Archive for the ‘CentOS’ Category

How to Copy Files with SCP between Linux Servers

Saturday, July 19, 2014 posted by Till

1.1 SCP Command Line-An Overview


The SCP command line is commonly used to copy files over SSH, and between popular Operating systems like Linux, Mac and Windows in a secure fashion. SCP is used to copy files to/from a remote server. It also allows you to copy files from one remote server to another remote server, without passing traffic through your PC.


1.2 Configuring the System of the Virtual Machine


At the outset, for sending files to the virtual machines, you would require a specific set of configuration, as explained below:

1. Open VirtualBox

2. Please select the virtual machine where your target system is running.

3. Open Settings > Network

4. Please select the correct Adapter tab (it will be the first one in case you have not made any changes so far)

5. You must select Bridged Adapterfrom the Attached to dropdown menu.

6. Now, you can run your virtual machine.


1.3 Initiating File Copy between Linux Servers Using SCP


Once begun, you must open a terminal and key in the following:

sudo apt-get install openssh-server

The ifconfig will throw up a few blocks, like the one titled eth0.

 ctest@ctest-System-Product-Name ~ $ ifconfig
eth0		Link encap:Ethernet  HWaddr f4:6d:04:94:8f:17
inet addr:  Bcast:  Mask:
          inet6 addr: fe80::f66d:4ff:fe94:8f17/64 Scope:Link
          RX packets:234392 errors:0 dropped:0 overruns:0 frame:0
          TX packets:128835 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:332109021 (332.1 MB)  TX bytes:11758082 (11.7 MB)
          Interrupt:43 Base address:0x6000

lo        Link encap:Local Loopback
          inet addr:  Mask:
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:39 errors:0 dropped:0 overruns:0 frame:0
          TX packets:39 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:2424 (2.4 KB)  TX bytes:2424 (2.4 KB)

ctest@ctest-System-Product-Name ~ $

The IP address exhibited on inet adress: is the one your machine would have in your internal network, and it will be the one you are going to access the machine under. Here, you must revisit the sender system now that you are aware of the IP of the receiver. If you possess the files to be sent, in addition to the directory for storing these on your virtual machine ready, you may simply go ahead and send the file by using the following command:

scp [path of file to send] root@[receiver's IP]:[target directory]

In the above command, you must replace the items in brackets [] with actual values.

For instance, if you wish to send a file titled MyVideo.mp4 housed in the /home/ctest/Videosdirectory to the /home/cooldude/Videos directory of the system that has an internal IP of, you must use the following command line:

scp /home/ctest/Videos/MyVideo.mp4 root@


1.4 Fixing Errors


Post entering the basic SCP command, you may encounter the following message:


ctest@ctest-System-Product-Name ~ $ scp /home/ctest/Videos/MyVideo.mp4 root@
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the ECDSA key sent by the remote host is
Please contact your system administrator.
Add correct host key in /home/ctest/.ssh/known_hosts to get rid of this message.
Offending ECDSA key in /home/ctest/.ssh/known_hosts:4
  remove with: ssh-keygen -f "/home/ctest/.ssh/known_hosts" -R
ECDSA host key for changed and you have requested strict checking.
Host key verification failed.
lost connection
ctest@ctest-System-Product-Name ~ $

More often than not, this is caused when the system with the given IP is no longer the same as it was when you last connected to the same IP. For instance, if you happened to host a new virtual machine that subsequently took the same IP as the old one.
To fix this one, you must follow the commands given in the message to remove the offending key (as shown below):

ssh-keygen -f "/home/ctest/.ssh/known_hosts" -R

You must ensure that you replace the path and the IP with the ones matching your specific inputs. You may also remove the key manually by opening the known_host file with the help of a texteditor, and removing the key (obviously as root).


1.5 Completing the Process


If, however, you do not come across any such issue, or you have managed to tackle the same, you would be asked if you really wish to proceed. You must key in yesand hit Enter to confirm the same.

Next, you’ll be asked for the root password of the receiver, which you must key in and before hitting Enter once again.

Now, the copied file must be accessible on the intended directory of the receiver, although you must not have any permissions to write/execute the same. If, however, you are seeking full permissions, please use the following command:

sudo chmod 777 /home/cooldude/Videos/MyVideo.mp4

Here, you must remember to change the path value to the one corresponding to your file, and you are good to go!

Solution for: system-config-firewall: command not found

Wednesday, February 5, 2014 posted by admin

When you get the error message "system-config-firewall: command not found" on your CentOS Server while trying to configure the firewall on the shell, then the text interface version of the firewall configuration utility is missing. Install it with this command:

yum install system-config-firewall-tui

Dovecot is watching the whole server filesystem for modifications and removed or added sub filesystems. If you get errors similar to this one on your server:

Aug 30 09:10:23 server1 dovecot: master: Warning: /var/www/clients/client1/web1/log is no longer mounted. If this is intentional, remove it with doveadm mount

 (the directory path may vary), then you can fix it by excluding the path from being watched by dovecot. In my case, dovecot shall not watch my website directories as they do not contain any mailboxes

Run the following command on the shell as root user:

doveadm mount add '/var/www/*' ignore

To exclude all files and folders in /var/www from deovecot monitoring.


If you get error messages from amavisd similar to the one posted below on a server which is virtualized with OpenVZ:

Mar  5 09:09:02 v100 amavis[17378]: (17378-14) (!!)TROUBLE in process_request: Error writing a SMTP response to the socket: Broken pipe at (eval 100) line 987, <GEN44> line 31.

then the issue can be caused by the NUMTCPSOCK value in the openvz limits. Even if the barrier of this limit was never met in /proc/user_beancounters, the above error occurs when more then 25% of all TCP sockets were used. The solution is to set the NUMTCPSOCK barrier and limit to a high value in the openvz container configuration file. Here a value that worked for me on a moderately used mailserver:


Finally restart the OpenVZ VM to apply the new limit value.


Apache mod_security settings for WordPress and ModX

Monday, January 7, 2013 posted by Till

If you use the apache mod_security module on your apache server, you might encounter wrong 403 errors for several URL's of the cms systems. Here are some exception rules to avoid that:

For WordPress Blogs

<locationmatch "/wp-admin/admin-ajax.php">
SecRuleRemoveById 300013
SecRuleRemoveById 300015
SecRuleRemoveById 300016
SecRuleRemoveById 300017

<locationmatch "/wp-admin/page.php">
SecRuleRemoveById 300013
SecRuleRemoveById 300015
SecRuleRemoveById 300016
SecRuleRemoveById 300017

<locationmatch "/wp-admin/post.php">
SecRuleRemoveById 300013
SecRuleRemoveById 300015
SecRuleRemoveById 300016
SecRuleRemoveById 300017

For the ModX CMS

<LocationMatch "/manager/index.php">
SecRuleRemoveById 300016

<LocationMatch "/connectors/resource/index.php">
SecRuleRemoveById 300013 300014 300015 300016

<LocationMatch "/connectors/element/tv.php">
SecRuleRemoveById 300013 300016

Add these rules inside the vhost file of the website. If you use ISPConfig to manage the server, then add the rules in the apache directives field of the website settings in ispconfig.

Many thanks to PlanetFox for providing the rules.

The following guide shows how to disable and remove mysql replication from two or more mysql servers. These steps can be used for master/slave and master/master mysql setups. The following SQL commands have to be be executed in phpmyadmin or with the mysql commandline program. It is just important that you are logged in as mysql root user. Below I will use the mysql commandline client.

Login into mysql as root user from commandline:

mysql -u root -p

the mysql command will ask for the mysql root password.

Then execute these commands if the installed mysql version is < 5.5.16:


use the commands below instead if the mysql version is > 5.5.16


Now edit the my.cnf file (/etc/mysql/my.cnf) and add a # in front of all lines that start with "replicate-" or "master-". Example:

# replicate-same-server-id = 0
# master-host =
# master-user = slaveuser
# master-password = akst6Wqcz2B
# master-connect-retry = 60

Then restart mysql:

/etc/init.d/mysql restart


Setting up email routing to gmail / google apps via ISPConfig 3

Thursday, November 29, 2012 posted by Till

The following guide describes the steps to add DNS records that route emails from a domain managed in ISPConfig 3 to google apps / gmail. The guide assumes that you have already setup the dns zone for your domain in ispconfig.

Login to ISPConfig, click on the DNS module icon in the upper navigation bar, then open the settings of the DNS zone that you want to redirect to google and click on the "records" tab. You should see a record list similar to this:

Now Delete the existing MX record and the "mail" A-Record. Then add the following new records:

CNAME Record:

Hostname: mail


IMPORTANT: All full domain names like "" have to end with a dot, if the dot is missing, the name is treated as subdomain of the zone.

The resulting record list should look like this:

Sometimes you are forced to compile packages from source because they are not present in your current distribution's package format, which can be really annoying. While this is the safer option, there is also a quicker alternative, which is converting existing packages into the one you need with alien.

sudo apt-get install alien

Before you use it, make sure to have read the alien man page!

man alien

If you're on Ubuntu for example and need a package that is only available in the rpm format, power your terminal and convert the package (the following is available as deb, it's just an example):

sudo alien clementine-1.0.1-1.fc16.x86_64.rpm

The package will then be converted. There are a few points that you should be aware of though:

- Dependencies of converted packages will not be resolved. If you install it anyway, your update manager may notice the missing dependencies and install them however.
- It is not recommended to use alien for critical packages. The man page gives further info on that.

Using document templates in Linux

Tuesday, June 26, 2012 posted by CSch

The usual thing you find when you right-click your desktop to create a new document is the option to create an empty text document. This selection can be widened however by using the Templates folder in your home folder. Any document that is put in there will be selectable; this is also possible with pictures and other formats. Pinguy OS for example provides and excellent working system out of the box and comes with multiple file templates installed:

The string Untitled is put in front every newly created document from a template. To remove an item from the list, just remove it from your Templates folder. By making a document invisible in the Templates folder it is also removed from the list.

The majority of graphical environments let you choose to remember the passwords you enter somewhere to ease access to something but they usually don't tell you how to delete them again. Most Linux desktop distributions have a tool installed where all your saved passwords for network drives are stored in that is called Passwords and Keys.

You can find the saved passwords right on the first Passwords tab. Right-click the one you want to remove and select Delete. Confirm your choice by clicking Delete again on the window that pops up.