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Over 80% is running on some form of Linux – so does your Mac and you iPhone. Sometimes we have to get our hands dirty on the command line – it makes you feel like a proper hacker.

Here are some pointers I picked up on my journey.

  • Jay Versluis 11:01 am on August 14, 2015 Permalink | Reply
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    Categories: Linux ( 70 )

    How to disable the user list at login on CentOS 7 

    Screen Shot 2015-08-13 at 10.51.47

    By default, CentOS 7 will display a list of all users on the system. Click on it, type in the password, and you’re in. This works well when you have a handful of users on the system.

    However, on systems with a lot of users, not everyone can be displayed in that list – and scrolling up or down is impossible (and even if it was, it’s impractical at best). The solution is to replace that list with a box to type in a user, much like what would happen when you choose the “Not Listed” option.

    Here’s how to do it:

    From the command line, login as root and create a file called /etc/dconf/db/gdm.d/00-login-screen. By default it does not exist.

    vi /etc/dconf/db/gdm.d/00-login-screen

    Now add the following lines to it and save the file:

    [org/gnome/login-screen]
    # Do not show the user list
    disable-user-list=true
    

    This will tell GNOME not to display the list anymore, and instead bring up a text box as shown below. For the change to take effect, we need to update GNOME with the following command:

    dconf update

    And that’s it!

    Screen Shot 2015-08-13 at 10.54.55





     
  • Jay Versluis 10:48 am on August 13, 2015 Permalink | Reply
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    Categories: Linux ( 70 )

    How to enable automatic user logins in CentOS 7 and GNOME 

    CentOS-LogoIf you’ve read my previous article about how to enable automatic logins on CentOS 6, and it sounded a little daunting, you may be pleased to hear that it’s a little easier to accomplish the same thing on CentOS 7.1.

    If you’re using GNOME in a single user environment, and you’re confident that nobody else will use your system, you can enable auto-logins without the password questions like this:

    1. Login to GNOME as usual
    2. Find your name at the top right and click on it
    3. Now select Settings
    4. In the new window that opens, find Users
    5. Click on Unlock at the top right
    6. Select your own user and turn on Automatic Logins

    You need supervisor privileges to make this change. Next time you restart your system, you’re logged in automatically.

    Screen Shot 2015-08-13 at 10.19.12

    Thank you, CentOS!





     
  • Jay Versluis 4:35 pm on July 24, 2015 Permalink | Reply
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    Categories: Linux ( 70 )

    How to install Parallels Tools via the Command Line in CentOS 

    I like setting up barebones CentOS and other flavoured VMs on my Mac via Parallels Desktop. Trouble is, for such things like time synchronisation to work properly, something called Parallels Tools needs to be installed on each VM.

    This is to make sure Parallels Desktop can speak to the VM and communicate with it properly. It’s more important for GUIs so that the screen resolution and mouse handling is more accurate.

    Thing is, when you have a VM with a GUI, installing Parallels Tolls is extremely easy and may even happen automatically as soon as you install the OS. But if you have a command line only interface, it just doesn’t happen, and it’s up to us to install those tools manually. Here’s how to do it in CentOS 6.

    First, boot up your barebones VM and wait for it to start. Now head over to the VM’s menu and choose Actions – Install Parallels Tools. If they’re already installed, this message will change to “Reinstall Parallels Tools”.

    Screen_Shot_2015-07-21_at_16_39_13

    If your VM has a graphical user interface, this process will kick off the actual installation, but on barebones machines, it will merely attach the ISO image that contains the tools to your VM. In an ideal world, this tool would even mount the image for us, but sadly it doesn’t work with CentOS. Therefore we have a bit more work to do until we get to the installation part.

    You’ll see the following message to confirm the attachment:

    Screen-Shot-2015-07-21-at-16.29.35

    Now let’s login to our VM as root using our favourite SSH client (or simply use Parallels Desktop). We’ll create a directory to which we can mount the image. As suggested in the Parallels documentation, we’ll use /media/cdrom:

    mkdir /media/cdrom

    With this directory in place, let’s mount the ISO image to it so we can address it:

    mount -o exec /dev/cdrom /media/cdrom
    mount: block device /dev/sr0 is write-protected, mounting read-only

    The message is fairly self-explanatory: no writing to that ISO image. No problem! To start the installation, enter the directory and call the install script like so:

    cd /media/cdrom
    ./install

     

    Help! That’ didn’t work!

    Sometimes (in CentOS 7 for example) the ISO image isn’t properly mounted, and instead Parallels Desktop mounts a directory containing the ISO image. That’s no good of course. If you receive an error message along the lines of “command not found”, take a look at the CD Rom’s directory with the ls command.

    If there is no file called “install”, and instead there’s something like “prl-tools-lin.iso”, you need to manually attach the ISO image to your VM. To do this, restart your VM and select Devices – CD/DVD 1 – Connect Image. Now navigate to Applications – Parallels Desktop.app – Contents – Resources – Tools and pick the appropriate ISO file.

    Screen Shot 2015-08-07 at 12.49.50

     

    For all Linux flavours this is prl-tools-lin.iso. Once attached, mount the device as discussed above and you should be able to run the installer.

     

    Parallels Tools TUI in action

    The script will greet us with a TUI and some steps we need to complete, one of which may be that some additional components (such as make and gcc) need to be installed. That’s not always the case on barebones systems. Lucky for us, the script will take care of this for us too:

    Screen Shot 2015-07-21 at 16.33.51

    And that’s it! The script will finish fairly quickly, and at that point, Parallels Tools is installed in your VM. Congratulations! There’s only one final step: reboot the VM. You can either do that from the VM’s menu under Actions – Restart, or by issuing the following command:

    reboot now
    
    Broadcast message from root@yourserver
    (/dev/pts/0) at 16:53 ...
    
    The system is going down for reboot NOW!

    As soon as the VM is back up and running you’re all set :-)

    Screen Shot 2015-07-21 at 16.38.48

     

    Further Reading:





     
  • Jay Versluis 9:55 am on May 3, 2015 Permalink | Reply
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    Categories: Linux, Plesk ( 70 )

    How to update Plesk via the Command Line 

    Plesk-LogoYou can update Plesk via the Web Interface (under Tools and Settings – Updates and Upgrades). However sometimes the interface times out, or browsers get confused – therefore it’s good to know that you can apply updates via the command line interface as well. In this article I’ll show you how (in Linux – I don’t know much about running Plesk on Windows I’m afraid).

    We need to download the standard installer script for this. It’s a powerful little tool which can also be used to add or remove components from the current Plesk installation, or to install Plesk on a barebones server.

    As of 2015 the link can be found here:

    Screen Shot 2015-05-03 at 09.39.40

    If you click the option “Download Plesk installer for Linux”, you’ll see the actual script open in a new browser tab. Not what we want, although you could copy and paste this into a new file on your Linux system. Instead, right-click on the link and choose “Copy Link” instead.

    Screen Shot 2015-05-03 at 09.41.27

    With that link in your clipboard, connect to your server via SSH and download the file with something like wget:

    wget http://autoinstall.plesk.com/plesk-installer?long-url-here
    

    This will result in a file called “plesk-installer” with some nasty parameters at the end, several hundred characters in total. Let’s rename it to something easier and tweak the execution permissions:

    mv plesk-installer* plesk-installer
    chmod +x plesk-installer
    

    Now we can run the script like so:

    ./plesk-installer
    
    Welcome to the Parallels Installation and Upgrade Wizard!
    ===============================================================================
    
    This wizard will guide you through the installation or upgrade process. Before
    installing or upgrading Parallels products, be sure to back up your data.
    
    To start the installation or upgrade, press N and then press Enter.
    To quit the installer, press Q and then press Enter.
    

    Follow the instructions to upgrade Plesk. You can also call the script with several options, for a full list of those call it with “–help”. To see all available versions of Plesk during the installation, use “–all-versions”, which will eventually lead you to a screen similar to this:

    Select the desired products and their versions
    ===============================================================================
    
    The following product versions are available:
    
    1. [*] Parallels Plesk
      2. ( ) Parallels Plesk Panel 12.1.21 (testing)
      3. ( ) Parallels Plesk Panel 12.1.20 (testing)
      4. ( ) Parallels Plesk Panel 12.1.19 (testing)
      5. ( ) Parallels Plesk Panel 12.1.18 (testing)
      6. ( ) Parallels Plesk Panel 12.1.17 (testing)
      7. ( ) Parallels Plesk Panel 12.1.16 (testing)
      8. ( ) Parallels Plesk Panel 12.1.15 (testing)
      9. ( ) Parallels Plesk Panel 12.1.14 (testing)
      10. ( ) Parallels Plesk Panel 12.1.13 (testing)
      11. ( ) Parallels Plesk Panel 12.1.12 (testing)
      12. ( ) Parallels Plesk Panel 12.1.11 (testing)
      13. ( ) Parallels Plesk Panel 12.1.10 (testing)
      14. ( ) Parallels Plesk Panel 12.1.9 (testing)
      15. ( ) Parallels Plesk Panel 12.1.8 (testing)
      16. ( ) Parallels Plesk Panel 12.1.7 (testing)
      17. ( ) Parallels Plesk Panel 12.1.6 (testing)
      18. (*) Parallels Plesk 12.0.18 (Stable) (currently installed)
    
    N) Go to the next page; P) Go to the previous page; Q) Cancel installing
    To select a version, type the respective number;
    Select an action [N]: 
    

    If you call the script without any parameters, only micro updates and additional components are applied. Micro updates are usually applied automatically if this feature is enabled (it is by default).





     
  • Jay Versluis 4:05 pm on April 23, 2015 Permalink | Reply
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    Categories: Linux, Plesk ( 70 )

    How to open SMTP port 587 to send emails in Plesk 

    Plesk-LogoBy default Plesk on Linux uses Postfix for outgoing email, and by default listens on port 25 for outgoing SMTP mail. Some service providers do not allow to send emails on that port, and tragedy occurs: clients can’t send email with their Plesk servers. Not good.

    Other SMTP ports will usually work, such as the other favourite 587 – but by default, Postfix is not listening on this port for email submissions – at least not in Plesk 12.0.8 on CentOS 7.

    Here’s how to enable port 587 for such ventures:

    Open the Postfix configuration file at /etc/postfix/master.cf and find the following line. It’s commented out. All we have to do is to remove the hash in front of it, and email can be sent via port 587:

    submission inet n       -       n       -       -       smtpd
    

    Restart Postfix for the changes to take effect. In CentOS 5 and 6:

    service postfix restart
    

    This will also work in CentOS 7, but to be more precise:

    systemctl restart postfix.service
    

    Happiness!

    Note that port 587 needs to be open in your firewall. If the Plesk Firewall Extension is enabled, it’ll take care of it for you automagically.

     





     
  • Jay Versluis 6:03 pm on April 22, 2015 Permalink | Reply
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    Categories: Linux, Plesk ( 70 )

    How to turn off all Plesk Health Monitor alert emails 

    Plesk-LogoI have previously described how to adjust the values that the Plesk Health Monitor uses to determine when an email should be sent out.

    There is also a way to switch these emails off entirely. Here’s how:

    To turn off the daemon that is responsible for sending these emails, issue this:

    /etc/init.d/psa-health-monitor-notificationd stop
    

    No more emails until you restart the server, when the daemon will be resumed. If you don’t want that, switch it off at boot time using

    chkconfig psa-health-monitor-notificationd off
    

    To remove the Health Monitor altogether, head over to Tools and Settings – Updates and Upgrades and uninstall the component.





     
  • Jay Versluis 10:01 am on April 13, 2015 Permalink | Reply  
    Categories: Announcements, Linux ( 7 )

    LAMP Stack for Humans – now available on Amazon 

    Lampstack-SoftcoverMy new book LAMP Stack for Humans is now available on Amazon. It this 284 page guide I’ll walk you through the process of turning an old laptop into an always-on server. You can use it to run web applications in the comfort of your own home or office – no “cloud” required.

    Together we will configure the entire server: you will learn how to install CentOS, Apache, PHP and MySQL (or MariaDB) and WordPress. I will show you how you can reach your server from other computers on the network and how to create regular backups.

    Perfect for the Linux newbie and those who want to get started with web applications without spending money “in the cloud” (in my opinion THE WORST expression for describing remote computers).

    If you’re an avid reader of this site and have always wished that some instructions would be presented in a more cohesive form rather than in snippets, then LAMP Stack for Humans is perfect for you.

     

    Grab your free sample today, or read the entire book for free via Kindle Unlimited!

     





     
  • Jay Versluis 4:27 pm on April 9, 2015 Permalink | Reply
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    Categories: Linux ( 70 )

    How to edit your network connection settings from the command line in CentOS 7 

    CentOS 7 has a very funky text-based user interface that allows editing several important network connection settings. It’s called nmtui.

    Type the command without any parameters to get started:

    nmtui

    Now use this handy interface:

    Screen Shot 2015-04-09 at 16.22.13

    Screen Shot 2015-04-09 at 16.22.59

    Screen Shot 2015-04-09 at 16.22.33

    Your system may require a full restart for all settings to take affect.





     
  • Jay Versluis 12:36 am on March 25, 2015 Permalink | Reply  
    Categories: Linux ( 70 )

    How to find the UUID of a disk drive in Linux 

    There are two ways I know of which will print the UUID of all disk drives attached to the current system:

    blkid
    
    /dev/sr0: UUID="2014-12-02-19-30-23-00" LABEL="CDROM" TYPE="iso9660" 
    /dev/sda1: UUID="ae55a647-3c57-4ab5-9651-1389703fe6fe" TYPE="ext4" 
    /dev/sda2: UUID="bMtCfO-zpDU-7U1t-DcHg-Fe9p-Cy1K-Se0e1I" TYPE="LVM2_member" 
    /dev/sdb1: UUID="0982ce66-537a-497b-baaf-99136594f3e8" TYPE="ext4" 
    /dev/mapper/VolGroup-lv_swap: UUID="8f0652a8-d79b-453f-aa2d-0ff0b5d0ae7b" TYPE="swap" 
    /dev/mapper/VolGroup-lv_root: UUID="5afc1b25-e6cd-45b2-ad20-69f0fed323b9" TYPE="ext4" 
    /dev/mapper/VolGroup-lv_home: UUID="94e15e98-1cff-49a9-b76a-a8f3a948e2ea" TYPE="ext4" 
    

    or

    ls -la /dev/disk/by-uuid
    
    total 0
    drwxr-xr-x. 2 root root 160 Mar 25 00:24 .
    drwxr-xr-x. 5 root root 100 Mar 25 00:24 ..
    lrwxrwxrwx. 1 root root  10 Mar 25 00:24 0982ce66-537a-497b-baaf-99136594f3e8 -> ../../sdb1
    lrwxrwxrwx. 1 root root   9 Mar 25 00:24 2014-12-02-19-30-23-00 -> ../../sr0
    lrwxrwxrwx. 1 root root  10 Mar 25 00:24 5afc1b25-e6cd-45b2-ad20-69f0fed323b9 -> ../../dm-1
    lrwxrwxrwx. 1 root root  10 Mar 25 00:24 8f0652a8-d79b-453f-aa2d-0ff0b5d0ae7b -> ../../dm-0
    lrwxrwxrwx. 1 root root  10 Mar 25 00:24 94e15e98-1cff-49a9-b76a-a8f3a948e2ea -> ../../dm-2
    lrwxrwxrwx. 1 root root  10 Mar 25 00:24 ae55a647-3c57-4ab5-9651-1389703fe6fe -> ../../sda1
    

    The UUID is required to permanently mount specific disk drives in /etc/fstab.





     
  • Jay Versluis 8:45 am on March 7, 2015 Permalink | Reply
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    Categories: Linux ( 70 )

    How to specify FTP credentials in command line scripts 

    It’s easy to establish an FTP connection using the ftp command from the Linux Command Line. Sadly this command does not accept login credentials as parameters – which means that if we use it in a script, our script will pause and wait for us to type those credentials in manually. Not really suitable for automated backups.

    Thanks to a clever mechanism called netrc we can create a file in the home directory of the user who runs the script and provide credentials there. Let me show you how this works.

    First we create a file called .netrc. It’s a hidden file and it needs to reside in the home directory of the user who will connect via FTP. I’m going to use root for this:

    vi ~/.netrc
    
    # machine  login  password 
    machine ftp.domain.com login yourusername password yourpassword
    

    The first line is just a comment to you can remember how to add parameters here. The second line is an example of a host you want to connect to. Add as many other servers as you like, all following the same pattern.

    Be aware that you need to connect to the server as it is specified in the .netrc file. In the above example, if you would connect to domain.com instead, you would be asked for credentials as netrc cannot find a match.

    The .netrc file needs to be readable only by this one user, otherwise connections may fail. We do this by changing the file permissions to 600:

    chmod 600 ~/.netrc
    

    That should do it! Try to connect with

    ftp ftp.domain.com
    

    and the connection will be established without the prompt for credentials.

    If netrc isn’t working for you, or you choose not to use it, note that you can also provide FTP credentials with a here script. I find that approach a bit clunky, but the following link has details on how to do that:





     
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