After upgrading to Ubuntu 16.04, the font in my GNOME is a mess (again). So I spent another afternoon trying to figure out how to choose the fonts I need using fontconfig.

My goal is to use two fonts, an English one for displaying generic characters, and a Chinese one for, um, Chinese. Although I can use a single Chinese font for both, but the English characters displayed in Chinese font is disastrous. So basically I want to tell fontconfig to use the two fonts in a preferred order: Use English one wherever possible, and fallback to the native one when the former can’t do the job.

Actually I have solved this before, but I forgot what I did back then. So I had to spend another afternoon Googling and reading their long and non-standardized docs on how to express my request in their weird XML tags. After several attempts, I found that the following configuration works just fine.

The whole XML below should be saved as ~/.config/fontconfig/conf.d/99-xiaodu.conf (create non-existent folders when needed), which is the preferred location for user-specific fontconfig files.

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>
  <!-- For other languages -->
  <match target="pattern">
    <test qual="any" name="family">
     <string>sans-serif</string>
   </test>
   <edit name="family" mode="prepend" binding="strong">
      <string>Arial</string>
    </edit>
 </match>
  <match target="pattern">
    <test qual="any" name="family">
     <string>serif</string>
    </test>
   <edit name="family" mode="prepend" binding="strong">
      <string>Times New Roman</string>
    </edit>
 </match>
  <match target="pattern">
    <test qual="any" name="family">
     <string>monospace</string>
    </test>
   <edit name="family" mode="prepend" binding="strong">
      <string>Inconsolata</string>
    </edit>
 </match>
  <!-- For Chinese -->
  <match target="pattern">
    <test name="lang">
      <string>zh-cn</string>
    </test>
   <test qual="any" name="family">
     <string>sans-serif</string>
   </test>
   <edit name="family" mode="prepend" binding="strong">
      <string>Arial</string>
      <string>Source Han Sans CN</string>
   </edit>
 </match>
  <match target="pattern">
    <test name="lang">
      <string>zh-cn</string>
    </test>
   <test qual="any" name="family">
     <string>serif</string>
    </test>
   <edit name="family" mode="prepend" binding="strong">
      <string>Times New Roman</string>
      <string>Simsun</string>
   </edit>
 </match>
  <match target="pattern">
    <test name="lang">
      <string>zh-cn</string>
    </test>
   <test qual="any" name="family">
     <string>monospace</string>
    </test>
   <edit name="family" mode="prepend" binding="strong">
      <string>Inconsolata</string>
      <string>Source Han Sans CN</string>
   </edit>
 </match>

</fontconfig>

Basically this file tells fontconfig, when the locale is zh-cn (Chinese), it should to prepend the two fonts (English and Chinese) to the matching list; otherwise just prepend the English one.

Notice that the first font in each <edit> block is the English font, where the second is the native font. You should replace the language code (RFC3066 style) and all six font names using your favorite text editor, with respect to the fonts’ types (sans, serif or mono). If you want to test your work, use fc-match with something like $ LANG=zh-CN fc-match -s sans | head -2.

I just hope one day there would be a nice GUI for all this crap.

中文摘要：这篇文章介绍如何在 Ubuntu 中通过配置 fontconfig 同时选择要使用的英文和中文字体，使用英文字体显示一般字符，中文字体显示中文字符。

This article shows how to prevent a certain package from being installed, manually or as a dependency, on Linux systems using apt (apt-get) like Ubuntu and Debian.
这篇文章介绍如何在使用 apt (apt-get) 的系统上（例如 Ubuntu 和 Debian），防止某个软件包被安装，包括手动或被依赖。

It utilizes the “pinning” feature of apt, which you can read about in detail with man apt_preferences .
使用的原理是 apt 的 “pinning” 功能，可以通过 man apt_preferences 获取详细文档。

1. Say we want to block “ttf-mscorefonts-installer” from being installed, which is a recommended dependency of “ubuntu-restricted-extras”. When we use apt-get install ubuntu-restricted-extras , the package will be automatically installed. If we use the “–no-install-recommends” switch, many other packages will be ignored, but we just want to block that one specific package.
   假设我们不想安装 “ttf-mscorefonts-installer” 软件包，但它是 “ubuntu-restricted-extras” 的推荐依赖。如果我们使用 apt-get install ubuntu-restricted-extras 命令，则依赖软件包也会自动安装。我们可以用 “–no-install-recommends” 开关阻止推荐依赖，但是同时会阻止其它很多软件包。接下来的方法适用于只阻止特定的一个软件包。
2. In the folder “/etc/apt/preferences.d” we create a plain text file “block-package”, with the following contents:
   在 “/etc/apt/preferences.d” 文件夹中创建一个文本文件 “block-package”，内容如下：

   Package: ttf-mscorefonts-installer
   Pin: version *
   Pin-Priority: -10
   

3. With a negative priority, the package will not be installed either manually or as a dependency when using apt-get.
   由于设置了负优先级，在使用 apt-get 时，这个软件包无论手动还是依赖都不会被安装。

Reference: http://askubuntu.com/questions/75895/how-to-forbid-a-specific-package-to-be-installed

My Samsung tablet with Android (4.4.2, rooted) has been experiencing random lagging for a while. This affects me most when I’m playing games on it. Earlier today I finally decided to find the root of the problem.

Finding the cause

The ultimate solution is to know which application is causing the lag and disable it. I first went to Settings > General > Developer Options (If you don’t have it, go to Settings > General > About phone/device and tap “Build number” 7+ times to enable it), and ticked “Show CPU usage”. Then you would see an overlay on the top-right corner of your device showing the top (like the Linux command) processes, similar to the image below.

Then I used my device to play games, and wait for the random lagging to happen. When the device start to response slowly, I watched the CPU usage overlay and see “gzip” topping the list. If you are not familiar with Linux, gzip is a compression tool similar to RAR or 7-Zip.

Wrapping (first attempt)

I was expecting some Android application to cause the lagging, instead it’s a command gzip that can be called by anyone. The problem became finding out who called it. Since my device is rooted, I decided to replace the original gzip binary with a wrapper that can log who called it before actually gzipping. Here is the wrapping bash script I used (first version, read on for second version):

#!/system/bin/sh

OPERATION=/system/bin/gzip.real
LOGFILE=/sdcard/gziplog.txt

OPTIONS="$@"

echo "`date` + $EUID `id` + $OPERATION "$@"" >> $LOGFILE

exec $OPERATION "$@"

The script does the following: (1) Log the time, user ID (the $EUID variable turns out to be useless, but `id` worked) and command line parameters to $LOGFILE (a plain text file in the internal storage); then (2) hand over the control to real gzip so that it doesn’t break the gzip functionality.

Then I used Root Explorer to rename /system/bin/gzip to /system/bin/gzip.real, and put my script to /system/bin/gzip (remember to modify the permission to be the same as gzip.real, usually 0755).

After using the device for a while and several lagging happened, I read the logging file and got these lines:

Fri Aug 28 13:53:22 CST 2015 +  uid=2000(shell) gid=2000(shell) groups=1007(log),1009(mount),1015(sdcard_rw),1028(sdcard_r),3003(inet),3006(net_bw_stats) context=u:r:dumpstate:s0 + /system/bin/gzip.real -6
Fri Aug 28 13:54:32 CST 2015 +  uid=2000(shell) gid=2000(shell) groups=1007(log),1009(mount),1015(sdcard_rw),1028(sdcard_r),3003(inet),3006(net_bw_stats) context=u:r:dumpstate:s0 + /system/bin/gzip.real -6
Fri Aug 28 13:55:43 CST 2015 +  uid=2000(shell) gid=2000(shell) groups=1007(log),1009(mount),1015(sdcard_rw),1028(sdcard_r),3003(inet),3006(net_bw_stats) context=u:r:dumpstate:s0 + /system/bin/gzip.real -6
Fri Aug 28 13:56:53 CST 2015 +  uid=2000(shell) gid=2000(shell) groups=1007(log),1009(mount),1015(sdcard_rw),1028(sdcard_r),3003(inet),3006(net_bw_stats) context=u:r:dumpstate:s0 + /system/bin/gzip.real -6

Observe that `id` produced “uid=2000(shell) gid=2000(shell) ...” and the command called is “gzip -6“. This means gzip was called by the shell user, not a specific application, and the data to be compressed was piped in to gzip and then piped out, since there are no input or output file names. (Spoiler: Actually this has shown “context=u:r:dumpstate:s0” which indicated that it was called by “dumpstate“, but I didn’t realize for the first time.)

Wrapping (second attempt)

Then I decided to take the surveillance up a level, and used the following wrapper in place of the first version:

#!/system/bin/sh

OPERATION=/system/bin/gzip.real
LOGFILE=/sdcard/gziplog.txt
TEE="/system/bin/busybox0 tee"
PSTREE="/system/bin/busybox0 pstree"

OPTIONS="$@"

echo "[$$] `date` + $EUID `id` + $OPERATION "$@"" >> $LOGFILE
$PSTREE -p >> $LOGFILE

#exec $OPERATION "$@"
$TEE -a $LOGFILE | $OPERATION "$@"

The difference between it and the previous one is that, it uses Busybox’s “pstree” command to output the process tree of that moment, and “tee” command to record the data piped in and pipe it out again. In order for this to work, I downloaded busybox-armv7l binary (my device has ARMv7 architecture) from the official website and put it to /system/bin/busybox0 with the same permission as gzip.real. You can also use Busybox installer apps and modify the busybox path accordingly.

After a while, I got the following log this time:

[8691] Fri Aug 28 14:30:46 CST 2015 +  uid=2000(shell) gid=2000(shell) groups=1007(log),1009(mount),1015(sdcard_rw),1028(sdcard_r),3003(inet),3006(net_bw_stats) context=u:r:dumpstate:s0 + /system/bin/gzip.real -6
init(1)-+-Binder_2(2299)---{Binder_1}(2360)
        |-DaemonServer(5419)---app_process(8668)
        |-DaemonServer(6687)
<...snip...>
        |-debuggerd(2276)---dumpstate(8690)-+-gzip(8691)---busybox0(8695)
        |                                   `-top(8696)
<...snip...>
========================================================
== dumpstate: 2015-08-28 14:30:46
========================================================

Build: KOT49H.P601ZCUCNH1
Build fingerprint: 'samsung/lt033gzc/lt033g:4.4.2/KOT49H/P601ZCUCNH1:user/release-keys'
Bootloader: P601ZCUCNH1
Radio: unknown
<...snip...>

Observe that [8691] is the gzip wrapper’s PID, and it’s called by “dumpstate“, which is then called by “debuggerd“. The wrapper also logged the data to be compressed, which is 5 MB long and takes 0.14s to be compressed on my PC instead of a poor mobile device.

Final solution

A quick Google told me this is for developers to debug the system state, and since I’m not a developer in this area, I decided to disable it once for all. This is done by using Root Explorer to revoke the execute permissions from the two binaries /system/bin/{debuggerd,dumpstate}.

Now the lagging is gone.