR record and even having configured Domain Keys (DKIM) started being marked, whether emails are sent to *@yahoo.com legit emails.

To deal with the shits, since we don't have any Taiwanese (tw) clients, I dediced to completely prohibit any emails destined to be sent via the mail server to *@yahoo.com.tw. This is done via /var/qmail/control/badmailto qmail control variable;

Here is content of /var/qmail/control/badmailto after banning outgoing emails to yahoo.com.tw;;;

qmail:~# cat /var/qmail/control/badmailto
[!%#:\*\^]
[\(\)]
[\{\}]
@.*@
*@yahoo.com.tw

The first 4 lines are default rules, which are solving a lot of badmailto common sent emails. Thanks God after a qmail restart:

qmail:~# qmailct restart
....

Checking in /var/log/qmail-sent/current, there are no more outgoing *@yahoo.com.tw destined emails. Problem solved …

How road signs evolved / short history of roadsigns

Friday, June 29th, 2012

Reading Time: 2 minutes

how the road signs evolved brief history of road signs Ancient Roman Road of Tall Aqibrin

As a person interested in history and antrophology. Just recently on my last trip to Romania as I travelled a very interesting question poped up in my mind – How it happened that RoadSigns we use on every street highway and practically everywhere on the road came to be. Interestingly now with the standartization of road signs often the most popular road signs are used as a basis for development on other popular prohibit or allowance signs, we read on airports public institutions, pubs and mostly everywhere.

So in short I did a short research on Road Sign History, just to find out once again that the ancients, were wiser than we think. The first road signs probably came to existence with the existence of humanity, however officially, there was no standartization of using signs to point on road locations travellers before it was introudced in the Roman Empire. In Rome a pillars on the roads were placed to point to major road arteries leading to Rome and various important empire city centers.

During the middle ages, milestones pillars were no longer used, but for practical reasons wooden markers placed across european cities instructed tradesman and travellers to major city important centers and were used to show a general road direction leading to nearby city.
The wooden signs practice had been in use until the first modern roadsigns erected  on a wide scale designed for riders of 'high' and ordinary bicycles in the late 1870 and 1880s. The modern road signs as we know it today however emerged as a result of the  first International Road Congress meeting that occured in Rome in 1908.
On the meeting a four standard pictures were selected to note the basic for road signs further development. The need for the meeting was the large increase of roads across european artery cities. The road signs developed on the meeting were bump, curve, intersection and railroad crossings. The invention and adoption of cars and the boom of the car producing industry quickened the need for international road sign standard. The intensive work on international road signs that took place between 1926 and 1949 eventually led to the development of the European road sign system as we know it. The signs were quicky spread to America and in 1960, the road signs become universal in America and almost everywhere all around the developed and developing world.

As of today 2012 it can be said road signs exist all around the civilized world.Though most of road signs are identical across all countries around the world today still some road symbols varies from country to country. I remember seeing some very unique road signs during my travelling through Serbia, 2 years ago.
 

How to disable nginx static requests access.log logging

Monday, March 5th, 2012

Reading Time: 2 minutes

NGINX logo Static Content Serving Stop logging

One of the companies, where I'm employed runs nginx as a CDN (Content Delivery Network) server.
Actually nginx, today has become like a standard for delivering tremendous amounts of static content to clients.
The nginx, server load has recently increased with the number of requests, we have much more site visitors now.
Just recently I've noticed the log files are growing to enormous sizes and in reality this log files are not used at all.
As I've used disabling of web server logging as a way to improve Apache server performance in past time, I thought of implying the same little "trick" to improve the hardware utilization on the nginx server as well.

To disable logging, I proceeded and edit the /usr/local/nginx/conf/nginx.conf file, commenting inside every occurance of:

access_log /usr/local/nginx/logs/access.log main;

to

#access_log /usr/local/nginx/logs/access.log main;

Next, to load the new nginx.conf settings I did a restart:

nginx:~# killall -9 nginx; sleep 1; /etc/init.d/nginx start

I expected, this should be enough to disable completely access.log, browser request logins. Unfortunately /usr/local/nginx/logs/access.log was still displaying growing with:

nginx:~# tail -f /usr/local/nginx/logs/access.log

After a bit thorough reading of nginx.conf config rules, I've noticed there is a config directive:

access_log off;

Therefore to succesfully disable logging I had to edit config occurance of:

access_log /usr/local/nginx/logs/access.log main

to

After a bit thorough reading of nginx.conf config rules, I've noticed there is a config directive:

access_log off;

Therefore to succesfully disable logging I had to edit config occurance of:

access_log /usr/local/nginx/logs/access.log main

to

access_log /usr/local/nginx/logs/access.log main
access_log off;

Finally to load the new settings, which thanksfully this time worked, I did nginx restart:

nginx:~# killall -9 nginx; sleep 1; /etc/init.d/nginx start

And hooray! Thanks God, now nginx logging is disabled!

As a result, as expected the load avarage on the server reduced a bit 🙂

How to reboot remotely Linux server if reboot, shutdown and init commands are not working (/sbin/reboot: Input/output error) – Reboot Linux in emergency using MagicSysRQ kernel sysctl variable

Saturday, July 23rd, 2011

Reading Time: 3 minutesSysRQ an alternative way to restart unrestartable Linux server

I’ve been in a situation today, where one Linux server’s hard drive SCSI driver or the physical drive is starting to break off where in dmesg kernel log, I can see a lot of errors like:

[178071.998440] sd 0:0:0:0: [sda] Result: hostbyte=DID_BAD_TARGET driverbyte=DRIVER_OK,SUGGEST_OK
[178071.998440] end_request: I/O error, dev sda, sector 89615868

I tried a number of things to remount the hdd which was throwing out errors in read only mode, but almost all commands I typed on the server were either shown as missng or returning an error:
Input/output error

Just ot give you an idea what I mean, here is a paste from the shell:

linux-server:/# vim /etc/fstab
-bash: vim: command not found
linux-server:/# vi /etc/fstab
-bash: vi: command not found
linux-server:/# mcedit /etc/fstab
-bash: /usr/bin/mcedit: Input/output error
linux-server:/# fdisk -l
-bash: /sbin/fdisk: Input/output error

After I’ve tried all kind of things to try to diagnose the server and all seemed failing, I thought next a reboot might help as on server boot the filesystems will get checked with fsck and fsck might be able to fix (at least temporary) the mess.

I went on and tried to restart the system, and guess what? I got:

/sbin/reboot init Input/output error

I hoped that at least /sbin/shutdown or /sbin/init commands might work out and since I couldn’t use the reboot command I tried this two as well just to get once again:

linux-server:/# shutdown -r now
bash: /sbin/shutdown: Input/output error
linux-server:/# init 6
bash: /sbin/init: Input/output error

You see now the situation was not pinky, it seemed there was no way to reboot the system …
Moreover the server is located in remote Data Center and I the tech support there is conducting assigned task with the speed of a turtle.
The server had no remote reboot, web front end or anything and thefore I needed desperately a way to be able to restart the machine.

A bit of research on the issue has led me to other people who experienced the /sbin/reboot init Input/output error error mostly caused by servers with failing hard drives as well as due to HDD control driver bugs in the Linux kernel.

As I was looking for another alternative way to reboot my Linux machine in hope this would help. I came across a blog post Rebooting the Magic Wayhttp://www.linuxjournal.com/content/rebooting-magic-way

As it was suggested in Cory’s blog a nice alternative way to restart a Linux machine without using reboot, shutdown or init cmds is through a reboot with the Magic SysRQ key combination

The only condition for the Magic SysRQ key to work is to have enabled the SysRQ – CONFIG_MAGIC_SYSRQ in Kernel compile time.
As of today luckily SysRQ Magic key is compiled and enabled by default in almost all modern day Linux distributions in this numbers Debian, Fedora and their derivative distributions.

To use the sysrq kernel capabilities as a mean to restart the server, it’s necessery first to activate the sysrq through sysctl, like so:

linux-server:~# sysctl -w kernel.sysrq=1
kernel.sysrq = 1

I found enabling the kernel.sysrq = 1 permanently in the kernel is also quite a good idea, to achieve that I used:

echo 'kernel.sysrq = 1' >> /etc/sysctl.conf

Next it’s wise to use the sync command to sync any opened files on the server as well stopping as much of the server active running services (MySQL, Apache etc.).

linux-server:~# sync

Now to reboot the Linux server, I used the /proc Linux virtual filesystem by issuing:

linux-server:~# echo b > /proc/sysrq-trigger

Using the echo b > /proc/sysrq-trigger simulates a keyboard key press which does invoke the Magic SysRQ kernel capabilities and hence instructs the kernel to immediately reboot the system.
However one should be careful with using the sysrq-trigger because it’s not a complete substitute for /sbin/reboot or /sbin/shutdown -r commands.
One major difference between the standard way to reboot via /sbin/reboot is that reboot kills all the running processes on the Linux machine and attempts to unmount all filesystems, before it proceeds to sending the kernel reboot instruction.

Using echo b > /proc/sysrq-trigger, however neither tries to umount mounted filesystems nor tries to kill all processes and sync the filesystem, so on a heavy loaded (SQL data critical) server, its use might create enormous problems and lead to severe data loss!

SO BEWARE be sure you know what you’re doing before you proceed using /proc/sysrq-trigger as a way to reboot ;).