Tanguy Ortolo

Streamable archive formats

Archive formats such as tar(5) and cpio(5) have the advantage of being streamable, so you can use them for transferring data with pipes and remote shells, without having to store the archive in the middle of the process, for instance:

$ cd public_html/blog
$ rgrep -lF "archive" data/articles \
      | pax -w \
      | ssh newserver "mkdir public_html/blog ;
                       cd public_html/blog ;
                       pax -r"

Read more Using bsdtar to change an archive format

Since systemd is now the default init system under Debian Jessie, it got installed to my system and I had a chance to test it. The result is disappointing: it does not work well with cryptsetup, so I am switching back to SysV init and RC.

Read more Trying systemd [ OK ] Switching back to SysV [ OK ]

Major desktop environments such as Xfce or KDE have a built-in computer suspend feature, but when you use a lighter alternative, things are a bit more complicated, because basically: only root can suspend the computer. There used to be a standard solution to that, using a D-Bus call to a running daemon upowerd. With recent updates, that solution first stopped working for obscure reasons, but it could still be configured back to be usable. With newer updates, it stopped working again, but this time it seems it is gone for good:

$ dbus-send --system --print-reply \
            --dest='org.freedesktop.UPower' \
            /org/freedesktop/UPower org.freedesktop.UPower.Suspend
Error org.freedesktop.DBus.Error.UnknownMethod: Method "Suspend" with
signature "" on interface "org.freedesktop.UPower" doesn't exist

Read more GNU/Linux graphic sessions: suspending your computer

Allowing computer suspend

Major desktop environments such as Xfce or KDE have a built-in computer suspend feature, but when you use a lighter alternative, things are a bit more complicated, because basically: only root can suspend the computer. Possible solutions include:

• using sudo to allow members of a given group to run a suspend command, e.g. pm-suspend as root;
• using a D-Bus UPower thingy, which communicates with a running daemon upowerd:

  $ dbus-send --system --print-reply \
              --dest='org.freedesktop.UPower' \
              /org/freedesktop/UPower org.freedesktop.UPower.Suspend
          

With recent updates of the related Debian packages — no idea of which one exactly — the latter solution may not work any more, in which case it will only return the following error:

Error org.freedesktop.UPower.GeneralError: not authorized

It appears that this error is linked to ConsoleKit, a part of all this modern *Kit gizmo pile. If you are in this case, try prefixing your session launcher with the undocumented dark magic call ck-launch-session. For instance, this is what I have in my .xsession to launch my window manager i3:

exec ck-launch-session i3

Note: I do not know what ck-launch-session does exactly, why it is needed, and I do not want to know. To me, all that WhatsitKit pile is just some opaque, under-documented — as in: no man page — crap, that no one but their author really understand, designed to solve theoretical problems no one really cares about — like: how to allow locally connected users to use the sound card while forbidding it to remote users — while creating new issues such as this one. This stuff is too complex and under-documented for me to dive into it, so if it does not work out of the box, it is just some crap that gets in my way to using my computer as I wish.

Disabling a monitor

In some configurations, you have two monitors and want to disable one. For instance, in addition to my LCD monitor, I have a projector which I only use for movies. According to xorg.conf's man page, it can be disabled this way:

Section "Device"
    Identifier  "Internal graphic card"
    Option      "Monitor-DVI"   "LCD Monitor"
    Option      "Monitor-VGA"   "Projector"
EndSection

Section "Monitor"
    Identifier  "LCD Monitor"
EndSection

Section "Monitor"
    Identifier  "Projector"
    Option      "Enable"    "false"
EndSection

Except that does not work, because contrary to what the man page says the real option to use is not Enable but Disable! So here is the correct configuration to disable that monitor at start-up:

Section "Device"
    Identifier  "Internal graphic card"
    Option      "Monitor-DVI"   "LCD Monitor"
    Option      "Monitor-VGA"   "Projector"
EndSection

Section "Monitor"
    Identifier  "LCD Monitor"
EndSection

Section "Monitor"
    Identifier  "Projector"
    Option      "Disable"   "true"
EndSection

Note: yes, I will send a bug report with a patch against xorg.conf's man page.

Using address extension

Postfix (and many other mail servers) offers one nice address extension feature: addresses like <user+whaterver@> are implicit aliases to <user@>. This allows users to implement a simple measure to fight spam:

1. when SomeCompany® or whatever asks for your email address, give them <user+somecompany@>;
2. if you start receiving spam at that address, you know who sold or was stolen your address;
3. finally, you will be able to disable that address so messages are simply refused with a permanent error code.

Read more Disable your spammed addresses with Postfix