Category Archives: UNIX variants

UNIX variants (or formally POSIX-compliant systems), a family of operating systems.

Enable Natural Scrolling for Trackpads Using libinput

Libinput is a library to handle input devices in Wayland and X.Org. It can be used as a drop-in replacement for evdev and synaptics in X.Org, and it is supported by a wide range of desktop environments, including GNOME and Xfce. In this post, we will see how to enable natural scrolling for trackpads using libinput. We will also leave mouses alone, i.e., no natural scrolling for mouses.

First, we need to know the name of the trackpad to enable natural scrolling for. This can be easily known by executing xinput --list. My output includes the following:

⎡ Virtual core pointer                          id=2    [master pointer  (3)]
⎜   ↳ Virtual core XTEST pointer                id=4    [slave  pointer  (2)]
⎜   ↳ bcm5974                                   id=13   [slave  pointer  (2)]

It is easy to see that my trackpad is bcm5974.

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Parallelize make by Default

The make utility is an standard utility on POSIX systems (GNU/Linux, macOS, etc.) that update files derived from other files, such as compiling source files to their binary forms. It is widely supported and used across different fields such as organizing and building C/C++/Fortran projects, building Sphinx documentation, etc.

The most popular implementation of the make utility is probably GNU make, which is usually the default make program on various GNU/Linux distributions. (On macOS, the version of the default GNU make is pretty old. Please consult Install and Use GNU Command Line Tools on macOS/OS X for a newer version.) It adds one very important feature besides the standard make specification: parallelization. The command line option -j can be used to specify the maximum number of jobs that it is allowed to run simultaneously. However, it is quite annoying to type up this option every time when using it—we want a setting such that the CPU can be fully utilized by default. To achieve this goal, add the following lines to your ~/.bashrc if you use bash or ~/.zshrc if you use zsh:

if type nproc &>/dev/null; then   # GNU/Linux
  export MAKEFLAGS="$MAKEFLAGS -j$(($(nproc)-1))"
elif type sysctl -n hw.ncpu &>/dev/null; then   # macOS, FreeBSD
  export MAKEFLAGS="$MAKEFLAGS -j$(($(sysctl -n hw.ncpu)-1))"

The code above sets the envrionmental variable MAKEFLAGS, which specifies the command line arguments of any invoked make subprocesses. It is set such that the maximum number of jobs that is allowed to be run simultaneously is equal to the number of available CPU cores minus 1. In this way, the hardware is more or less fully utilized when using make, with one CPU core left for other potential tasks on the system.

Attachment Reminder in Emacs message-mode

When sending out an email, sometimes we just forgot to attach the attachments. An attachment reminder can largely prevent this: You are asked to confirm whether you have forgotten the attachments if your message body shows that you may need one. However, Emacs by default does not provide such a feature in its mail composing mode message-mode, which is used in email clients such as gnus and mu4e. Here is an attachment reminder based on this comment:

(defun my-message-current-line-cited-p ()
  "Indicate whether the line at point is a cited line."
    (string-match (concat "^" message-cite-prefix-regexp)
                  (buffer-substring (line-beginning-position) (line-end-position)))))

(defun my-message-says-attachment-p ()
  "Return t if the message suggests there can be an attachment."
    (goto-char (point-min))
      (let (search-result)
            (and (setq search-result (re-search-forward "\\(attach\\|pdf\\|file\\)" nil t))

(defun my-message-has-attachment-p ()
  "Return t if the message has an attachment."
    (goto-char (point-min))
      (re-search-forward "<#part" nil t))))

(defun my-message-pre-send-check-attachment ()
  (when (and (my-message-says-attachment-p)
             (not (my-message-has-attachment-p)))
        (y-or-n-p "The message suggests that you may want to attach something, but no attachment is found. Send anyway?")
      (error "It seems that an attachment is needed, but none was found. Aborting sending."))))
(add-hook 'message-send-hook 'my-message-pre-send-check-attachment)

If “attach”, “pdf” or “file” are in the message you are sending, a confirmation would be required to confirm the attachments if they are not attached.

Set up Synapse (Matrix Homeserver) on Ubuntu 16.04

Matrix is an open standard for decentralized persistent communication, shares somewhat similar goals to Jabber/XMPP. It attracts people from using centralized communicating software such as Facebook Messenger, WhatsApp, etc. In the Matrix protocol, a piece of software called “homeserver” plays a key role to connect users. To use Matrix, one such server must be set up. In this post, we will set up Synapse, an implementation of the Matrix homeserver maintained by the Matrix team, using a minimal configuration on Ubuntu 16.04.

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A Better ls Command

The ls command is a command to list files on a UNIX-like system. It is probably one of the most used command. However, a plain ls command without any polishing may look really “plain”. Here, we will slightly configure this command to make it more usable:

  • More colorful output
  • Automatic pagination for long file lists
  • File type indication
  • Human readable sizes
  • Natural ordering of files


Output of ls before configuration

Output of ls before configuration

Output of ls after configuration

Output of ls after configuration

ls pagination

Pagination for ls

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Prevent Browser Processes Started by Emacs from Being Killed When Emacs Exits on GNU/Linux

The function browse-url in Emacs can be used to start a browser process to visit a given URL. It is used by many packages such as org-mode, mu4e, etc. However, on GNU/Linux, by default a new browser process started by browse-url will be killed if the Emacs process exits. To prevent the browser process from being killed, add the following code to your Emacs init file:

(when (and (executable-find "setsid") (executable-find "gnome-open"))
  (setq browse-url-browser-function
        (lambda (url &optional ignored)
          (start-process "" nil "setsid" "gnome-open" url))))

You will need both the setsid and gnome-open commands available. Note that replacing gnome-open with xdg-open is not guaranteed to work.

Installing Emacs from Source: Avoid the Conflict of ctags

If installing Emacs from source, an executable named ctags will be installed by default. However, many systems such as GNU/Linux, FreeBSD and macOS often already have an executable named ctags installed, such as Exuberant Ctags or Universal Ctags, which then causes conflict. To avoid this conflict, we can use the switch --program-transform-name='s/^ctags$/ctags.emacs/' when running configure to rename ctags to ctags.emacs. For example:

cd /path/to/emacs-source
mkdir build && cd build
../configure --program-transform-name='s/^ctags$/ctags.emacs/'

After that, running make install will install the Emacs ctags executable as ctags.emacs.

Speed Test: Check the Existence of a Command in Bash and Zsh

In both bash and zsh, there are multiple methods to check whether a command exists. In this post, a set of speed tests will be performed on them to find the fastest way in each of the two shells (NOT to compare the two shells). We will test 5 different methods (foobar is the command to test for existence in the list):

  • type foobar &> /dev/null
  • hash foobar &> /dev/null
  • command -v foobar &> /dev/null
  • which foobar &> /dev/null
  • (( $+commands[foobar] )) (zsh only)

All the methods listed above will have a return status of zero if the command foobar exists, otherwise non-zero. That is, after replacing testing-command by any of the commands listed above, you can test the existence of the command foobar by executing testing-command && echo exist || echo non-exist.

Throughout this post, ls will be the command that is used for testing existence, which does exist on the system which runs the tests. The test environment is Debian Jessie with bash 4.3.30 and zsh 5.0.7 on Intel Xeon processor E3-1240 v3 (8 MB Cache, 3.4 GHz). The test scripts are also available at the end of the post.

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Restore the Previously Canceled Command in Zsh

In zsh, it is often annoying that we can’t easily restore the command we just canceled by CtrlC: canceled commands are not recorded into the history file and thus cannot be restored by searching previous commands. To make the restoration possible, zsh provides a variable ZLE_LINE_ABORTED which keeps a record of the last command that was canceled—everything looks so simple. However, for some reasons, such as canceling stuck tab completion, we often push CtrlC for more than once—but ZLE_LINE_ABORTED would become empty if CtrlC is used on an empty line! Thanks to the great extensibility of zsh, we can solve this issue by tweaking zle-line-init (add the following to your ~/.zshrc):

function zle-line-init {
  # Your other zle-line-init configuration ...

  # Store the last non-empty aborted line in MY_LINE_ABORTED
  if [[ -n $ZLE_LINE_ABORTED ]]; then

  # Restore aborted line on the first undo.
  if [[ -n $MY_LINE_ABORTED ]]; then
    local savebuf="$BUFFER" savecur="$CURSOR"
    zle split-undo
    BUFFER="$savebuf" CURSOR="$savecur"
zle -N zle-line-init
  • Line 1: Define the zle-line-init widget which will be executed every time when the a new command line is ready to take input.
  • Line 5-7: If ZLE_LINE_ABORTED is non-empty, save it to MY_LINE_ABORTED.
  • Line 10-16: If MY_LINE_ABORTED is non-empty, the initial undo will restore the contents in MY_LINE_ABORTED. Also see man zshzle for an explanation of split-undo.
  • Line 18: Install the widget zle-line-init.

Now type any command and push CtrlC twice and undo (bound to Ctrl/ by default): your canceled command is back!

Note that if you use zsh-autosuggestions this code snippet somehow breaks it. Adding _zsh_autosuggest_widget_clear before the end of zle-line-init would fix it.