Fedora upgrading
This commit is contained in:
Quentin Dufour
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---
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layout: post
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slug: upgrade-fedora-online
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status: published
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sitemap: true
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title: Upgrade your Fedora online with dnf-system-upgrade
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description: How to efficiently destroy your distribution
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disqus: false
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categories:
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tags:
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- linux
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- fedora
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---
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I have installed Fedora on my computer 3 or 4 years ago. Since this installation, I have installed many packages and upgraded it every 6 months. Unfortunately, Gnome Software has never worked for me, and I never took the time to debug it. Like many people, I am using the old method with `dnf-system-upgrade`, which worked pretty well. But this time, I had a segfault on dnf during the offline upgrade. The only information I got was the following lines:
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```
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kernel: show_signal_msg: 7 callbacks suppressed
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kernel: dnf[846]: segfault at 8 ip 00007f39b860f724 sp 00007ffd00588520 error 4 in libc-2.25.so[7f39b8586000+1cb000]
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kernel: audit: type=1701 audit(1511598827.366:96): auid=4294967295 uid=0 gid=0 ses=4294967295 subj=system_u:system_r:rpm_t:s0 pid=846 comm="dnf" exe="/usr/libexec/s
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systemd-coredump[869]: Failed to connect to coredump service: No such file or directory
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systemd[1]: dnf-system-upgrade.service: Main process exited, code=dumped, status=11/SEGV
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systemd[1]: Failed to start System Upgrade using DNF.
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```
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Just after the segfault, my computer rebooted on Fedora 26.
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## How dnf-system-upgrade works
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*Some information presented here could not be totally accurate. If you have a doubt, please follow the links.*
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`dnf-system-upgrade` use a feature of systemd described here: [Implementing Offline System Updates](https://www.freedesktop.org/software/systemd/man/systemd.offline-updates.html).
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By creating a symlink named `/system-update`, at the next reboot systemd will boot to a specific target named `system-update.target`
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But when will this symlink created ? When you run the following command:
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```
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# dnf system-upgrade reboot
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```
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We can see [in the source of the plugin](https://github.com/rpm-software-management/dnf-plugins-extras/blob/master/plugins/system_upgrade.py) that a symlink pointing to a dnf folder is created:
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```python
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DEFAULT_DATADIR = '/var/lib/dnf/system-upgrade'
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MAGIC_SYMLINK = '/system-update'
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# ...
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os.symlink(DEFAULT_DATADIR, MAGIC_SYMLINK)
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# ...
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reboot()
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```
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We can now investigate which services are triggered by this target:
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```raw
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$ ls /usr/lib/systemd/system/system-update.target.wants/
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dnf-system-upgrade.service fwupd-offline-update.service packagekit-offline-update.service
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```
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We are specifically interested by `dnf-system-upgrade.service` which basically run the following command:
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```raw
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# dnf --releasever=27 system-upgrade upgrade
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```
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At the end of this script, the symlink `/system-update` is destroyed and the computer rebooted.
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## Upgrading online to bypass the bug
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I didn't have any idea to debug this segfault in the offline mode.
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So I searched a way to run this command in an online system.
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If the command segfaults, I'll have some tools to investigate it.
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If the command works, I'll have an upgraded system.
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Before typing any command, you must know that this tool is not intended to be run this way.
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It may break your Fedora installation or kill your family.
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You really should run all your commands in a virtual terminal, as if Gnome crashes during the install, it will not kill dnf.
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First, you must have downloaded the update:
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```
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# dnf upgrade --refresh
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# dnf system-upgrade download --releasever=27
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```
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*For more information, you can refer to the article [Upgrading Fedora 26 to Fedora 27](https://fedoramagazine.org/upgrading-fedora-26-fedora-27/)*
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Then, you will need to update dnf-system-upgrade configuration stored in `/var/lib/dnf/system-upgrade.json` and set "upgrade\_status" to "ready":
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```json
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{
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"download_status": null,
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"upgrade_status": "ready", <--- this line
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"exclude": [],
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"allow_erasing": true,
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"datadir": "/var/lib/dnf/system-upgrade",
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"distro_sync": true,
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"best": false,
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"target_releasever": "27",
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"system_releasever": "26",
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"releasever": "23",
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"install_packages": {},
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"enable_disable_repos": []
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}
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```
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You must create the `/system-update` symlink, otherwise the upgrade command will fail:
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```raw
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# ln -s /var/lib/dnf/system-upgrade /system-update
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```
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And finally, you can run the upgrade command:
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```raw
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# dnf --releasever=27 system-upgrade upgrade
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```
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Your computer will automatically reboot at the end. Now you'll have either a working Fedora 27 or a borken Linux distribution. Good luck and have fun !
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