redis-server fails to start after 16.04 to 16.10 upgrade

[Andrew France]

After upgrading a 16.04 system to 16.10 with `do-release-upgrade` the `redis-server` package fails to start. I purged and re-installed the package but it made not difference.

I noticed the `journalctl -xe` command contains numerous errors like:
`systemd[14519]: redis-server.service: Failed at step NAMESPACE spawning /usr/bin/redis-server: Too many levels of symbolic links`

But I have been unable to find out what this means. All other programs seem to start on boot normally.

ProblemType: Bug
DistroRelease: Ubuntu 16.10
Package: redis-server 2:3.2.1-1
Uname: Linux 4.8.3-x86_64-linode76 x86_64
ApportVersion: 2.20.3-0ubuntu8
Architecture: amd64
Date: Tue Nov 1 23:06:53 2016
ProcEnviron:
 LANG=en_GB.UTF-8
 PATH=(custom, no user)
 TERM=screen-256color
 SHELL=/bin/bash
SourcePackage: redis
UpgradeStatus: Upgraded to yakkety on 2016-11-01 (0 days ago)

[Andrew France (andrew-avito)]

Changing `ProtectHome=yes` to `no` in `/lib/systemd/system/redis-server.service` allows the service to start. My /home dir is a symlink to a directory on a separate mounted volume, which I assume is the cause of the trouble.

[Andrew France (andrew-avito)]

It's an issue with systemd and symlinks.

[Leonardo Pereira (leonardolamcso)]

This problem did not occur in version 20.04 LTS. But as soon as I upgraded to version 21.04 it started to happen.

[Leonardo Pereira (leonardolamcso)]

Job for redis-server.service failed because the control process exited with error code.
See "systemctl status redis-server.service" and "journalctl -xe" for details.

redis-server.service: Start request repeated too quickly.
redis-server.service: Failed with result 'exit-code'.
Failed to start Advanced key-value store.

[Leonardo Pereira (leonardolamcso)]

I followed that step-by-step and it worked.
https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-redis-on-ubuntu-16-04