net.ipv6.conf.default.use_tempaddr = 2
For years, I’ve been using Terminus as my day-to-day programming and terminal font. It’s a well-known pixmap font, which makes it crisp and clear at the sizes it was designed for. I was using it in 16 pixels.
My genetic background, however, and years of spending hours in front of a computer screen have taken a small toll on my eyesight, so a few months ago I decided I needed a bigger font. In my opinion, however, Terminus looks too thin as it not that easy to read in sizes beyond 16 pixels. I needed something a bit thicker but readable.
As part of my search for a new font, I also switched from xterm to gnome-terminal. gnome-terminal is pretty simple to use and carried a very small list of additional dependencies that needed to be installed in my already-running system. At the same time, it supported Freetype and I could use a wider variety of fonts.
I evaluated DejaVu Sans Mono, Droid Sans Mono, Fira Mono, Source Code Pro and Ubuntu Mono, and I stayed with Ubuntu Mono. I’ve been using it for two months already and it’s very comfortable and easy to read.
The most frequent complaint about the font is that its “round” design and appearance make it look a bit too informal and, indeed, its style sometimes reminds me of the much-criticized Comic Sans font. It was only after I read a bit about it on Wikipedia that I learned its designers include Vincent Connare, the Comic Sans creator. Those aspects would be important if I was using the font as part of a professional document or to convey information to others, but I’m using it on my own screen. Its simple features show off when using the font in a low-resolution computer screen. In higher DPIs and sizes, the font is not as pretty as some of the competitors I mentioned above.
As a matter of fact, a few months ago I also had to choose a monospace font for a large decorative “Hello, World” sign and I chose DejaVu Sans Mono, which looks great, modern and serious if you can display the shape of its glyphs in detail.
DejaVu Sans Mono and Droid Sans Mono also look pretty good on screen for the resolution and size I was aiming for.
Fira Mono and Source Code Pro were disappointing, however. I love their proportional sans serif counterparts, Fira Sans and Source Sans Pro, but the monospaced variants have several drawbacks. Fira Mono has a serious problem in its lowercase R glyph. The whole font is sans serif but somehow the lowercase R turned out to be serif-esque. In addition, its at and ampersand signs have unusual and distracting designs, and those come up on the screen often while programming or on the command line. Source Code Pro looks nice in lower resolutions, like Terminus, but its glyphs are a bit too simple as soon as you increase the font size and, more importantly, it’s the widest font of the ones I tried, and it’s not able to fit as many columns of text in the same width as its competitors. By comparison, all other fonts feel more “square” without being too compact.
Many people won’t try Ubuntu Mono because it has “Ubuntu” in its name and for a variety of other reasons. It’s a bit too informal and smaller than other fonts (I normally increase the font size a bit to fit a similar number of characters on the screen compared to other fonts). In any case, its characters have simple shapes, like Terminus does, and are easy to tell apart and read. It can be used for hours and you won’t get tired of it. If you haven’t tried it, I recommend you give it a shot.
Some days ago I tweeted my ISP router was assigning me a working public IPv6 address. I don’t know how long it had been that way when I wrote the tweet, but my guess is less than a week. I normally update a few personal repositories each Sunday and push changes in them to Bitbucket. That Sunday, while pushing, I noticed git was adding a few IPv6 addresses to my known_hosts file, which hadn’t happened the Sunday before.
Millions of people are already using IPv6 to access the Internet from their phones and computers, but this is significant because IPv6 adoption in Spain is lagging behind most other countries in Western Europe. My current ISP, Orange Spain, is one of the big players and it’s probably leading IPv6 adoption by number of users, as it’s been deploying it to more and more FTTH clients recently. I don’t know if there’s been a big transition lately or if they’re slowly proceeding by regions.
Obviously, I’m not trying to “sell you” Orange. It’s hated by many and adored by others. In my case it’s doing a good job. I have no complaints so far. I had to call for technical assistance once and they responded properly and fast but your mileage may vary. In any case, I think it’s important to give them (or anyone else) some credit when they do something well, like expanding IPv6 adoption.
Since the day I discovered I was using IPv6, I’ve been reading a bit about it and adjusting my systems and home network to the new situation.
The first topic I read about was how IPv6 addresses worked and the way they are assigned. The best reference I found, as usual, is Wikipedia’s article on IPv6 addresses, and in particular the section about the IPv6 address space and its allocation policies.
Then, I headed to a few IPv6 test pages to see if my IPv6 setup was working properly or if I was to expect problems in some areas. There are quite a few interesting IPv6 test pages, like the one from Google, which is very simple but trustworthy at the same time. There’s also the classic IPv6 test page from Jason Fesler, which reported a score of 10/10. However, I also found an interesting test at ipv6-test.com which warned me I was using SLAAC without privacy extensions.
I didn’t have any idea about what that meant, so I read a bit more about it. It turns out there are 3 normal ways a computer can get an IPv6 address. The first one is static assignment, like in IPv4. The second one is DHCPv6, which is similar to normal DHCP. The third one achieves the same but it’s a “native” standardized mechanism called SLAAC.
IPv6 requires all network interfaces to have a link-local address in addition to other IPv6 addresses they may have. With IPv6 it’s a given a network interface will have multiple addresses assigned. This link-local address starts with prefix “fe80”. Link-local addresses are very similar in concept to both the Ethernet MAC address (and in Ethernet interfaces it’s usually derived from it) and a local IPv4 address. The difference with the latter is link-local addresses are not routable.
Imagine your computer has two network interfaces. The first one has a link-local address with value fe80::1, and the second one has fe80::2. You have a second computer connected with a network cable to one of those interfaces, and its link-local address is fe80::3. If you try to contact fe80::3 (e.g. by trying to SSH into it), which one should be the outgoing interface and your local address in those packets? You don’t know. Fortunately, while not recommended, a lot of software out there lets you use link-local addresses to contact other computers by appending a percent sign and the name of the network interface you want to go out from, like fe80::3%enp3s0 (if enp3s0 is the name of the network interface you want to use to reach that address).
But I digress. Link-local addresses are also used to be able to send IPv6 packets from network interfaces automatically without having another, possibly public, address assigned yet. Using these link-local addresses, you can use SLAAC to send router solicitation requests and routers in your link neighborhood may reply with a prefix assignment you can use to create an additional globally routable address for your interface. At this point you’d normally have two IPv6 addresses assigned to your network interface: link-local and global.
Normally, routers assign a /64 prefix to your computer, and your computer fills the last remaining 64 bits in the address with something derived from the Ethernet MAC address. This is a privacy problem in today’s Internet. Because the way the last 64 bits are derived from the Ethernet MAC address, it’s possible for anyone to identify you and track you across ISPs, connections and services, without using HTTP cookies and without effort.
Enter Privacy Extensions. With them, the Ethernet MAC address will not be used to fill the remaining 64 bits in your assigned prefix to create the IPv6 address. It will be random and it will change every time the network interface is brought up, requesting an IPv6 prefix to the router.
In many Linux distributions this mechanism is not activated by default. At least in my Fedora installation, it was not. It should probably be used in most home desktops, laptops, phones and workstations.
The easiest way to use Privacy Extensions in Linux is by writing “2” to
/proc/sys/net/ipv6/conf/default/use_tempaddr. This is normally achieved at
boot time before the network interface is brought up by saving the following
/etc/sysctl.conf or a new file in
sysctl.d is probably the best mechanism if your distribution allows it because your settings will survive system upgrades without having to manually merge file contents.
According to the Linux kernel documentation, a value of 0 disables Privacy Extensions, a value of 1 enables Privacy Extensions but prefers public addresses to temporary addresses. A value greater than 1 enables Privacy Extensions and gives preference to the temporary address when creating connections. Hence using 2 as the value.
After enabling these Privacy Extensions, you’ll notice your public address doesn’t disappear from the interface. Instead, a third IPv6 address is added to it and used by default.
If you let NetworkManager handle your IPv6 settings, it will interfere and probably ignore the sysctl parameter above. In any case, I think it’s useful to have it there as a fallback. If you tell NetworkManager to ignore the IPv6 part of your connection, the sysctl parameter will kick in. Otherwise, the easiest way to achieve the same effect is using a GUI like nm-connection-editor and setting “IPv6 privacy extensions” to “Enabled (prefer temporary address)” and “IPv6 address generation mode” to “EUI64”, but you could also set the latter to “Stable privacy” and neither public address would be derived from the Ethernet MAC address, with one being temporary and another one being stable.
Most Android phones have Privacy Extensions enabled. If your home network has WiFi access and your phone uses it, you can make sure Privacy Extensions are enabled by visiting ipv6-test.com from it, but you can also check if your phone has 3 different IPv6 addresses in Settings > About phone > Status > IP address.
I also made some small adjustments to other settings, like using IPv6 DNS servers by default. Both Cloudflare’s 220.127.116.11/18.104.22.168 and Google’s 22.214.171.124/126.96.36.199 public DNS servers have IPv6 counterparts you can use.
I could talk about a few more details but this post is long enough already, so I can only wrap it up by saying I’m really happy to see IPv6 adoption expanding in Spain and being part of it. At the same time I’m surprised at how seamless and transparent the transition to IPv6 is being for many people all over the world, so congratulations to all those sysadmins and engineers behind it.
Although the upgrade to Fedora 29 was smooth as silk, as I mentioned in a previous post, I quickly noticed my system was taking slightly longer to give me the virtual terminal login prompt when booting up. Linux in general and Fedora in particular has always booted really fast for me, specially after switching to SSD drives some years ago. After a cold boot, I get the login prompt in less than 5 seconds from the Grub menu, so a few extra seconds are easily noticed.
To give you a bit of background information, I’m the kind of person that boots to a virtual terminal by default instead of a graphical login prompt, and I use the “text” plymouth theme. Normally, just after logging in, I go ahead and type “xs”, which is a fast alias I have to launch an X session using “startx” with a few parameters, which in turn ends up launching i3. But booting to a virtual terminal is very handy when I need to exit the X session in order to uninstall the proprietary NVIDIA drivers to upgrade an X11 package, mesa or the kernel. It’s also a bit faster when I don’t need to launch an X session for a basic task I want to do quickly. The inconvenience of having to type x+s+Enter after logging in is tiny, because it takes a fraction of a second to perform those 3 keystrokes, and my hands are already at the keyboard after typing my user password.
After experimenting a bit and measuring actual boot time with a chronometer, I
verified my findings. Indeed, it was taking a bit over 9 seconds to get to the
login prompt, which is at least twice as long as what I was used to. After
analyzing the boot process with systemd-analyze and doing various experiments, I
booted with systemd’s log level set to “debug” and I was finally able to
verify what was happening. The prompt is given by the
[email protected] unit, and
it was taking 5 seconds to launch “agetty” after the unit was considered
started. See the following boot log:
Nov 06 22:49:57 localhost.localdomain systemd: [email protected]: Passing 0 fds to service Nov 06 22:49:57 localhost.localdomain systemd: [email protected]: About to execute: /sbin/agetty -o '-p -- \u' --noclear tty1 $TERM Nov 06 22:49:57 localhost.localdomain systemd: [email protected]: Forked /sbin/agetty as 613 Nov 06 22:49:57 localhost.localdomain systemd: [email protected]: Changed dead -> running Nov 06 22:49:57 localhost.localdomain systemd: [email protected]: Job [email protected]/start finished, result=done Nov 06 22:49:57 localhost.localdomain systemd: Started Getty on tty1. Nov 06 22:49:57 localhost.localdomain audit: SERVICE_START pid=1 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:init_t:s0 msg='[email protected] comm="systemd" exe="/usr/lib/systemd/systemd" hostname=? addr=? terminal=? res=success' [Thousands of lines...] Nov 06 22:50:02 localhost.localdomain systemd: [email protected]: Executing: /sbin/agetty -o '-p -- \u' --noclear tty1 linux
That appeared to be the exact cause of my login prompt delay, but I wasn’t sure
about why it was happening. However, a few web searches later I arrived to the
conclusion it was due to the
[email protected] unit being declared with
Type=idle. According to
Behavior of idle is very similar to simple; however, actual execution of the service program is delayed until all active jobs are dispatched. This may be used to avoid interleaving of output of shell services with the status output on the console. Note that this type is useful only to improve console output, it is not useful as a general unit ordering tool, and the effect of this service type is subject to a 5s time-out, after which the service program is invoked anyway.
Indeed, changing the unit to type “simple” restored the old behavior. I’ve
investigated a bit and that unit has had that type for a long time, so my guess
is the change I observed in boot time has been triggered by other changes in the
Fedora boot process. Just for completeness, this is the list of units with type
“idle” in my system, but the only one that matters to me is
/usr/lib/systemd/system/[email protected]:30:Type=idle /usr/lib/systemd/system/emergency.service:24:Type=idle /usr/lib/systemd/system/rescue.service:23:Type=idle /usr/lib/systemd/system/[email protected]:35:Type=idle /usr/lib/systemd/system/[email protected]:40:Type=idle /usr/lib/systemd/system/console-getty.service:25:Type=idle
It’s worth noting I don’t get text garbage on screen by changing the unit type to simple, at least in Fedora. First of all, the wait process was timing out in any case, so I could still get a garbaged prompt. Furthermore, when agetty is launched, plymouth seems to go away and I get a clean login prompt. Waiting for an idle system is futile, more so if the system boots slower than mine. Those reasons prompted me to file a bug report that hasn’t been updated since filed. Fedora’s systemd package has 146 open bugs as of the time I’m writing this and many of them are sitting there marked as “New” without being confirmed or assigned.
To change the unit type to “simple” in a non-intrusive way that survives system upgrades, the best way is to create a so-called drop-in file for it. As root, use:
systemctl edit [email protected]
That will launch a text editor and create a file named
/etc/systemd/system/[email protected]/override.conf where you can change parts
of the unit configuration. The contents should simply be:
If you also boot to a virtual terminal, I hope this helps or at least encourages you to experiment a bit to see if you can boot faster.
Almost two years ago I wrote about a nice surprise in the Fedora freetype package that made it easy for users to rebuild the package and include subpixel rendering support. In the original article I also added some brief instructions with a few commands to run in order to create and prepare a specific user account used to build packages.
Expanding on that, I mentioned you’d want to install the build dependencies for
the freetype package before rebuilding it. Back then I mentioned the packages
explicitly. The list can be obtained from the package SPEC file, but there’s a
better option. Any time you want to rebuild an official package you can install
its build dependencies automatically by using
dnf builddep, as in:
dnf builddep freetype
Furthermore, if you rebuild an official package you’ll notice sometimes Fedora wants to reinstall the original one from the official repositories. In order to avoid that, you can create a local repository containing your own packages and make it take precedence over the official packages. In any case, this is also handy if you have additional non-official packages you build yourself.
The first step is creating the repository metadata. Let’s suppose the build user
is named “build”, and let’s suppose rpmdevtools has been set up normally for
that user, creating a bunch of directories under
One of those is the directory containing RPM files for every package you create,
/home/build/rpmbuild/RPMS. It has one subdirectory for each
architecture you create packages for, normally
x86_64 and sometimes
too. You want to create a repository with the contents of that directory. It
could hardly be easier:
You can run that as the build user. It will create a subdirectory called
repodata containing package metainformation. If you have a lot of personal
packages or if you want something faster, you can replace
createrepo_c, a version of
createrepo written in C that’s supposed to be
much faster. For my simple use case, I barely notice any difference between the
two. You’ll have to run that command every time you add or remove packages from
the repository, to update their metainformation.
The final step is telling dnf there’s a repository there. That’s as easy as
creating a file under
/etc/yum.repos.d with information about it. I called
localrepo.repo and it has the following contents:
[localrepo] name=localrepo baseurl=file:///home/build/rpmbuild/RPMS enabled=1 gpgcheck=0 metadata_expire=60s priority=80
The base URL mentions the path to the local directory. The repo is also enabled
and its packages are not signed, so the GPG check is disabled. Metadata expires
after 60 seconds and needs to be rechecked then. That’s handy so you won’t have
to use dnf’s
--refresh option all the time while working with your local
repository. The last line contains a numeric priority value.
The lower the number, the higher the priority. The default priority is 99
dnf.conf(5) and that’s the priority of the official repos because
they don’t set a value. If you use other non-official repositories like RPM
Fusion, you’ll see they have their own priority value. You have to decide if you
want your local repo to have higher or lower priority compared to others and put
a numeric value there.
Going back to the rebuilt freetype package, dnf won’t insist anymore on reinstalling the official version, but it will update it if the official package version is considered more recent. Hopefully, you’ll notice font rendering has changed slightly, rebuild the package and reinstall it from your local repository.
I upgraded to Fedora 29 yesterday without any issues. The upgrade process was as flawless as the last few ones so I have to congratulate everyone involved once more for doing a superb job.
When I switched from Slackware to Fedora almost four years ago I mentioned it was probably as future-proof as Debian, the other option I had been considering. The recent acquisition of Red Hat by IBM has many people worried for several reasons, even if most people prefer to be prudent and wait to see how things turn out.
Fedora could be affected but, more importantly, Red Hat’s numerous contributions to a myriad of projects could be affected too. Kernel, GCC, glibc, Gnome, GTK, etc. It’s obvious if this operation doesn’t work it will have side effects on the whole Linux ecosystem, so it’s not a matter of just switching distributions.
In any case, if Fedora ceased to exist my next option would be Debian unstable. Almost four years ago I mentioned Debian testing, but I’ve been reading a bit on the difference between the two and I would probably prefer unstable now. My second option would be Ubuntu. It’s based on Debian unstable but it has a release schedule similar to the one Fedora has so it would be familiar to me at this point.