Migrating between architectures
This page documents two potential methods of migrating installed systems between i686 (32-bit) and x86_64 (64-bit) architectures, in either direction. The methods avoid reinstalling the entire system. One method uses a liveCD, the other modifies the system from within..
- 1 General preparation
- 2 Method 1: Utilising the Arch LiveCD
- 3 Method 2: From a running system
- 4 Cleanup
- 5 Troubleshooting
- 6 See also
Confirm 64-bit architecture
If you are already running x86_64 but want to install i686 this is not relevant and you can skip this step.
In order to run 64-bit software, you must have a 64-bit capable CPU. Most modern CPUs are capable of running 64-bit software. You may check your CPU with the following command:
grep --color '\<lm\>' /proc/cpuinfo
For CPUs that support x86_64, this will return the
lm flag (“long mode”) highlighted. Beware that lahf_lm is a different flag and does not indicate 64-bit capability itself.
You should be prepared for
/var/cache/pacman/pkg to grow approximately twice its current size during the migration. This is assumes only packages that are currently installed are in the cache, as if “pacman -Sc” (clean) was recently run. The disk space increase is due to duplication between the i686 and x86_64 versions of each package.
If you have not enough disk, please use gparted to resize the relevant partition, or mount another partition to /var/cache/pacman.
Please do not remove packages of the old architecture from the cache until the system is fully operating in the new architecture. Removing the packages too early may leave you unable to fall back and revert changes.
The migration may take a substantial amount of time, and it would be inconvenient to interrupt the process. You should plan on at least an hour, depending on the number and size of your installed packages and internet connection speed (although you can download everything before starting the critical part). Please make sure you are connected to a stable power source, preferably with some sort of failover or battery backup.
If the migration fails halfway through, there are packages that can help sort out the situation, but they should be installed before the main packages are migrated. More details about using them under #Troubleshooting below.
One package is, which can be used to revert changes. It is statically linked and does not depend on any libraries. The 32-bit (i686) version should be installed, using
# pacman -S busybox
Another package is Multilib x86_64 repository. It is probably only useful when migrating away from 32 bits; in any case you may safely skip this package. You can use the package to run 32 bit programs by explicitly calling
/lib/ld-linux.so.2. Install with:
# pacman -S lib32-glibc
Method 1: Utilising the Arch LiveCD
- Download, burn and boot the 64-bit Arch ISO LiveCD
- Configure your network on the LiveCD, then pacman to use your new architecture repos
- Mount your existing installation to
/mntdirectory. For example:
mount /dev/sda1 /mnt
- Use the following script to update the local pacman database, get a list of all your installed packages and then reinstall them:
#!/bin/bash MOUNTED_INSTALL='/mnt' TEMP_FILE='/tmp/packages.list' pacman --root $MOUNTED_INSTALL -Sy pacman --root $MOUNTED_INSTALL -Qqet > $TEMP_FILE for PKG in $(cat $TEMP_FILE) ; do pacman --root $MOUNTED_INSTALL -S $PKG --noconfirm done exit 0
Method 2: From a running system
Cache old packages
If you do not have all your installed packages in your cache, download them (for the old architecture) for fallback purposes.
# pacman -Sw $(comm -23 <(pacman -Qq) <(pacman -Qmq))
or use bacman from pacman-contrib package to generate them.
If you are migrating away from 32 bits, now is the time to install 32-bit Busybox:
# pacman -S busybox
Change Pacman architecture
Edit the /etc/pacman.conf file and change Architecture from
auto to the new value. These sed commands may be used:
# sed -i -e s/'Architecture = auto'/'Architecture = x86_64'/g /etc/pacman.conf
and for i686:
# sed -i -e s/'Architecture = auto'/'Architecture = i686'/g /etc/pacman.conf
Pacman’s package repository databases should be manually removed to force synchronisation with the new repositories:
# rm -rf /var/lib/pacman/sync/* # remove existing repository cache # pacman -Sy # sync new architecture repositories
Download new packages
Download the new architecture versions of all our currently installed packages:
# pacman -Sw $(pacman -Qq|sed '/^lib32-/ d') # download new package versions
If there are some packages that cannot be downloaded, please remove them.
If migrating to 32 bits, install the 32-bit Busybox fallback now that Pacman has been configured with the 32-bit architecture:
# pacman -S busybox
Install kernel (64-bit)
Upgrading the kernel to 64 bits (x86_64) is safe and straightforward: 32 bit and 64 bit applications run equally well under a 64-bit kernel. For migration away from 64 bits, leave the 64-bit kernel installed and running for now and skip this step.
To install the standard Arch Linux kernel, use the following command:
# pacman -S linux
Now is the time to install the lib32-glibc fallback:
# pacman -S lib32-glibc
Reboot and verify it is running the x86_64 architecture:
$ uname -m
This is the time to switch to a text-mode virtual console (e.g. Ctrl+Alt+F1) for the rest of the process. You should be fine using a pseudo-terminal like SSH but it is not advised. There will be several packages removed and replaced during the update process that may cause X11 desktops to become unstable leaving your system in an unbootable state.
Using pactree to get a deep dependency list for pacman:
# pactree -l pacman | pacman -S -
Immediately following this command only Busybox, Bash and Pacman will be executable until the other packages are migrated below. You must not reboot your system until the following commands have been completed. You have been warned.
Install remaining packages
Install all of the previously downloaded replacements for the new architecture. (Go get a drink and make a sandwich; this could take a while.)
# pacman -S $(pacman -Qq)
For migration away from 64 bits, you may want to skip installing a 32-bit kernel in the command above, since the old 64-bit kernel will still run 32-bit programs.
After this step the migration in either direction should be complete and it should be safe to reboot the computer.
You are now free to remove Busybox and lib32-glibc.
# pacman -Rcn busybox lib32-glibc
Makepkg compiler flags
During the upgrade the new version of
/etc/makepkg.conf may be stored as
/etc/makepkg.conf.pacnew. You will have to replace the old version or modify it, if you want to compile anything with makepkg in the future.
# mv /etc/makepkg.conf /etc/makepkg.conf.backup && mv /etc/makepkg.conf.pacnew /etc/makepkg.conf
It might also be a good idea to just get a list of "new" additions to
/etc. You can get a list with the following command:
# find /etc/ -type f -name \*.pac\*
During the upgrade, when glibc is replaced by the new architecture version, old architecture versions of many programs will not run. If problems occur, you can solve them withand .
In Arch, Busybox is statically linked; it can run without any libraries. There are many commands available to you. For example, to extract an i686 version of Pacman from a cached package:
# busybox tar xf /var/cache/pacman/pkg/pacman-3.3.2-1-i686.pkg.tar.gz -C <some folder>
Example run 32 bit
# /lib/ld-linux.so.2 /bin/ls