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Hello everyone, welcome to my presentation.

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I will introduce GNU/Screen to Debian Installer today.

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I will show you its background.

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What is Debian Installer,

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What is GNU/Screen,

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Why I want GNU/Screen in Debian Installer

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and How to add GNU/Screen support in it.

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First, The background.

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I know that most of you know the Debian Installer.

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It is just an installer.

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But actually, It is a bootable Debian environment,

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which is minimized in size.

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That is to say, there is no document in the image.

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There is no other non-replicated usually-useful information for normal people, which is usually putted in "/usr/share/doc".

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But installer stage, we don't need them.

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So, It contributes for minimizing environment.

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Previously, we have a installer in one or two floppy disks.

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It means that installer was very small.

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Nowadays, it is not possible.

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Because the kernel size is already over size of the floppy.

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Second, there is a partitioner inside the installer.

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So, you can do the partition and create a new disk image inside the installer.

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After that, we can do the "debootstrap" to install Debian environment for you.

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Finaly, the installer will install boot loader.

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There is all kinds of boot loader, such as <b>GRUB</b> for <i>PC</i> or for <i>ARM64</i>.

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For <i>ARM</i> platform, such as <i>armel</i> or <i>armhf</i>, we use <b>flash-kernel</b> as a boot loader.

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What is GNU/Screen?

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First, It is a terminal multiplexer.

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It means that you can have multiple virtual terminal in real terminal.

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And you can switch one virtual terminal to another virtual terminal by a shortcut.

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In GNU/Screen, short key is "Ctrl-A + 1", 2, 3, 4...

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And Tmux (GNU/Screen alternatives)[br]use "Ctrl-B + 1" 2, 3, 4.

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Then you must be thinking why we need GNU/Screen in Debian Installer.

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What is the benefit?

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Let me show you normal installer.

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This is a normal installer.

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We have UI.

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And if we face some problem, such as partitioning or creating new disk image, we want to check the log.

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We can press the key "Alt-F4"[br]to switch to the log console.

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This is a case for normal PC.

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If you want to switch back,[br]we can press the "Alt-F1".

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I can show you the demo.

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This is a normal Debian Installer screen.

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I can enter "Alt-F2".

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Command line appears.

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I can see lots of stuff here.

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By "Alt-F4", you can see the logs here.

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If we want to turn back,[br]we can enter "Alt-F1".

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Then we go back.

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This is a case for normal PC.

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But, there is no such convenient methods[br]in embedded.

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For embedded device[br]such as <i>armel</i> or <i>armhf</i>

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we usually install using the serial console[br]or the SSH over the network.

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So, there is the only one real screen[br]for you.

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There is no other screen.

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Actually, there is a way.

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You can see the previous page.

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There is a "Go Back" option here.

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We can go back and we can have this menu.

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This is an advanced menu and you can enter a shell from here for embedded device.

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After you enter a shell,[br]you can check the logs.

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The log is in "/var/log/syslog".

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It is there, you can check it.

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But, if you want to do it,

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every time you have to go back[br]and enter the shell.

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You cannot do it all the time either

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Because sometimes the installer is running to install packages.

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You cannot do it at anytime[br]like in a normal PC.

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I was just thinking,

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if we have GNU/Screen introduced[br]into the Debian Installer,

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we can have it simple and convenient as a normal PC in the embedded area like <i>armel</i>.

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So, I have started to work for it.

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So, How to achieve it?

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After some search, I found that

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I need to support GNU/Screen binary package and its dependencies such as library to support udeb.

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udeb is special format for Debian Installer[br]which minimize installer image.

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That is to say,[br]it remove documents for example.

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So, we have to support udeb[br]for GNU/Screen and its library.

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And, we need to add those udebs[br]into the Debian Installer image.

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The third one is that we need to write some script to start GNU/Screen in Debian Installer.

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First, udeb support.

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Normally, udeb is controlled by "debian/control".

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it is like every binary packages[br]for the source packages.

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So we just add additional section[br]for supporting a udeb (new binary).

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After that, we just create a new "-udeb.install" file.

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And it is almost identical to the original ".install" file, but entries for unnecessary file are removed.

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After that we can create a patch.

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Then submit it to package maintainer[br]to let him or her to incorporate my changes.

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We add the new udeb package.

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But, if the package is maintained by DM,

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unfortunately DM need to ask DD[br]to sponsor the package to upload.

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For the same reason, the package will stay[br]in NEW queue in ftp-master.

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And we need to wait the ftp-master[br]to approve the upload.

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So, it takes much longer time[br]than common packages.

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What I do is to add these udeb support[br]of GNU/Screen and it's dependencies.

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I created four Bug reports,[br]actually it is four bugs with patches

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After that, we can have udeb package[br]that are ready to use.

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But, we still need to include[br]in the Debian Installer image.

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So, I patched to "debian-installer.git" repository[br]to supporting it.

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And finally we need to start GNU/Screen command[br]after we started Debian Installer.

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We also need GNU/Screen configuration to emulate Debian Installer environment like PC.

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We actually have four virtual screen[br]in the Debian Installer.

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First one is main screen, second is command[br]line console, and last is log console.

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We want to emulate them.

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I want to show you the demo.

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Actually, I run the Debian Installer[br]on virtual machine.

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This is the Debian Installer[br]with GNU/Screen support.

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So, we have four virtual terminals here,[br]1, 2, 3, 4.

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And I can switch terminal by ashortcut[br]such as "Ctrl-A 2", "Ctrl-A 3", and "Ctrl-A 4".

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It is a log.

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As a PC side, as you see now,[br]it seems not much useful.

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Because we can use "Alt-F1", "Alt-F2"[br]and "Alt-F3" to switch.

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But for embedded side, It is much useful.

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I have a progress update.

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Actually these action items[br]are already done.

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For example, first two packages are for library.

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Actually, it was not needed at all.

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Because, I learned that from Mr. Laurent,

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GNU/Screen can be configured[br]to compile twice.

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First time is for normal GNU/Screen and second time is for the one which does not use <i>audit</i> and <i>pam</i> library.

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so it can make GNU/Screen udeb binary minimized.

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Actually, library which needs[br]to be really supported is <i>ncurses</i>.

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<i>ncurses</i> has been uploaded to the ftp-master two weeks ago with the GNU/Screen binary package.

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For Debian Installer image, I just pushed a commit after Debian Installer Stretch Alpha 7 was released this week.

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Since I just pushed the commit[br]after the release,

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you can now try GNU/Screen[br]in Debian Installer daily image.

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Which device will benefit from it?

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These are usual some ARM boards installed[br]by serial console or SSH network console

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and some big machines[br]like SPARC64 or IBM s390/s390x.

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Even some PC can benefit from it.

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Because some PC are headless.

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There is no HDMI or VGA ports[br]on that kinds of PC-server-like PC.

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I would like to thank various people through early request-for-comment stage on my proposal.

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And, the help during[br]my udeb package upload stage.

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Thank you very much.

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[Applause]

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Are there any questions?

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[chair]: OK, do it.

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[questioner 00]: First of all, I use a SPARC embedded systems all the time.

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[questioner 00]: So, absolutely this will be a great help.

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[questioner 00]: Thank you very much for all your work.

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[questioner 00]: I really appreciate this.

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[question 00-00]: What was the one[br]thing that you found hardest with doing this?

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[question 00-01]: What did make you surprised the most "How easy it was"?

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Actually, most difficult part[br]is uploading the package.

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Because one package is maintained by DM.

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Usually DM can upload[br]without DD sponsorship.

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But, since udeb is regarded as new package,

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we need a DD to sponsor it.

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I think it takes almost two month through the process.

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[questioner 00]: And one thing you found very easy to do,

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[questioner 00]: which you thought got to be hard?

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mmm...

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[questioner 00]: Nothing is not all hard?

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[laughs]

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From technical side, it was not hard.

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Because everything is there.

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I just write some simple patch[br]to add udeb support

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and some script to start[br]GNU/Screen in Debian Installer.

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So, from technical side, it is not so difficult.

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[questioner 00]: Awesome.

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Thank you.

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[questioner 00]: Next question?

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[questioner 01]: You said that it was already in Stretch Alpha 7...

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No, I pushed my commit after Stretch Alpha 7.

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[questioner 01]: OK, So is it gonna be after the freeze?

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Yes.

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[questioner 01]: OK.

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[question 01-00]: Do you know if adding all these components related to GNU/Screen, how much the size of image will be increased in?

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[questioner 01]: A lot or not much? Does it make any difference?

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Yes, Debian Installer image size will be little bit larger than before.

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For example, there are "QNAP" series which is armel architecture machine.

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"QNAP" series are supported by Debian Installer.

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But, "QNAP" series has size limitation.

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Because we put the kernel and initrd image[br]in flash memory

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and the flash memory size is about 2 MB for kernel and 4 MB for initrd.

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So, the size is limited.

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Whereas, the size of GNU/Screen udeb[br]package is about 500 KB.

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So, it might be impossible incorporate with this new feature into that specific images.

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For other images, I think it is OK.

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There is no big size limitation concerned.

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Currently, it is in Debian Installer daily build image.

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So, you can just try it in daily build image.

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And, URL is "https://d-i.debian.org/daily-images/".

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There are many images in there.

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Because there are images for all suppored architectures such as amd64 and GNU Hurd etc.

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So, you need to choose the right architecture and image.

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This is my talk. Thank you very much.

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[Applause]