FAQforge provides answers for frequently asked questions for the Linux-, MAC and Windows operating systems.

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
ifconfig

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:192.168.0.11  Bcast:192.168.0.255  Mask:255.255.255.0
          inet6 addr: fe80::f66d:4ff:fe94:8f17/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          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:127.0.0.1  Mask:255.0.0.0
          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 191.167.1.61, you must use the following command line:

scp /home/ctest/Videos/MyVideo.mp4 root@191.167.1.61:/home/cooldude/Videos

 

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@191.167.1.61:/home/cooldude/Videos
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@  WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
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
4e:c0:50:9a:cf:b6:bc:45:ed:9b:54:97:d8:11:21:a8.
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 191.167.1.61
ECDSA host key for 191.167.1.61has 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 191.167.1.61

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

If your mail server stops working (neither incoming nor outgoing email works) and you find the following error message in the mail.log file:

fatal: open database /var/lib/postfix/smtpd_scache.db: File exists

then the smtpd_scache.db might got corrupted. Postfix will recreate this file, if it does not exist. So it can be removed to solve the issue:

/etc/init.d/postfix stop
rm -f /var/lib/postfix/smtpd_scache.db
/etc/init.d/postfix start

Thanks to Alexander Fox for sending me this FAQ.

Enable virtualization on Gigabyte Z77X-UDH3 motherboard BIOS

Monday, October 7, 2013 - posted by CSch

To enable virtualization on a machine with a Z77X-UDH3 motherboard run the BIOS by hitting Del while booting the computer.

Once inside click on the BIOS Features tab and look for the Intel Virtualization Technology entry. If it's set on Disabled, set it on Enabled. Afterwards save the changes made to your settings and quit the BIOS using the last tab from the main tab-line.

Virtualbox: VT-X is not available

Thursday, October 3, 2013 - posted by CSch

In some cases when you try to get a virtual machine running with Virtualbox or similar virtualization software you will get an error stating that 'VT-X is not available'. This relates to BIOS settings which, depending on your processor, determine whether your computer is able to virtualize stuff. These settings are not set automatically however, so it's worth a look into your BIOS whether you can actually change the setting and if your processor allows it.

The keyword to look for in the settings is 'Virtualization', it's probably placed in some advanced tab if there are some of those in your BIOS.

To see how it's done with a Z77X-UDH3 motherboard by Gigabyte see this post: Gigabyte Z77X-UDH3

While SkyDrive needed complex folder mapping to be accessed from your computer's file system in the past it is now possible to download a desktop app from the Microsoft website: http://windows.microsoft.com/en-us/skydrive/download

Scroll down and click the Download the desktop app button to start downlowding. Install it afterwards by double-clicking the executable:

skydrive1After the installation your SkyDrive folder will be placed in your User's folder by default:

skydrive2

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.

 

Disable Opera mouse gestures

Friday, August 23, 2013 - posted by CSch

The Opera browser uses mouse gestures that allow the user to navigate through tabs and tab histories with the help of mouse-clicks and -movements. This can be a hindrance however if you are used to control the browser with its own graphical interface and often just play around with your mouse out of boredom.

To disable these gestures you simply need to open an Opera window and go to Settings > Preferences > Advanced > Shortcuts and uncheck the Enable mouse gestures checkbox.

How to change Windows 7′s default fonts

Monday, August 19, 2013 - posted by CSch

Windows 7 has hidden away some features and options pretty neatly but nonetheless they still exist. Such as the option to change the system fonts. To get there try searching for Change window colors and metrics in the Start menu (metrics is also sufficient).

Hit enter if you have found it and you will be guided right to the fonts window where you can change the font and size of all the Windows fonts. And since we all love Comic Sans, why not use that on every option?

11

Create ‘Recently Added’ playlist in Windows Media Player

Friday, August 16, 2013 - posted by CSch

To create a playlist in WMP that only plays recently added is pretty simple if you know how. Open WMP to get started and in the same bar that you find the Search panel in click on Create Playlist > Create auto playlist. A window will open where you can enter the name of the auto-playlist as well as the conditions that must be given move music into the list:

12

Click on the topmost green plus-icon to add a condition and select Date Added - the player will automatically build it and set it to include everything that's been added to the media library in the last 30 days. You can edit that or leave it like this and by pressing okay create the playlist!