TOPIC: LINUX DISTRIBUTIONS
Three handy Linux commands, one each for navigation, system Information and upgrades
8th July 2015
Here are some Linux commands that I encountered in a feature article in the current issue of Linux User & Developer that I had not met before:
cd -
This returns you to the previous directory where you were before with having to go back through the folder hierarchy to get there and is handy if you are jumping around a file system and any other means is far from speedy.
lsb_release -a
It can be useful to uncover what version of a distro you have from the command line and the above works for distros as diverse as Linux Mint, Debian, Fedora (it automatically installs in Fedora 22 if it is not installed already, a more advanced approach than showing you the command like in Linux Mint or Ubuntu), openSUSE and Manjaro. These days, the version may not change too often, but it still is good to uncover what you have.
yum install fedora-upgrade
This one can be run either with sudo or in a root session started with su and it is specific to Fedora. The command performs an upgrade of the Fedora distro itself, and I wonder if the functionality has been ported to the dnf command that has taken over from yum. My experiences with that in Fedora 22 so far suggest that it should be the case, though I need to check that further with the VirtualBox VM that I have created.
Controlling clearance of /tmp on Linux systems
19th June 2015
While some may view the behaviour in a less favourable, I always have liked the way that Linux can clear its /tmp directory every time the system is restarted. The setting for this is in /etc/default/rcS and the associated line looks something like:
TMPTIME=0
The value of 0 means that the directory is flushed completely every time the system is restarted, but there are other options. A setting of -1 makes the directory behave like any other one on the system, where any file deletions are manual affairs. Using other positive integer values like 7 will specify the number of days that a file can stay in /tmp before it is removed.
What brought me to this topic was the observation that my main Linux Mint system was accumulating files in /tmp and the cause was the commenting out of the TMPTIME=0 line in /etc/default/rcS. This is not the case on Ubuntu, and using that is how I got accustomed to automatic file removal from /tmp in the first place.
All of this discussion so far has pertained to PC's where systems are turned off or restarted regularly. Things are different for servers of course and I have seen tools like tmpreaper and tmpwatch being given a mention. As if to prove that there is more than one way to do anything on Linux, shell scripting and cron remain an ever present fallback.
Restoring GRUB for dual booting of Linux and Windows
11th April 2015
Once you end up with Windows overwriting your master boot record (MBR), you have lost the ability to use GRUB. Therefore, it would be handy to get it back if you want to start up Linux again. Though the loss of GRUB from the MBR was a deliberate act of mine, I knew that I'd have to restore GRUB to get Linux working again. So, I have been addressing the situation with a Live DVD for the likes of Ubuntu or Linux Mint. Once one of those had loaded its copy of the distribution, issuing the following command in a terminal session gets things back again:
sudo grub-install --root-directory=/media/0d104aff-ec8c-44c8-b811-92b993823444 /dev/sda
When there were error messages, I tried this one to see if I could get additional information:
sudo grub-install --root-directory=/media/0d104aff-ec8c-44c8-b811-92b993823444 /dev/sda --recheck
Also, it is possible to mount a partition on the boot drive and use that in the command to restore GRUB. Here is the required combination:
sudo mount /dev/sda1 /mnt
sudo grub-install --root-directory=/mnt /dev/sda
Either of these will get GRUB working without a hitch, and they are far more snappy than downloading Boot-Repair and using that; I was doing that for a while until a feature on triple booting appeared in an issue of Linux User & Developer that reminded me of the more readily available option. Once, there was a need to manually add an entry for Windows 7 to the GRUB menu too and, with that instated, I was able to dual-boot Ubuntu and Windows using GRUB to select which one was to start for me. Since then, I have been able to dual boot Linux Mint and Windows 8.1, with GRUB finding the latter all by itself. Since your experiences too may show this variation, it's worth bearing in mind.
Turning off Apport crash reporting on Ubuntu
6th April 2015
Last week, I kept getting a multitude of messages from Ubuntu's crash reporting tool, Apport. So many would appear at once on reaching the desktop session during system start-up that I actually downloaded an installation ISO disk image intending to perform a fresh installation to rid myself of the problem. In the end, it never came to that because another remedy produced the result that I needed.
Emptying /etc/crash was a start, but it did not do what I needed, and I disabled Apport altogether. This meant editing its configuration file, which is named apport and is found in /etc/default/. The following command should open it up in Gedit on supplying your password:
gksudo gedit /etc/default/apport
With the file opened, look for the line with enabled=1 and change this to enabled=0. Once that is done, restart Apport as follows:
sudo restart apport
This will need your account password before working, with any messages appearing afterwards. While I would not have done this for a real system problem, my Ubuntu GNOME installation was working smoothly, so it was the remedy I needed. The tool lets Ubuntu developers get information about application crashes, but it sends me to the Ubuntu Launchpad bug reporting website, which requires login details. This is enough to stop me continuing, making me wonder if developers could get what they need without this extra manual step. This would provide them with additional information and give us a more stable operating system in return.
Toggling the appearance or non-appearance of the Firefox session exit dialogue box
22nd March 2015
One thing that I notice with Firefox installations in both Ubuntu and Linux Mint is that a dialogue box appears when closing down the web browser asking whether to save the open session or if you want to have a fresh session the next time that you start it up. Initially, I was always in the latter camp, but there are times when I took advantage of that session saving feature for retaining any extra tabs containing websites to which I intend to return or editor sessions for any blog posts that I am still writing; sometimes, composing the latter can take a while.
To see where this setting is located, you need to open a new tab and type about:config in the browser's address bar. This leads to advanced browser settings, so you need to click OK, answering a warning message, before proceeding. Then, start looking for browser.showQuitWarning using the Search bar; it acts like a dynamic filter on screen entries until you get what you need. On Ubuntu and Linux Mint, the value is set to true but false is the default elsewhere; unlike Opera, Firefox generally does not save sessions by fault unless you tell it to that (at least, that has been my experience anyway). Setting true to false or vice versa will control the appearance or non-appearance of the dialogue box at browser session closure time.
Automatically enabling your network connection at startup on CentOS 7
15th August 2014
CentOS 7's release sparked my curiosity, so I tried it in a VirtualBox virtual machine. It uses GNOME Shell in classic mode, making it feel similar to GNOME 2. One thing to note is that it requires at least VirtualBox version 4.3.14, or the Guest Additions kernel drivers won't compile. This might seem surprising when you learn it uses kernel version 3.10.x and GNOME Shell 3.8.4. Like Debian production releases, CentOS chooses established versions for stability, fitting its enterprise-focused user base. Despite this conservative approach, it still looks good, though trying to change the desktop background froze the machine. Otherwise, most things work well.
However, there are surprises, including one I noticed: network connectivity needed switching on every time the VM started. This occurs with the default installation and has been a known issue since at least CentOS 6. It's not difficult to fix once you know how.
What you need to do is look for the relevant configuration file in /etc/sysconfig/network-scripts/ and update that. Using the ifconfig command, I found that the name of the network interface. Usually, this is something like eth0, but it was enp0s3 in my case, so I had to look for a file named ifcfg-enp0s3 and edit that. The text that is sought is ONBOOT=no and that needs to become ONBOOT=yes for network connections to start automatically. To do something similar from the command line, CentOS had suggested the following:
sed -i -e 's@^ONBOOT="no@ONBOOT="yes@' ifcfg-enp0s3
This uses sed for an inline (and case-insensitive) edit of the file to change 'no' to 'yes' after accessing the /etc/sysconfig/network-scripts/ directory. I edited manually with Gedit, which also works. Note that file editing needs superuser privileges, so switch to root with the su command or use sudo.
Suppressing Update Notifier messages in Ubuntu GNOME 14.04
18th July 2014
Even though I use only the command line for system updates, I still received system restart messages after kernel updates. Though these can be helpful, I prefer to restart my system on my own schedule, especially when running processes I don't want to interrupt.
In Ubuntu GNOME 13.10 and earlier, these messages didn't appear. I wanted to return to a notification-free experience. The Update Notifier application causes these messages, but removing it significantly impacts the system, making that approach impractical.
The application starts automatically at boot but doesn't appear in Startup Applications Preferences (launched via gnome-session-properties). This is because the NoDisplay flag in its autostart shortcut located in /etc/xdg/autostart/ is set to true. To make it visible, you need to set this flag to false.
The following command will reveal all hidden startup applications (note that the command is split across two lines for display purposes, and you may need to adjust quotes when executing it):
sudo sed -i 's/NoDisplay=true/NoDisplay=false/g'
/etc/xdg/autostart/*.desktop
The sed command changes NoDisplay=true to NoDisplay=false in all desktop files, revealing hidden entries in Startup Applications Preferences. This allows you to disable the Update Notifier. While deleting the desktop file would be more permanent, this solution works well as it stops restart notifications. Since I regularly update my system and shut down daily, updates are applied automatically, and everything functions properly.
Dropping back to a full screen terminal session from a desktop one in Linux
29th May 2014
There are times when you might need to access a full screen terminal from a Linux graphical desktop. For example, I have needed this when installing Nvidia's graphics drivers on Ubuntu or Linux Mint. Another instance occurred on Arch Linux when a Cinnamon desktop update prevented me from opening a terminal window. The full screen command let me install an alternative terminal emulator, with Tech Drive-in's list proving helpful. Similar issues might need fixing on FreeBSD installations. These latter examples happened within VirtualBox, which has special requirements for accessing full screen command line sessions, which I'll explain later.
When running Linux on a physical PC, press CTRL + ALT + F1 to enter a full screen terminal and CTRL + ALT + F7 to return to the graphical desktop. In a Linux VirtualBox guest with a Linux host, these shortcuts affect the host instead. For the guest OS, use [Host Key] + F1 to enter a full screen terminal and [Host Key] + F7 to return to the graphical desktop. The default Host Key is the right CTRL key, unless you've changed it.
X sessions in GNOME and Cinnamon desktop environments support this functionality, but I can't confirm it works with alternatives like Wayland. Hopefully, this feature extends to other setups, as terminal sessions are occasionally needed for system recovery. Such mishaps are thankfully rare and should be virtually non-existent for most users.
Fixing garbled background images in GNOME Shell after upgrading to Ubuntu GNOME 14.04
2nd May 2014
On upgrading from Ubuntu GNOME 13.10 to Ubuntu GNOME 14.04, a few rough edges were to be noticed. One was the display of my chosen background image: it was garbled. Later, I discovered that there is a maximum width of 2560 px for background images in GNOME Shell these days and that things get messy beyond that.
In my case, the image width was around 6000 px, and I was used to it getting resized in GNOME Shell 3.8 and its predecessors. It appears that the functionality got removed after that, though, so the workaround of manual image resizing in the GIMP needed to be employed. Though having big images open in memory creates an additional overhead, not handling them very well at all looks like a bug caused by setting 2560 px as a maximum screen width for the GNOME Shell panel and the complete removal of Nautilus from desktop rendering duties. Let's hope that sense is seen with ever larger screen sizes and resolutions coming our way.
It's the sort of thing that did get me looking at adding on Cinnamon 2.2 for a while before setting background image scaling using the indispensable GNOME Tweak Tool was discovered. LinuxG.net has a useful tutorial on this for anyone with such an adventurous streak in them. For now though, I am OK with my set-up, but the GNOME project's focus on minimalism could affect us in other ways, so I can see why Clem Lefebvre started the Cinnamon one primarily for Linux Mint and the desktop environment is appearing elsewhere too. After all, Gedit lost its menu bar in GNOME 3.12 so it's just as well that we have alternatives.
Update 2014-05-06: It appears that the desktop image bug that afflicts GNOME Shell 3.10 got sorted for GNOME Shell 3.12. At least, that is the impression that an Antergos instance in a VirtualBox virtual machine gives me.
ERROR: Can't find the archive-keyring
10th April 2014
When I recently did my usual system update for the stable version Ubuntu GNOME, there were some updates pertaining to apt and the process failed when I executed the following command:
sudo apt-get upgrade
Usefully, some messages were issued and here's a flavour:
Setting up apt (0.9.9.1~ubuntu3.1) ...
ERROR: Can't find the archive-keyring
Is the ubuntu-keyring package installed?
dpkg: error processing apt (--configure):
subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
apt
E: Sub-process /usr/bin/dpkg returned an error code (1)
Web searches indicated the issue was missing files in /usr/share/keyring, which I didn't delete. Since apt was disabled due to the missing keyring files, installing software for fixes was impossible. My solution was to copy the /usr/share/keyring files from an Ubuntu GNOME 14.04 virtual machine to the same location on my Ubuntu GNOME 13.10 host. For others without this setup, I've included these files in a zip file below. While other solutions like Y PPA were mentioned, they required prior installation, making them useless when tools like Synaptic were unavailable. I'd appreciate information on other fixes that don't involve reinstalling the operating system, potential causes for the file loss, and how to prevent it.