Add article about reverting arch packages

content/posts/arch-revert-to-date.md

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+---
+title: Revert Arch linux packages to specific date
+date: 2017-09-11
+image: https://www.lumalab.net/download/archlogo/arch-logo-shiny-dark.png
+subtitle: Arch is well known for going wrong, but today was the first time this affected me doing my job
+---
+
+I'm one of those Arch users that doesn't use arch properly: I install updates daily, including packages from the AUR. This has the great benefit of giving me the most up-to-date packages available from upstream. This has the downside of meaning I have the latest packages from upstream, meaning if something breaks, even temporarily, it breaks for me.
+
+I'm also one of those _crazy_ people who uses arch on my work machine. Craziness aside, it's never caused me an issue, until today.
+
+After running updates this morning, as I normally would, I went to start the project I was working on today locally, and was met with this wonderful message:
+
+```text
+Put stack trace here later!
+```
+
+I knew this was something to do with updates, because that's all that had changed between the last time it worked and now. But I had a feeling rolling back updates to a given date, especially on arch, would be fairly painful. Much to my surprise, it was super simple!
+
+After frantically googling, so my boss didn't notice my downtime, I found [this](https://www.ostechnix.com/downgrade-packages-specific-date-arch-linux/) article, which solved my needs completely. A simple config edit, and 1 command, and I was back to working. 
+
+## Doing the rollback
+The way this solution works is by rather than using the current state of the package repos, we use an archive from a specific date.
+
+### 1. Change mirror to archive
+Edit the mirrorlist to point to the archive at a specific date. Change the contents of `/etc/pacman.d/mirrorlist` to:
+
+```text
+Server=https://archive.archlinux.org/repos/2017/09/08/$repo/os/$arch
+```
+
+Remember to take a backup beforehand just in case! Here's I've set the date to last Friday (8th September 2017), but just replace the date in the URL with the date you need (`YYYY/MM/DD`).
+
+
+### 2. Force install updates
+Force update package repos, and install packages. If there are newer packages installed than are available in the repos, they'll be downgraded.
+
+```bash
+sudo pacman -Syyuu
+```
+
+### 3. Reboot?
+Depending on what packages have been downgraded, you may have to reboot to apply these changes. For the change I needed, a reboot wasn't needed. I just relaunched the terminal, and got on as normal.
+
+## Reverting
+To revert, just restore the backup of the pacman mirrorlist, and re-run the above pacman command.
+
+## Outdated Packages
+Generally, having out of date packages on your system is a bad idea. Not only for security reasons, but stability and compatability. [The article](https://www.ostechnix.com/downgrade-packages-specific-date-arch-linux/) goes through a couple more too.