This is a guide to replace a running Linux system on a remote server. While Arch makes a good server system, it is not usually the pre-installed distribution of choice.
- 1 Introduction
- 2 Backup and Preparation
- 3 Prepare the intermediate system
- 4 Create a new swap file
Many providers offer systems called rescue systems or remote consoles, which is often just a bootdisc stored on a network card. This boots into a rudimentary system which just exists in your RAM. Thus you will have the ability to partition your harddrive as you like.
This document outlines the solution for servers without a rescue systems but have a swap partition. You can disable the swap partition and set up your intermediate system there. When you finish this tutorial you will have a base Arch Linux, which can be accessed via SSH.
Backup and Preparation
During the procedure you WILL ERASE ALL DATA on your former server. Backup all your data including mails, webservers, etc. Have all information at your fingertips. Preserve all your server configurations, hostnames, etc.
Here is a list of data you will likely need:
- IP address
- hostname(s), (note: rootserver are mostly also part of the providers domain, check or save your
/etc/hostsbefore you delete)
- DNS server (check
- SSH keys (if other people work on your server, they will have to accept new keys otherwise. This includes keys from your Apache, your mail servers, your SSH server and others.)
- Hardware info (network card, etc. Refer to your pre-installed
- Grub configuration files.
In general, it is a good idea to have a local copy of your original
/etc directory on your local hard drive.
Prepare the intermediate system
The intermediate system is the system which is used as a place where you setup your new disc layout and install the final system. There is no need to install more then the absolutely necessary packages in it. In addition to the base system you will need wget to fetch some software and an ssl server.
Create a new swap file
If you're paranoid or have very little RAM available you might want to add a swap file as swapspace before you disable the swap partition. Note that you do not need running daemons such as mailserver, http-server etc. When you stop them you can free memory at the remote machine.
The following commands create a file filed with zeros, formats it as swap space, activates the swap file, forces writing of the buffer cache to the disk, and then checks for active swap files.
# dd if=/dev/zero of=/swapfile bs=1024 count=512288 # mkswap /swapfile # swapon /swapfile # sync # cat /proc/swaps
Set old swap partition as new root partition
/etc/fstab to find your swap partition. Assuming your hard drive is located on sdaX (X will be a number).
Do the following:
Disable the swap space:
# swapoff /dev/sdaX
Create a filesystem on it
# fdisk /dev/sda (set /dev/sdaX ID field to "Linux" - Hex 83) # mke2fs -j /dev/sdaX
Create a directory to mount it in
# mkdir /mnt/newsys
Finally mounts the new directory for installing the intermediate system.
# mount -t ext4 /dev/sdaX /mnt/newsys
Install the intermediate system
Setup the intermedia system environment for pacman following a method in Install from Existing Linux.
Things to check before you boot
You will have to chroot into your new system to bring up a kernel. When you're in it you will have to setup a root password, otherwise SSH will not let you into your system. Also your bootloader must be directed to your new system. You might want to configure your bootloader to be able to boot into your old system. This makes it easier to use the recovery console in case you have one.
mount essential systems
# mount -o bind /dev /mnt/newsys/dev # mount -t proc none /mnt/newsys/proc
Chroot into your new system:
# chroot /mnt/newsys /bin/bash
Make sure you have a network and check by this method.
Now you should have pacman available to manage your system. You will need a kernel and an ssh server to reboot into your rescue system. Once you are installing stuff also consider the editor of your choice (nano, joe) if you dislike vi.
# pacman -S linux openssh
Set up a bootloader following guide in Installation Guide. Set up your bootmanager to the new system
Before proceeding double check that you:
# start sshd # set a root password
All this is necessary to get a working system. Enter
Prepare a home for your new production server
Give the server time to reboot and then ping it to ensure you can access it.
SSH into your new Arch system. If you forgot to copy your ssh-keys the output will tell you why. Follow the lines to get rid of it. Make sure you understand where you are - at your former swap partition. In your private little rescue system. You are surrounded by your old system partition. If you are freaky enough to choose option #1 you are on your own for this part. To use parted is not the world's hardest challenge at all.
- You want to migrate your old data to the new system. You use
partedto create a rescue partition and copy all your data to it.
- You already have a backup somewhere on the net (good boy!) then you can call cfdisk without a risk and set up your new disc layout directly.
- You want to migrate your old data to the new system. You use
Let's consider a good layout first: You are here in a rescue system. Useful, isn't it? Let's have rescue system at your harddrive if your server got hacked or if you have to work at the actual system. This can also be useful if you set up your server and need to interrupt your work. What to do, leave your server there without a firewall and no root passwords set for the MySQL-server? Bad idea! Boot into your rescue system just waiting to ssh into it again and continue your work. You can also add all the tools you need to work to this system and you're not restricted to the minimal system from the providers rescue console(if you have one). Now swap partitions, where you are currently, are mostly at the very beginning of a disc layout. Don't waste fast parts of the hd for your rescue system! Place the rescue system at the end (maybe 512-1024MB) of your disc layout.
Now the idea for the complete layout (It'll depend a bit on the former layout and where the partition you are currently working on is located). Some people might want to use Confixx or Vistas to maintain their domains and e-mail accounts. This will require a different layout but is not covered by this tutorial at all. We will suggest this layout:
- part1 swap 512MB
- part2 / 2048MB
- part3 /home depends on size of the disc
- part4 -- extended --
- part5 /backup usually the same size as /home
- part6 / for rescue system 1024MB
Now make your layout. When you do so do not forget that you will have to leave the partition you are currently working on intact!!!
# parted /dev/discs/disc0/disc
# cfdisk /dev/discs/disc0/disc
Create filesystems as desired and mount your new root partition to
# mkdir /mnt/newsys # mount -t ext3 /dev/discs/disc0/part3 /mnt/newsys
Set up your new system
We need archbootstrap again and this uses, so make sure you install it.
Copy archbootstrap from your old home, which you will have to mount, or copy it again via scp. Alternatively you can extract the original Arch setup script from the cd or from the floppy images. I assume you used archbootstrap again and have the base installed to
/mnt/newsys. You can edit your
/etc stuff manually again, or you can copy:
# cat /etc/fstab > /mnt/newsys/etc/fstab # cat /etc/pacman.conf > /mnt/etc/pacman.conf # cat /etc/hosts > /mnt/etc/hosts # cat /etc/hosts.allow > /mnt/etc/hosts.allow # cat /etc/rc.conf > /mnt/etc/rc.conf # cat /etc/modprobe.d/modprobe.conf > /mnt/etc/modprobe.d/modprobe.conf # cat /etc/resolv.conf > /mnt/etc/resolv.conf
When you're done set up your final
/mnt/newsys/etc/fstab (Edit to suit your system):
# # /etc/fstab: static file system information # # <file system> <dir> <type> <options> <dump> <pass> none /proc proc defaults 0 0 none /dev/pts devpts defaults 0 0 none /dev/shm tmpfs defaults 0 0 tmpfs /tmp tmpfs defaults 0 0 #sysfs /sys sysfs defaults 0 0 usbdevfs /proc/bus/usb usbdevfs defaults 0 0 /dev/cdroms/cdrom0 /mnt/cd iso9660 ro,user,noauto,unhide 0 0 /dev/cdroms/cdrom0 /mnt/dvd udf ro,user,noauto,unhide 0 0 /dev/floppy/0 /mnt/fl vfat user,noauto,unhide 0 0 # the production system /dev/discs/disc0/part1 swap swap defaults 0 0 /dev/discs/disc0/part2 / ext3 defaults 0 1 /dev/discs/disc0/part3 /home ext3 defaults 0 1 # the backup system /dev/discs/disc0/part5 /mnt/backup ext3 defaults,noauto 0 1 # the rescue system if necessary /dev/discs/disc0/part6 /mnt/rescue ext3 defaults,noauto 0 1
Don't forget to make a directory for the backup
# mkdir /mnt/backup
Again, do not forget to copy your ssl keys. Mount devfs and proc:
# mount -t devfs none /mnt/newsys/dev # mount -t proc none /mnt/newsys/proc
Chroot into your soon to be production system, set a root password, and install essential software
# chroot /mnt/newsys /bin/bash # passwd # pacman -S linux openssh mc wget nano
/mnt/newsys/boot/grub/menu.lst to default it to your new production system.
# install-grub /dev/discs/disc0/disc dev/discs/disc0/part2
Double check that you have performed all necessary steps (as for setting up the rescue system), exit chroot, and reboot.
Now you have Arch Linux running at your server. More things need to be done to turn it into something useful.