C8

docs/distributions/c8.md

+# CentOS 8
+
+## Practical info
+
+!!! danger ""
+    Upstream support : until 2029-5-31
+
+## Upstream updates
+
+Upstream updates are handled by a [Nomad job](https://gitlab.cern.ch/linuxsupport/cronjobs/centos8_snapshots/).
+
+The job runs automatically every day at 8am. It creates daily snapshot directories
+in `/mnt/data1/dist/cern/centos/8-snapshots/` and maintains the symlinks from `8`,
+`8-testing`, etc. to the appropriate daily snapshot. The `-testing` symlinks
+point to that day's snapshot (see note), and the production (ie. non -testing)
+ones point to last Tuesday's snapshot. Production symlinks are changed on Wednesdays
+("last Tuesday" on a Tuesday is a week ago).
+
+!!! note ""
+    Symlinks are not modified on weekends or between December 16th and January 6th.
+    Snapshots will still be created, though.
+
+
+### Stopping modifications to symlinks
+
+Changes to symlinks can be manually stopped by creating `.freeze.*` files in
+`/mnt/data1/dist/cern/centos/`. You can create the file `.freeze.8all` to stop
+updating all symlinks, or create specific ones for each symlink (ie. `.freeze.8`,
+`.freeze.8.0.1905-testing`, etc.).
+
+Changes to symlinks may also be automatically stopped if the job detects changes
+to ["dangerous" RPMs](https://gitlab.cern.ch/linuxsupport/cronjobs/centos8_snapshots/blob/master/centos8_snapshots/common.sh#L20).
+When that happens, an email will be sent to lxsoft-admin and the `.freeze.8all`
+file will be created automatically. You will have to take manual action to ensure
+the update will work as expected and then remove the `.freeze.8all` file to allow
+symlink updates to proceed.
+
+### Manually updating symlinks
+
+You can also manually point symlinks to a more up-to-date snapshot. The symlink
+will not be moved backwards in time, but it will move forward again as necessary.
+
+For instance, on Wednesday the 2nd, the production symlinks would point to Tuesday
+the 1st. On Thursday an emergency security patch is released and you manually
+modify the production symlinks to point to Thursday's snapshot. The links will
+continue pointing to that day until Wednesday the 9th, when they will be
+automatically updated to point to Tuesday the 8th.
+
+The recommended method of updating the links is as follows:
+
+```bash
+# cd /mnt/data1/dist/cern/centos
+# ln -vfsT 8-snapshots/20191005 8.0.1905
+```
+