SCAM

Τον τελευταίο καιρό, όλο και περισσότερα email με το παρακάτω (ή παρόμοιο) body φτάνουν στο mailbox μου.
Οι περισσότεροι από εσάς, εύκολα θα διαπιστώσετε πως το παρακάτω είναι google translate, άλλοι πάλι όχι με μια πρώτη ματιά.

Be careful

Είναι, λοιπόν, ένα SCAM email, που προσπαθεί να σας ψαρέψει τα στοιχεία.

Π Ο Τ Ε καμία εταιρεία (πάροχος ή τράπεζα) δεν πρόκειται να σας ζητήσει μέσω email τα στοιχεία σας.

για αυτό Μ Η Ν απαντάτε ΠΟΤΕ σε emails της παρακάτω μορφής.

Actions

Το καλύτερο που έχετε να κάνετε, είναι να προωθήσετε ΑΜΕΣΩΣ το παρακάτω email στο abuse department της εταιρείας σας.

Μπορείτε να βοηθήσετε στην καταπολέμηση της εξάπλωσης αυτού του scam.

Abuse

Τα εκάστοτε abuse departments έχουν εργαλεία που καταγράφουν αυτές τις απόπειρες “ψαρέματος” κι εντοπίζουν τα μολυσμένα PC ή compromised accounts

Με ένα γρήγορο online search βρίσκουμε πολύ γρήγορα μερικά από τα παρακάτω abuse email addresses:

abuse@cosmote.gr
abuse@ote.gr
abuse@forthnet.gr
abuse@wind.gr
abuse@hq.cyta.gr
abuse@hol.gr
postmaster@hol.gr
abuse@nbg.gr
abuse@alpha.gr
support@winbank.gr

Inform Other People

Το καλύτερο που έχετε να κάνετε, είναι να μιλήσετε με τους ανθρώπους του κύκλου σας και να τους ενημερώσετε σχετικά με αυτό.
Μην ξεχνάτε πως εάν τους “χακέψουν” πολύ πιθανά να έχουν στους υπολογιστές τους, δικά σας στοιχεία (από την αποθηκευμένη ατζέντα επαφών)
ή (μερική) πρόσβαση στα email που τους έχετε στείλει κι εσείς.

Οπότε, προστατεύοντάς τους, προστατεύεται και τον εαυτό σας!!

Body

παρακάτω, ένα ενδεικτικό δείγμα. Μπορεί το κείμενο να δείχνει σε άλλο πάροχο ή σε κάποια τράπεζα.
Να έχει κάποιο σύνδεσμο, στον οποίο να πρέπει να πατήσει κάποιος και να συμπληρώσει τα στοιχεία του
ή κάποια φόρμα επικοινωνίας.

Μην ξεχνάτε: Π Ο Τ Ε δεν πρέπει να δίνουμε τα στοιχεία μας, όταν βλέπουμε τέτοια emails.

Cosmote υπηρεσία OTEnet Mail

Μετά την αυτόματη ανανέωση της εγγραφή® σας το διακομιστής αντιμετώπισε κάποια λάθη να μην απαριθμήσω διεύθυνση σας.
Σας ενημερώνουμε ότι δεν μπορείτε να αποκτήσετε πρόσβαση στο λογαριασμό σας! Ή χρησιμοποιήστε το σχετικό προφίλ
αν δεν αναγνωρίσετε τον εαυτό σας σύμφωνα με τους κανονισμούς μας. Παρακαλώ μέσα σε 72 ώρες για να επιβεβαιώσετε
τη διεύθυνση ηλεκτρονικού ταχυδρομείου σας OTEnet Mail, καθώς και όλες τις πληροφορίες που ζητούνται μέσω της παρακάτω φόρμας.

ΕΠΙΒΕΒΑΙΩΣΗ ΤΟΥ ΕΝΤΥΠΟΥ (κάντε κλικ απάντηση και διαβιβάζει τα στοιχεία σας στην υπηρεσία επιβεβαίωσης στη συνέχεια αποστολή)

όνομα:........................
Όνομα:........................
Στοιχεία σύνδεσης (Απαιτείται)
Email OTEnet! :........................
κωδικό πρόσβασης:........................
Εναλλακτικές Email:........................
κωδικό πρόσβασης:........................
χώρα:........................
Ταχυδρομικός κώδικας:........................
τηλέφωνο:........................

Σημείωση: Σε περίπτωση έλλειψης των πληροφοριών που ζητούνται γνωρίζετε ότι αυτό θα διαγράψει οριστικά τη διεύθυνση ηλεκτρονικού ταχυδρομείου σας.

Με εκτίμηση.

Let’s Encrypt

I’ve written some posts on Let’s Encrypt but the most frequently question is how to auto renew a certificate every 90 days.

Disclaimer

This is my mini how-to, on centos 6 with a custom compiled Python 2.7.13 that I like to run on virtualenv from latest git updated certbot. Not a copy/paste solution for everyone!

Cron

Cron doesnt not seem to have something useful to use on comparison to 90 days:

Modification Time

The most obvious answer is to look on the modification time on lets encrypt directory :

eg. domain: balaskas.gr

# find /etc/letsencrypt/live/balaskas.gr -type d -mtime +90 -exec ls -ld {} \;

# find /etc/letsencrypt/live/balaskas.gr -type d -mtime +80 -exec ls -ld {} \;

# find /etc/letsencrypt/live/balaskas.gr -type d -mtime +70 -exec ls -ld {} \;

# find /etc/letsencrypt/live/balaskas.gr -type d -mtime +60 -exec ls -ld {} \;

drwxr-xr-x. 2 root root 4096 May 15 20:45 /etc/letsencrypt/live/balaskas.gr

OpenSSL

# openssl x509 -in <(openssl s_client -connect balaskas.gr:443 2>/dev/null) -noout -enddate

Email

If you have registered your email with Let’s Encrypt then you get your first email in 60 days!

Renewal

Here are my own custom steps:

#  cd /root/certbot.git
#  git pull origin 

#  source venv/bin/activate && source venv/bin/activate
#  cd venv/bin/

#  monit stop httpd 

#  ./venv/bin/certbot renew --cert-name balaskas.gr --standalone 

#  monit start httpd 

#  deactivate

Script

I use monit, you can edit the script accordingly to your needs :

#!/bin/sh

DOMAIN=$1

## Update certbot
cd /root/certbot.git
git pull origin 

# Enable Virtual Environment for python
source venv/bin/activate && source venv/bin/activate 

## Stop Apache
monit stop httpd 

sleep 5

## Renewal
./venv/bin/certbot renew  --cert-name ${DOMAIN} --standalone 

## Exit virtualenv
deactivate 

## Start Apache
monit start httpd

All Together

# find /etc/letsencrypt/live/balaskas.gr -type d -mtime +80 -exec /usr/local/bin/certbot.autorenewal.sh balaskas.gr \;

Systemd Timers

or put it on cron

whatever :P

How to install slack dekstop to archlinux

Download Slack Desktop

eg. latest version

https://downloads.slack-edge.com/linux_releases/slack-2.6.3-0.1.fc21.x86_64.rpm

Extract under root filesystem

# cd /

# rpmextract.sh slack-2.6.3-0.1.fc21.x86_64.rpm

Done

Actually, that’s it!

Run

Run slack-desktop as a regular user:

$ /usr/lib/slack/slack

Slack Desktop

Proxy

Define your proxy settings on your environment:

declare -x ftp_proxy="proxy.example.org:8080"
declare -x http_proxy="proxy.example.org:8080"
declare -x https_proxy="proxy.example.org:8080"

Slack

Iterator

a few months ago, I wrote an article on RecursiveDirectoryIterator, you can find the article here: PHP Recursive Directory File Listing . If you run the code example, you ‘ll see that the output is not sorted.

Object

Recursive Iterator is actually an object, a special object that we can perform iterations on sequence (collection) of data. So it is a little difficult to sort them using known php functions. Let me give you an example:

$Iterator = new RecursiveDirectoryIterator('./');
foreach ($Iterator as $file)
    var_dump($file);

object(SplFileInfo)#7 (2) {
  ["pathName":"SplFileInfo":private]=>
  string(12) "./index.html"
  ["fileName":"SplFileInfo":private]=>
  string(10) "index.html"
}

You see here, the iterator is an object of SplFileInfo class.

Internet Answers

Unfortunately stackoverflow and other related online results provide the most complicated answers on this matter. Of course this is not stackoverflow’s error, and it is really a not easy subject to discuss or understand, but personally I dont get the extra fuzz (complexity) on some of the responses.

Back to basics

So let us go back a few steps and understand what an iterator really is. An iterator is an object that we can iterate! That means we can use a loop to walk through the data of an iterator. Reading the above output you can get (hopefully) a better idea.

We can also loop the Iterator as a simply array.

eg.

$It = new RecursiveDirectoryIterator('./');
foreach ($It as $key=>$val)
    echo $key.":".$val."n";

output:

./index.html:./index.html

Arrays

It is difficult to sort Iterators, but it is really easy to sort arrays!
We just need to convert the Iterator into an Array:

// Copy the iterator into an array
$array = iterator_to_array($Iterator);

that’s it!

Sorting

For my needs I need to reverse sort the array by key (filename on a recursive directory), so my sorting looks like:

krsort( $array );

easy, right?

Just remember that you can use ksort before the array is already be defined. You need to take two steps, and that is ok.

Convert to Iterator

After sorting, we need to change back an iterator object format:

// Convert Array to an Iterator
$Iterator = new ArrayIterator($array);

and that’s it !

Full Code Example

the entire code in one paragraph:

<?php
# ebal, Fri, 07 Jul 2017 22:01:48 +0300

// Directory to Recursive search
$dir = "/tmp/";

// Iterator Object
$files =  new RecursiveIteratorIterator(
          new RecursiveDirectoryIterator($dir)
          );

// Convert to Array
$Array = iterator_to_array ( $files );
// Reverse Sort by key the array
krsort ( $Array );
// Convert to Iterator
$files = new ArrayIterator( $Array );

// Print the file name
foreach($files as $name => $object)
    echo "$namen";

?>

Prologue

Part of my day job is to protect a large mail infrastructure. That means that on a daily basis we are fighting SPAM and try to protect our customers for any suspicious/malicious mail traffic. This is not an easy job. Actually globally is not a easy job. But we are trying and trying hard.

ReplyTo

The last couple months, I have started a project on gitlab gathering the malicious ReplyTo from already identified spam emails. I was looking for a pattern or something that I can feed our antispam engines with so that we can identify spam more accurately. It’s doesnt seem to work as i thought. Spammers can alter their ReplyTo in a matter of minutes!

TheList

Here is the list for the last couple months: ReplyTo
I will -from time to time- try to update it and hopefully someone can find it useful

Free domains

It’s not much yet, but even with this small sample you can see that ~ 50% of phishing goes back to gmail !

    105 gmail.com
     49 yahoo.com
     18 hotmail.com
     17 outlook.com

More Info

You can contact me with various ways if you are interested in more details.

Preferably via encrypted email: PGP: ‘ 0×1c8968af8d2c621f ‘
or via DM in twitter: @ebalaskas

PS

I also keep another list, of suspicious fwds
but keep in mind that it might have some false positives.

Prologue

I should have written this post like a decade ago, but laziness got the better of me.

I use TLS with IMAP and SMTP mail server. That means I encrypt the connection by protocol against the mail server and not by port (ssl Vs tls). Although I do not accept any authentication before STARTTLS command is being provided (that means no cleartext passwords in authentication), I was leaving the PLAIN TEXT authentication mechanism in the configuration. That’s not an actual problem unless you are already on the server and you are trying to connect on localhost but I can do better.

LDAP

I use OpenLDAP as my backend authentication database. Before all, the ldap attribute password must be changed from cleartext to CRAM-MD5

Typing the doveadm command from dovecot with the password method:

# doveadm pw

Enter new password:    test
Retype new password:   test
{CRAM-MD5}e02d374fde0dc75a17a557039a3a5338c7743304777dccd376f332bee68d2cf6

will return the CRAM-MD5 hash of our password (test)

Then we need to edit our DN (distinguished name) with ldapvi:

From:

uid=USERNAME,ou=People,dc=example,dc=org
userPassword: test

To:

uid=USERNAME,ou=People,dc=example,dc=org
userPassword: {CRAM-MD5}e02d374fde0dc75a17a557039a3a5338c7743304777dccd376f332bee68d2cf6

Dovecot

Dovecot is not only the imap server but also the “Simple Authentication and Security Layer” aka SASL service. That means that imap & smtp are speaking with dovecot for authentication and dovecot uses ldap as the backend. To change AUTH=PLAIN to cram-md5 we need to do the below change:

file: 10-auth.conf

From:

auth_mechanisms = plain

To:

auth_mechanisms = cram-md5

Before restarting dovecot, we need to make one more change. This step took me a couple hours to figure it out! On our dovecot-ldap.conf.ext configuration file, we need to tell dovecot NOT to bind to ldap for authentication but let dovecot to handle the authentication process itself:

From:

# Enable Authentication Binds
# auth_bind = yes

To:

# Enable Authentication Binds
auth_bind = no

To guarantee that the entire connection is protected by TLS encryption, change in 10-ssl.conf the below setting:

From:

ssl = yes

To:

ssl = required

SSL/TLS is always required, even if non-plaintext authentication mechanisms are used. Any attempt to authenticate before SSL/TLS is enabled will cause an authentication failure.

After that, restart your dovecot instance.

Testing

# telnet example.org imap

Trying 172.12.13.14 ...
Connected to example.org.
Escape character is '^]'.
* OK [CAPABILITY IMAP4rev1 LITERAL+ SASL-IR LOGIN-REFERRALS ID ENABLE IDLE STARTTLS AUTH=CRAM-MD5] Dovecot ready.

1 LOGIN USERNAME@example.org test

1 NO [ALERT] Unsupported authentication mechanism.
^]
telnet> clo

That meas no cleartext authentication is permitted

MUA

Now the hard part, the mail clients:

RainLoop

My default webmail client since v1.10.1.123 supports CRAM-MD5
To verify that, open your application.ini file under your data folder and search for something like that:

    imap_use_auth_plain = On
    imap_use_auth_cram_md5 = On
    smtp_use_auth_plain = On
    smtp_use_auth_cram_md5 = On

as a bonus, rainloop supports STARTTLS and authentication for imap & smtp, even when talking to 127.0.0.1

Thunderbird

K9

This is my basic home setup for a nice cup of coffee:

You can find my posts regarding coffee here: coffee

I’ve tried to clean up my graef coffee grinder with a small cup of instant rice.
and the results are pretty good:

(click on images for more detail)

When traveling, I make an effort to visit the local hackerspace. I understand that this is not normal behavior for many people, but for us (free / opensource advocates) is always a must.

This was my 4th week on Bratislava and for the first time, I had a couple free hours to visit ProgressBar HackerSpace.

For now, they are allocated in the middle of the historical city on the 2nd floor. The entrance is on a covered walkway (gallery) between two buildings. There is a bell to ring and automated (when members are already inside) the door is wide open for any visitor. No need to wait or explain why you are there!

Entering ProgressBar there is no doubt that you are entering a hackerspace.

You can view a few photos by clicking here: ProgressBar - Photos

And you can find ProgressBar on OpenStreet Map

Some cool-notable projects:

• bitcoin vending machine
• robot arm to fetch clubmate
• magic wood to switch on/off lights
• blinkwall
• Cool T-shirts

their lab is fool with almost anything you need to play/hack with.

I was really glad to make time and visit them.

An Amazing Book!!!

Must Read !!

I’ve listened to the audiobook like in two days.
Couldnt leave it down.

Then organize a CryptoParty to your local hackerspace

Failures

Every SysAdmin, DevOp, SRE, Computer Engineer or even Developer knows that failures WILL occur. So you need to plan with that constant in mind. Failure causes can be present in hardware, power, operating system, networking, memory or even bugs in software. We often call them system failures but it is possible that a Human can be also the cause of such failure!

Listening to the stories on the latest episode of stack overflow podcast felt compelled to share my own oh-shit moment in recent history.

I am writing this article so others can learn from this story, as I did in the process.

Rolling upgrades

I am a really big fun of rolling upgrades.

I am used to work with server farms. In a nutshell that means a lot of servers connected to their own switch behind routers/load balancers. This architecture gives me a great opportunity when it is time to perform operations, like scheduling service updates in working hours.

eg. Update software version 1.2.3 to 1.2.4 on serverfarm001

The procedure is really easy:

• From the load balancers, stop any new incoming traffic to one of the servers.
• Monitor all processes on the server and wait for them to terminate.
• When all connections hit zero, stop the service you want to upgrade.
• Perform the service update
• Testing
• Monitor logs and possible alarms
• Be ready to rollback if necessary
• Send some low traffic and try to test service with internal users
• When everything is OK, tell the load balancers to send more traffic
• Wait, monitor everything, test, be sure
• Revert changes on the load balancers so that the specific server can take equal traffic/connection as the others.

This procedure is well established in such environments, and gives us the benefit of working with the whole team in working hours without the need of scheduling a maintenance window in the middle of the night, when low customer traffic is reaching us. During the day, if something is not going as planned, we can also reach other departments and work with them, figuring out what is happening.

Configuration Management

We are using ansible as the main configuration management tool. Every file, playbook, role, task of ansible is under a version control system, so that we can review changes before applying them to production. Viewing diffs from a modern web tool can be a lifesaver in these days.

Virtualization

We also use docker images or virtual images as development machines, so that we can perform any new configuration, update/upgrade on those machines and test it there.

Ansible Inventory

To perform service updates with ansible on servers, we are using the ansible inventory to host some metadata (aka variables) for every machine in a serverfarm. Let me give you an example:

[serverfarm001]
server01 version=1.2.3
server02 version=1.2.3
server03 version=1.2.3
server04 version=1.2.4

And performing the update action via ansible limits

eg.

~> ansible-playbook serverfarm001.yml -t update -C -D -l server04

Rollback

When something is not going as planned, we revert the changes on ansible (version control) and re-push the previous changes on a system. Remember the system is not getting any traffic from the front-end routers.

The Update

I was ready to do the update. Nagios was opened, logs were tailed -f

and then:

~> ansible-playbook serverfarm001.yml -t update

The Mistake

I run the ansible-playbook without limiting the server I wanted to run the update !!!

So all new changes passed through all servers, at once!

On top of that, new configuration broke running software with previous version. When the restart notify of service occurred every server simple stopped!!!

Funny thing, the updated machine server04 worked perfectly, but no traffic was reaching through the load balancers to this server.

Activate Rollback

It was time to run the rollback procedure.

Reverting changes from version control is easy. Took me like a moment or something.
Running again:

~> ansible-playbook serverfarm001.yml

and …

Waiting for Nagios

In 2,5 minutes I had fixed the error and I was waiting for nagios to be green again.

Then … Nothing! Red alerts everywhere!

Oh-Shit Moment

It was time for me to inform everyone what I have done.
Explaining to my colleagues and manager the mistake and trying to figuring out what went wrong with the rollback procedure.

Collaboration

On this crucial moment everything else worked like clockwise.

My colleagues took every action to:

• informing helpdesk
• looking for errors
• tailing logs
• monitor graphs
• viewing nagios
• talking to other people
• do the leg-work in general

and leaving me in piece with calm to figure out what went wrong.

I felt so proud to be part of the team at that specific moment.

If any of you reading this article: Truly thank all guys and gals .

Work-Around

I bypass ansible and copied the correct configuration to all servers via ssh.
My colleagues were telling me the good news and I was going through one by one of ~xx servers.
In 20minutes everything was back in normal.
And finally nagios was green again.

Blameless Post-Mortem

It was time for post-mortem and of course drafting the company’s incident report.

We already knew what happened and how, but nevertheless we need to write everything down and try to keep a good timeline of all steps.
This is not only for reporting but also for us. We need to figure out what happened exactly, do we need more monitoring tools?
Can we place any failsafes in our procedures? Also why the rollback procedure didnt work.

Fixing Rollback

I am writing this paragraph first, but to be honest with you, it took me some time getting to the bottom of this!

Rollback procedure actually is working as planned. I did a mistake with the version control system.

What we have done is to wrap ansible under another script so that we can select the version control revision number at runtime.
This is actually pretty neat, cause it gives us the ability to run ansible with previous versions of our configuration, without reverting in master branch.

The ansible wrapper asks for revision and by default we run it with [tip].

So the correct way to do rollbacks is:

eg.

~> ansible-playbook serverfarm001.yml -rev 238

At the time of problem, I didnt do that. I thought it was better to revert all changes and re-run ansible.
But ansible was running into default mode with tip revision !!

Although I manage pretty well on panic mode, that day my brain was frozen!

Re-Design Ansible

I wrap my head around and tried to find a better solution on performing service updates. I needed to change something that can run without the need of limit in ansible.

The answer has obvious in less than five minutes later:

files/serverfarm001/1.2.3
files/serverfarm001/1.2.4

I need to keep a separated configuration folder and run my ansible playbooks with variable instead of absolute paths.

eg.

- copy: src=files/serverfarm001/{{version}} dest=/etc/service/configuration

That will suffice next time (and actually did!). When the service upgrade is finished, We can simple remove the previous configuration folder without changing anything else in ansible.

Ansible Groups

Another (more simplistic) approach is to create a new group in ansible inventory.
Like you do with your staging Vs production environment.

eg.

[serverfarm001]
server01 version=1.2.3
server02 version=1.2.3
server03 version=1.2.3

[serverfarm001_new]
server04 version=1.2.4

and create a new yml file

---
- hosts: serverfarm001_new

run the ansible-playbook against the new serverfarm001_new group .

Validation

A lot of services nowadays have syntax check commands for their configuration.

You can use this validation process in ansible!

here is an example from ansible docs:

# Update sshd configuration safely, avoid locking yourself out
- template:
    src: etc/ssh/sshd_config.j2
    dest: /etc/ssh/sshd_config
    owner: root
    group: root
    mode: '0600'
    validate: /usr/sbin/sshd -t -f %s
    backup: yes

or you can use registers like this:

  - name: Check named
    shell: /usr/sbin/named-checkconf -t /var/named/chroot
    register: named_checkconf
    changed_when: "named_checkconf.rc == 0"
    notify: anycast rndc reconfig

Conclusion

Everyone makes mistakes. I know, I have some oh-shit moments in my career for sure. Try to learn from these failures and educate others. Keep notes and write everything down in a wiki or in whatever documentation tool you are using internally. Always keep your calm. Do not hide any errors from your team or your manager. Be the first person that informs everyone. If the working environment doesnt make you feel safe, making mistakes, perhaps you should think changing scenery. You will make a mistake, failures will occur. It is a well known fact and you have to be ready when the time is up. Do a blameless post-mortem. The only way a team can be better is via responsibility, not blame. You need to perform disaster-recovery scenarios from time to time and test your backup. And always -ALWAYS- use a proper configuration management tool for all changes on your infrastructure.

post scriptum

After writing this draft, I had a talk with some friends regarding the cloud industry and how this experience can be applied into such environment. The quick answer is you SHOULD NOT.

Working with cloud, means you are mostly using virtualization. Docker images or even Virtual Machines should be ephemeral. When it’s time to perform upgrades (system patching or software upgrades) you should be creating new virtual machines that will replace the old ones. There is no need to do it in any other way. You can rolling replacing the virtual machines (or docker images) without the need of stopping the service in a machine, do the upgrade, testing, put it back. Those ephemeral machines should not have any data or logs in the first place. Cloud means that you can (auto) scale as needed it without thinking where the data are.

thanks for reading.

CAA

Reading RFC 6844 you will find the definition of “DNS Certification Authority Authorization (CAA) Resource Record”.

You can read everything here: RFC 6844

So, what is CAA anyhow?

Certificate Authority

In a nutshell you are declaring which your Certificate Authority is for your domain.

It’s another way to verify that the certificate your site is announcing is in fact signed by the issuer that the certificate is showing.

So let’s see what my certificate is showing:

DNS

Now, let’s find out what my DNS is telling us:

# dig caa balaskas.gr 

;; ANSWER SECTION:
balaskas.gr.        5938    IN  CAA 1 issue "letsencrypt.org"

Testing

You can also use the Qualys ssl server test:

https://www.ssllabs.com/ssltest/

Postfix

smtp Vs smtpd

• postfix/smtp
  • The SMTP daemon is for sending emails to the Internet (outgoing mail server).
• postfix/smtpd
  • The SMTP daemon is for receiving emails from the Internet (incoming mail server).

TLS

Encryption on mail transport is what we call: opportunistic. If both parties (sender’s outgoing mail server & recipient’s incoming mail server) agree to exchange encryption keys, then a secure connection may be used. Otherwise a plain connection will be established. Plain as in non-encrypted aka cleartext over the wire.

SMTP - Outgoing Traffic

In the begging there where only three options in postfix:

• none
• may
• encrypt

The default option on a Centos 6x is none:

# postconf -d | grep smtp_tls_security_level
smtp_tls_security_level =

Nowadays, postfix supports more options, like:

• dane
• verify
• secure

Here is the basic setup, to enable TLS on your outgoing mail server:

smtp_tls_security_level = may
smtp_tls_loglevel = 1

From postfix v2.6 and later, can you disable weak encryption by selecting the cipher suite and protocols you prefer to use:

smtp_tls_ciphers = export
smtp_tls_protocols = !SSLv2, !SSLv3

You can also define where the file that holds all the root certificates on your linux server is, and thus to verify the certificate that provides an incoming mail server:

smtp_tls_CAfile = /etc/pki/tls/certs/ca-bundle.crt

I dont recommend to go higher with your setup, cause (unfortunately) not everyone is using TLS on their incoming mail server!

SMTPD - Incoming Traffic

To enable TLS in your incoming mail server, you need to provide some encryption keys aka certificates!

I use letsencrypt on my server and the below notes are based on that.

Let’s Encrypt

A quick explanation on what exists on your letsencrypt folder:

# ls -1 /etc/letsencrypt/live/example.com/

privkey.pem    ===>  You Private Key
cert.pem       ===>  Your Certificate
chain.pem      ===>  Your Intermediate
fullchain.pem  ===>  Your Certificate with Your Intermediate 

Postfix

Below you can find the most basic configuration setup you need for your incoming mail server.

smtpd_tls_ask_ccert = yes
smtpd_tls_security_level = may
smtpd_tls_loglevel = 1

Your mail server is asking for a certificate so that a trusted TLS connection can be established between outgoing and incoming mail server.
The servers must exchange certificates and of course, verify them!

Now, it’s time to present your own domain certificate to the world. Offering only your public certificate cert.pem isnt enough. You have to offer both your certificate and the intermediate’s certificate, so that the sender’s mail server can verify you, by checking the digital signatures on those certificates.

smtpd_tls_cert_file = /etc/letsencrypt/live/example.com/fullchain.pem
smtpd_tls_key_file = /etc/letsencrypt/live/example.com/privkey.pem

smtpd_tls_CAfile = /etc/pki/tls/certs/ca-bundle.crt
smtpd_tls_CApath = /etc/pki/tls/certs

CAfile & CApath helps postfix to verify the sender’s certificate by looking on your linux distribution file, that holds all the root certificates.

And you can also disable weak ciphers and protocols:

smtpd_tls_ciphers = high
smtpd_tls_exclude_ciphers = aNULL, MD5, EXPORT
smtpd_tls_protocols = !SSLv2, !SSLv3

Logs

Here is an example from gmail:

SMTPD - Incoming Mail from Gmail

You can see that there is a trusted TLS connection established From google:

Jun  4 11:52:07 kvm postfix/smtpd[14150]:
        connect from mail-oi0-x236.google.com[2607:f8b0:4003:c06::236]
Jun  4 11:52:08 kvm postfix/smtpd[14150]:
        Trusted TLS connection established from mail-oi0-x236.google.com[2607:f8b0:4003:c06::236]:
        TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)
Jun  4 11:52:09 kvm postfix/smtpd[14150]:
        4516420F32: client=mail-oi0-x236.google.com[2607:f8b0:4003:c06::236]
Jun  4 11:52:10 kvm postfix/smtpd[14150]:
        disconnect from mail-oi0-x236.google.com[2607:f8b0:4003:c06::236]

SMTP - Outgoing Mail from Gmail

And this is the response To gmail :

Jun  4 12:01:32 kvm postfix/smtpd[14808]:
        initializing the server-side TLS engine
Jun  4 12:01:32 kvm postfix/smtpd[14808]:
        connect from example.com[2a00:1838:20:1::XXXX:XXXX]
Jun  4 12:01:33 kvm postfix/smtpd[14808]:
        setting up TLS connection from example.com[2a00:1838:20:1::XXXX:XXXX]
Jun  4 12:01:33 kvm postfix/smtpd[14808]:
        example.com[2a00:1838:20:1::XXXX:XXXX]: TLS cipher list "aNULL:-aNULL:ALL:!EXPORT:!LOW:!MEDIUM:+RC4:@STRENGTH:!aNULL:!MD5:!EXPORT:!aNULL"
Jun  4 12:01:33 kvm postfix/smtpd[14808]:
        Anonymous TLS connection established from example.com[2a00:1838:20:1::XXXX:XXXX]:
        TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)
Jun  4 12:01:35 kvm postfix/smtpd[14808]:
        disconnect from example.com[2a00:1838:20:1::XXXX:XXXX]

As you can see -In both cases (sending/receiving)- the mail servers have established a trusted secure TLSv1.2 connection.
The preferred cipher (in both scenarios) is : ECDHE-RSA-AES128-GCM-SHA256

IPv6

Tell postfix to prefer ipv6 Vs ipv4 and use TLS if two mail servers support it !

#IPv6
smtp_address_preference = ipv6

What is the time?

Time offset is the amount of time that is off (or drift) from a specific value. In Linux systems, date is been calculating from the beginning of time. That is 00:00:00 1 January 1970 or as it called Unix Time and systems define date (time) as the number of seconds that have elapsed from 01.01.1970.

It is so important that even a few seconds off can cause tremendous disaster in data centers and applications.

Network Time

To avoid problems with time, systems must and should synchronize their time over the Internet every now and then. This is being done by asking a central NTP server via Network Time Protocol. The most common scenario for infrastructures is to have one or two NTP servers and then all the systems inside this infrastructure can synchronize their time from those machines.

Nagios - NRPE

In my case, I have a centralized NTP Daemon that runs on the Nagios Linux machine. That gives me the opportunity to check the EPOCH time of any system in my infrastructure against the time that the Nagios Server has.

Nagios Check

This is the script I am using:

# ebal, Thu, 11 May 2017 12:08:50 +0000

# EPOCH
TIME=$1
WARN=5
CRIT=10

# seconds
OFFSET=$( echo $(( $(date -d 'now ' +%s) - ${TIME} )) | sed -e 's#-##g' )

if [ "${OFFSET}" -lt "${WARN}" ]; then
        echo "OK"
        exit 0
elif [ "${OFFSET}" -ge "${CRIT}" ]; then
        echo "CRITICAL- ${OFFSET}"
        exit 2
elif [ "${OFFSET}" -lt "${CRIT}" ]; then
        echo "WARNING- ${OFFSET}"
        exit 1
else
        echo "UNKNOWN- ${OFFSET}"
        exit 3
fi

In a nutshell the script gets as the first argument an epoch time and calculate the diff between it’s own epoch time and that.

Example

./check_time_offset $(date -d 'now + 1 min' +%s)

The output is this:

CRITICAL- 60

Nrpe Configuration

This is the configuration for nrpe to run the check_time_offset

# tail -1 /etc/nrpe.d/time_offset.cfg

command[check_time_offset]=/usr/lib64/nagios/plugins/check_time_offset $ARG1$

Nagios Configuration

and this is my nagios configuration setup to use a remote nrpe :

define service{
        use                             service-critical
        hostgroup_name                  lnxserver01
        service_description             time_offset
        check_command                   check_nrpe!check_time_offset!$TIMET$
        }

Take a minute to observer a little better the nrpe command.

check_nrpe!check_time_offset!$TIMET$

TIMET

I was having problems passing the nagios epoch time as an argument on the definition of the above service.

Testing the nrpe command as below, I was getting the results I was looking for:

./check_nrpe -H lnxserver01 -c check_time_offset -a $(date -d 'now + 6 sec' +%s)

But is there a way to pass as a nagios argument the output of a command ?

• No

A dear colleague of mine mentioned nagios macros:

Standard Macros in Nagios

$TIMET$     Current time stamp in time_t format (seconds since the UNIX epoch)

Perfect !!!

The problem

The last couple weeks, a backup server I am managing is failing to make backups!

The backup procedure (a script via cron daemon) is to rsync data from a primary server to it’s /backup directory. I was getting cron errors via email, informing me that the previous rsync script hasnt already finished when the new one was starting (by checking a lock file). This was strange as the time duration is 12hours. 12 hours werent enough to perform a ~200M data transfer over a 100Mb/s network port. That was really strange.

This is the second time in less than a year that this server is making problems. A couple months ago I had to remove a faulty disk from the software raid setup and check the system again. My notes on the matter, can be found here:

https://balaskas.gr/blog/2016/10/17/linux-raid-mdadm-md0/

Identify the problem

So let us start to identify the problem. A slow rsync can mean a lot of things, especially over ssh. Replacing network cables, viewing dmesg messages, rebooting servers or even changing the filesystem werent changing any things for the better. Time to move on the disks.

Manage and Monitor software RAID devices

On this server, I use raid5 with four hard disks:

# mdadm --verbose --detail /dev/md0

/dev/md0:
        Version : 1.2
  Creation Time : Wed Feb 26 21:00:17 2014
     Raid Level : raid5
     Array Size : 2929893888 (2794.16 GiB 3000.21 GB)
  Used Dev Size : 976631296 (931.39 GiB 1000.07 GB)
   Raid Devices : 4
  Total Devices : 4
    Persistence : Superblock is persistent

    Update Time : Sun May  7 11:00:32 2017
          State : clean
 Active Devices : 4
Working Devices : 4
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 512K

           Name : ServerTwo:0  (local to host ServerTwo)
           UUID : ef5da4df:3e53572e:c3fe1191:925b24cf
         Events : 10496

    Number   Major   Minor   RaidDevice State
       4       8       16        0      active sync   /dev/sdb
       1       8       32        1      active sync   /dev/sdc
       6       8       48        2      active sync   /dev/sdd
       5       8        0        3      active sync   /dev/sda

View hardware parameters of hard disk drive

aka test the hard disks:

# hdparm -Tt /dev/sda

/dev/sda:
 Timing cached reads:   2490 MB in  2.00 seconds = 1245.06 MB/sec
 Timing buffered disk reads: 580 MB in  3.01 seconds = 192.93 MB/sec

# hdparm -Tt /dev/sdb

/dev/sdb:
 Timing cached reads:   2520 MB in  2.00 seconds = 1259.76 MB/sec
 Timing buffered disk reads: 610 MB in  3.00 seconds = 203.07 MB/sec

# hdparm -Tt /dev/sdc

/dev/sdc:
 Timing cached reads:   2512 MB in  2.00 seconds = 1255.43 MB/sec
 Timing buffered disk reads: 570 MB in  3.01 seconds = 189.60 MB/sec

# hdparm -Tt /dev/sdd

/dev/sdd:
 Timing cached reads:     2 MB in  7.19 seconds = 285.00 kB/sec
 Timing buffered disk reads:   2 MB in  5.73 seconds = 357.18 kB/sec

Root Cause

Seems that one of the disks (/dev/sdd) in raid5 setup, is not performing as well as the others. The same hard disk had a problem a few months ago.

What I did the previous time, was to remove the disk, reformatting it in Low Level Format and add it again in the same setup. The system rebuild the raid5 and after 24hours everything was performing fine.

However the same hard disk seems that still has some issues . Now it is time for me to remove it and find a replacement disk.

Remove Faulty disk

I need to manually fail and then remove the faulty disk from the raid setup.

Failing the disk

Failing the disk manually, means that mdadm is not recognizing the disk as failed (as it did previously). I need to tell mdadm that this specific disk is a faulty one:

# mdadm --manage /dev/md0 --fail /dev/sdd
mdadm: set /dev/sdd faulty in /dev/md0

Removing the disk

now it is time to remove the faulty disk from our raid setup:

# mdadm --manage /dev/md0 --remove  /dev/sdd
mdadm: hot removed /dev/sdd from /dev/md0

Show details

# mdadm --verbose --detail /dev/md0

/dev/md0:
        Version : 1.2
  Creation Time : Wed Feb 26 21:00:17 2014
     Raid Level : raid5
     Array Size : 2929893888 (2794.16 GiB 3000.21 GB)
  Used Dev Size : 976631296 (931.39 GiB 1000.07 GB)
   Raid Devices : 4
  Total Devices : 3
    Persistence : Superblock is persistent

    Update Time : Sun May  7 11:08:44 2017
          State : clean, degraded
 Active Devices : 3
Working Devices : 3
 Failed Devices : 0
  Spare Devices : 0

         Layout : left-symmetric
     Chunk Size : 512K

           Name : ServerTwo:0  (local to host ServerTwo)
           UUID : ef5da4df:3e53572e:c3fe1191:925b24cf
         Events : 10499

    Number   Major   Minor   RaidDevice State
       4       8       16        0      active sync   /dev/sdb
       1       8       32        1      active sync   /dev/sdc
       4       0        0        4      removed
       5       8        0        3      active sync   /dev/sda

Mounting the Backup

Now it’s time to re-mount the backup directory and re-run the rsync script

mount /backup/

and run the rsync with verbose and progress parameters to review the status of syncing

/usr/bin/rsync -zravxP --safe-links --delete-before --partial --protect-args -e ssh 192.168.2.1:/backup/ /backup/

Everything seems ok.

A replacement order has already been placed.

Rsync times manage to hit ~ 10.27MB/s again!

rsync time for a daily (12h) diff is now again in normal rates:

real    15m18.112s
user    0m34.414s
sys     0m36.850s

PowerDNS

My Authoritative PowerDNS configuration, is relatively simple:

Configuration

Here is my configuration:

# egrep -v '^($|#)' pdns.conf

guardian=yes
launch=bind
bind-config=/etc/pdns/named.conf
local-address=MY_IPv4_ADDRESS
local-ipv6=MY_IPv6_ADDRESS
setgid=pdns
setuid=pdns

Bind Backend

I am using a bind backend because I used to run a bind dns server and I am too lazy to change it.

the named.conf doesnt have much:

zone "balaskas.gr" IN {
    type master;
    file "/etc/pdns/var/balaskas.gr";
};

Logs

Today, I’ve noticed some unusual traffic to my server, so I’ve enabled the logging features:

log-dns-details=yes
log-dns-queries=yes
query-logging=yes

DDoS

The horror !!!

In less than 10minutes or so, almost 2500 “unique” IPs were “attacking” my auth-dns with random queries.

Let me give you an example:

utmzcnqjytkpmnop.madingyule.net
gdqlozsdqngdidkb.madingyule.net
wrojktwlwhevwtup.madingyule.net
enozexazqxoj.madingyule.net
izahejotetwlkhql.madingyule.net

IPtables

iptables to the rescue:

iptables -I INPUT -m string --algo bm --string "madingyule" -j DROP

Any dns query with the string madingyule will be blocked in INPUT chain with Boyer–Moore string search algorithm.

dnsdist

I need a more permanent solution than reading logs and block attacks with iptables, so I’ve asked the IRC about it. They pointed me to dnsdist.

I’ve already knew about dnsdist but I always thought it was a solution for recursors and not for auth-ns.

I was wrong! dnsdist is a highly DNS-, DoS- and abuse-aware loadbalancer and works fine for auth-ns setup too.

pdns configuration

My auth-ns configuration had to change to something like this:

any-to-tcp=no
disable-tcp=yes
dname-processing=yes
guardian=yes
launch = bind
bind-config = /etc/pdns/named.conf
local-address=127.0.0.1
local-port=5353

Disabling any global listener and tcp.

dnsdist configuration

here is my dnsdist configuration:

/etc/dnsdist/dnsdist.conf

-- accept DNS queries on UDP and TCP
addLocal("MY_IPv4_IP:53")
addLocal("[MY_IPv6_IP]:53")

-- fwd queries to localhost
newServer({address="127.0.0.1:5353"})

-- resets the list to this array
setACL("::/0")
addACL("0.0.0.0/0")

I am not 100% sure about the ACL but everything seems ok.

Thats it !!!! - Finished

dnsdist - client

To connect to the dnsdist daemon, you need to add the below configuration:

controlSocket("127.0.0.1")

That means, after reloading the daemon, you can connect on it with:

# dnsdist -c

Extra

Logs

 -- log everything
 addAction(AllRule(), LogAction("/var/log/dnsdist.log", false, true, false))

Domain Blocking

Let’s start with the above iptables example:

addDomainBlock("wanbo88.net.")

addDomainBlock("madingyule.net.")

You can connect to dnsdist client (see above) and and any domain you wan to block without restarting your dnsdist service.

Allow Action

Another trick you can do, is to create some custom rules by allowing any DNS queries for your domains and drop any other dns query. You can do this with something like that:

addAction(makeRule("balaskas.gr.")   , AllowAction())
addAction(makeRule("ebalaskas.gr.")  , AllowAction())

addAction(AllRule()                  , DropAction())

Rule Order

Just remember, that the rules will be processed in line order of the file.

Block ANY

You can drop all ANY queries with:

addAction(QTypeRule(dnsdist.ANY), DropAction())

although I dont recommend it.

Rate-Limiting - QPS (Queries Per Second)

Now to the good stuff: rate limiting

A simple rule is something like the below:

-- drop queries exceeding 5 qps, grouped by /24 for IPv4 and /64 for IPv6
addAction(MaxQPSIPRule(5, 24, 64), DropAction())

If you want to drop everything when they pass the 5qps:

addAction(MaxQPSIPRule(5), DropAction())

Delay

An alternative approach is to delay everything for more than 5qps (rate limiting), this may make the bot (ddos) to overlook you.

-- Delay for 1000ms aka 1s for 5qps
addDelay(MaxQPSIPRule(5), 1000)

File Descriptors

Working on a VPS (virtual private server), I’ve troubled with file descriptors.
Message in logs from dnsdist is:

Warning, this configuration can use more than 1057 file descriptors, web server and console connections not included, and the current limit is 1024

From the command line you can tweak it to 2048 like this:

# ulimit -n 2048

If you need to make it permanent:

vim /etc/security/limits.conf

*        -        nofile        2048

Traffic

okei, it’s time to see what’s the traffic:

topQueries(20,2)

will report the domains that are reaching to our dnsdsist.

topQueries() will report everything

topQueries(20,1)

will report TLD (Top Level Domains)

Identify your traffic:

grepq("balaskas.gr")

Monit

So dnsdist is now in front of my powerdns auth-ns setup and handles everything, blocking what is necessary.

To be sure that the daemon is up and running:

/etc/monit.d/dnsdist.monit

check process dnsdist with pidfile /var/run/dnsdist.pid
    alert evaggelos_AT_balaskas_DOT_gr only on { timeout, nonexist }
    start program = "/etc/init.d/dnsdist start"
    stop program  = "/etc/init.d/dnsdist stop"

dnsdist - basics

Some basic commands about dnsdist (when connecting to the client):

Commands:

addAction(                         addAnyTCRule()                     addDelay(
addDisableValidationRule(          addDNSCryptBind(                   addDomainBlock(
addDomainSpoof(                    addDynBlocks(                      addLocal(
addLuaAction(                      addNoRecurseRule(                  addPoolRule(
addQPSLimit(                       addQPSPoolRule(                    addResponseAction(
AllowAction()                      AllowResponseAction()              AllRule()
AndRule(                           benchRule(                         carbonServer(
clearDynBlocks()                   clearQueryCounters()               clearRules()
controlSocket(                     DelayAction(                       DelayResponseAction(
delta()                            DisableValidationAction()          DropAction()
DropResponseAction()               dumpStats()                        exceedNXDOMAINs(
exceedQRate(                       exceedQTypeRate(                   exceedRespByterate(
exceedServFails(                   firstAvailable                     fixupCase(
generateDNSCryptCertificate(       generateDNSCryptProviderKeys(      getPoolServers(
getQueryCounters(                  getResponseRing()                  getServer(
getServers()                       grepq(                             leastOutstanding
LogAction(                         makeKey()                          MaxQPSIPRule(
MaxQPSRule(                        mvResponseRule(                    mvRule(
newDNSName(                        newQPSLimiter(                     newRemoteLogger(
newRuleAction(                     newServer(                         newServerPolicy(
newSuffixMatchNode()               NoRecurseAction()                  PoolAction(
printDNSCryptProviderFingerprint(  QNameLabelsCountRule(              QNameWireLengthRule(
QTypeRule(                         RCodeRule(                         RegexRule(
registerDynBPFFilter(              RemoteLogAction(                   RemoteLogResponseAction(
rmResponseRule(                    rmRule(                            rmServer(
roundrobin                         setACL(                            setAPIWritable(
setDNSSECPool(                     setECSOverride(                    setECSSourcePrefixV4(
setECSSourcePrefixV6(              setKey(                            setLocal(
setMaxTCPClientThreads(            setMaxTCPQueuedConnections(        setMaxUDPOutstanding(
setQueryCount(                     setQueryCountFilter(               setRules(
setServerPolicy(                   setServerPolicyLua(                setServFailWhenNoServer(
setTCPRecvTimeout(                 setTCPSendTimeout(                 setUDPTimeout(
setVerboseHealthChecks(            show(                              showACL()
showDNSCryptBinds()                showDynBlocks()                    showResponseLatency()
showResponseRules()                showRules()                        showServerPolicy()
showServers()                      showTCPStats()                     showVersion()
shutdown()                         SpoofAction(                       TCAction()
testCrypto()                       topBandwidth(                      topClients(
topQueries(                        topResponseRule()                  topResponses(
topRule()                          topSlow(                           truncateTC(
unregisterDynBPFFilter(            webserver(                         whashed
wrandom                            addACL(                            

dnsdist - ACL

Keep in mind that the default ACL is:

> showACL()
127.0.0.0/8
10.0.0.0/8
100.64.0.0/10
169.254.0.0/16
192.168.0.0/16
172.16.0.0/12
::1/128
fc00::/7
fe80::/10

Log Rotate

/etc/logrotate.d/dnsdist

/var/log/dnsdist.log {
    rotate 7
    daily
    dateext
    delaycompress
    compress
    postrotate
        [ ! -f /var/run/dnsdist.pid ] || kill -USR1 `cat /var/run/dnsdist.pid`
    endscript
}

I’ve just finished listening the audio book version of Cyberspies: The Secret History of Surveillance, Hacking, and Digital Espionage by Gordon Corera and liked it.

As the name suggests, It is about the History of surveillance mostly in UK & US.

After upgrading one of my linux boxes from CentOS 6.8 to 6.9, I wanted to find out the files that I had to review. From experience I already knew what file names I should check: .rpmsave & .rpmnew

The command I usually type is: find

# find /etc/|egrep ".*rpm(save|new)$"

/etc/rc.d/init.d/postgrey.rpmsave
/etc/php.ini.rpmnew
/etc/sudoers.rpmnew
/etc/postfix/postgrey_whitelist_clients.local.rpmsave
/etc/sysctl.conf.rpmnew

a more nice way is to tell find to search for files with type: file to exclude any binary searches:

# find /etc/ -type f |egrep ".*rpm(save|new)$"

/etc/rc.d/init.d/postgrey.rpmsave
/etc/php.ini.rpmnew
/etc/sudoers.rpmnew
/etc/postfix/postgrey_whitelist_clients.local.rpmsave
/etc/sysctl.conf.rpmnew

but find is a very powerful command, and reading through the manual page:

-regex pattern

File name matches regular expression pattern. This is a match on the whole path, not a
search. For example, to match a file named ‘./fubar3’, you can use the regular expression
‘.bar.’ or ‘.b.3’, but not ‘f.r3’. The regular expressions understood by find are by
default Emacs Regular Expressions, but this can be changed with the -regextype option.

ok, we are getting somewhere. I can use -regex with an emacs regular expression pattern to search.

# find /etc/ -type f -regex ".*rpm(save|new)$"

Nothing in output !!! aka this is a “WAT ?????” moment.

Perhaps I am not typing an emacs regex.
Let’s try to use an alternative:

# find /etc/ -type f -regextype -name "*rpmsave$"

valid types are findutils-default',awk’, egrep',ed’, emacs',gnu-awk’, grep',posix-awk’, posix-basic',posix-egrep’, posix-extended',posix-minimal-basic’, `sed’.

With this typo, I can find out what the alternatives

ok, let’s try egrep or anything else:

# find /etc/ -type f -regex ".*rpm(save|new)$" -regextype sed

# find /etc/ -type f -regex ".*rpm(save|new)$" -regextype posix-egrep
# find /etc/ -type f -name ".*rpm(save|new)$" -regextype posix-egrep

# find /etc/ -type f -name ".*rpm(save|new)$" -regextype egrep
# find /etc/ -type f -name ".*rpm(save|new)$" -regextype sed
# find /etc/ -type f -name ".*rpmsave$" -regextype sed
# find /etc/ -type f -name ".*rpmsave$" -regextype posix-egrep
# find /etc/ -type f -name ".*rpmsave$" -regextype egrep

# find /etc/ -type f -regex ".*rpm(save)$" -regextype egrep
# find /etc/ -type f -regex ".*rpm(save|new)$" -regextype egrep

Nothing !!!

Am I typing this correctly ?

# find /etc/ -type f | egrep ".*rpm(save|new)$"

/etc/rc.d/init.d/postgrey.rpmsave
/etc/php.ini.rpmnew
/etc/sudoers.rpmnew
/etc/postfix/postgrey_whitelist_clients.local.rpmsave
/etc/sysctl.conf.rpmnew

then, what the h3ll?

Let’s read the manual page, once more:

The -daystart, -follow and -regextype options are different in this respect, and have an effect only on tests which appear later in the command line. Therefore, for clarity, it is best to place them at the beginning of the expression

Exhhmmmmm

I need to put -regextype before the regex.

# find /etc/ -type f -regextype egrep -regex ".*rpm(save|new)$"

/etc/rc.d/init.d/postgrey.rpmsave
/etc/php.ini.rpmnew
/etc/sudoers.rpmnew
/etc/postfix/postgrey_whitelist_clients.local.rpmsave
/etc/sysctl.conf.rpmnew

Yeah !

I’ve just finished listening the audiobook version of Ghost in the Wires: My Adventures as the World's Most Wanted Hacker and really liked it a lot.

Everything you need to know about social engineering on a previous era of technology.

Totally recommended on understanding the value of ethical hacking

Working with VPS (Virtual Private Server), sometimes means that you dont have a lot of memory.

That’s why, we use the swap partition, a system partition that our linux kernel use as extended memory. It’s slow but necessary when your system needs more memory. Even if you dont have any free partition disk, you can use a swap file to add to your linux system.

Create the Swap File

[root@centos7] # dd if=/dev/zero of=/swapfile count=1000 bs=1MiB
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 3.62295 s, 289 MB/s

[root@centos7] # du -sh /swapfile
1.0G    /swapfile

That is 1G file

Make Swap

[root@centos7] # mkswap -L swapfs /swapfile
Setting up swapspace version 1, size = 1048572 KiB
LABEL=swapfs, UUID=d8af8f19-5578-4c8e-b2b1-3ff57edb71f9

Permissions

[root@centos7] # chmod 0600 /swapfile

Activate

[root@centos7] # swapon /swapfile

Check

# free
              total        used        free      shared  buff/cache   available
Mem:        1883716     1613952       79172       54612      190592       64668
Swap:       1023996           0     1023996

fstab

Now for the final step, we need to edit /etc/fstab

/swapfile   swap    swap    defaults    0   0

The Phoenix Project: A Novel About IT, DevOps, and Helping Your Business Win (2013)

An amazing book about IT and devops philosophy, you have to read it.