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marcan / takeover.sh

Wipe and reinstall a running Linux system via SSH, without rebooting. You know you want to.
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switching TTY fails and blocks Debian OS replacement #9

Closed moralrebuild closed 4 years ago

moralrebuild commented 5 years ago

I'm trying to evaluate if it can be used for my Xen based VPS since the vendor provides neither custom ISO nor rescue image interfaces. But the VPS has only 1GB RAM and the recommended System Rescue CD takes more than 2.7GB after unsquashfs.

marcan commented 5 years ago

You can use a smaller system or roll your own (e.g. debootstrap something). Just find some similar rescue live environments you may want to try, unpackage them, and chroot in and see if they work well.

moralrebuild commented 4 years ago

Thanks for your instructions. I have installed minibase of Debian 10 (buster) as the rescue OS. But I failed to run the scripts under my existing Debian 9 (stretch, virtualbox guest as experiment):

root@stretch:/# sh /takeover/takeover.sh
Please set a root password for sshd
New password:
Retype new password:
passwd: password updated successfully
Setting up target filesystem...
Mounting pseudo-filesystems...
Checking and switching TTY...
/takeover/takeover.sh: 40: /takeover/takeover.sh: cannot open /takeover//dev/pts/1: No such file

Could you please have a look? Thanks.

mikeymop commented 4 years ago

PTS/1? Try it over ssh. See if it works?

On Fri, Jul 12, 2019, 1:11 PM Capmus Banon notifications@github.com wrote:

Thanks for your instructions. But I failed to run the scripts under my Debian 9 (stretch):

root@stretch:/# sh /takeover/takeover.sh Please set a root password for sshd New password: Retype new password: passwd: password updated successfully Setting up target filesystem... Mounting pseudo-filesystems... Checking and switching TTY... /takeover/takeover.sh: 40: /takeover/takeover.sh: cannot open /takeover//dev/pts/1: No such file

Could you please have a look? Thanks.

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moralrebuild commented 4 years ago

In fact, it indeed ran over ssh session:

root@stretch:/# tty
/dev/pts/1
root@stretch:/# uname -a
Linux stretch 4.9.0-9-amd64 #1 SMP Debian 4.9.168-1+deb9u3 (2019-06-16) x86_64 GNU/Linux
root@stretch:/# cat /etc/debian_version
9.9

It looks got broken at this line:

exec <"${TO}/${TTY}" >"${TO}/${TTY}" 2>"${TO}/${TTY}"

To be honest, I don't fully understand this command but often use below one in my own scripts:

exec command <> /dev/pts/1 2>&1
moralrebuild commented 4 years ago

This is the fix I used to make it work for modern Debian/ArchLinux:

sed -i 's|^./busybox mount -t devpts devpts dev/pts|./busybox mount --bind /dev/pts dev/pts|'  ${TO}/takeover.sh
moralrebuild commented 4 years ago

Additionally, need to manually create a directory for ssh daemon. Otherwise you get failure by "Missing privilege separation directory: /run/sshd"