Move service hardening options to override config

Some combination of these options were causing problems with the
functionality of restart.sh as described in the comment and in detail in
issue #7503.

While these seem OK on their face, the implications of this breaking
restart.sh means that they could potentially break other things too.

Thus, we should move these into the optional override file which is in
the administrator's full control, instead of in the default unit, and
leave them off unless a user or package maintainer (e.g. NixOS as
described in the original issue #6952) wants to enable them.

Fixes #7503

debian/conf/jellyfin.service.conf

@@ -3,5 +3,53 @@
 # Use this file to override the user or environment file location.
 
 [Service]
+# Alter the user that Jellyfin runs as
 #User = jellyfin
+
+# Alter where environment variables are sourced from
 #EnvironmentFile = /etc/default/jellyfin
+
+# Service hardening options
+# These were added in PR #6953 to solve issue #6952, but some combination of
+# them causes "restart.sh" functionality to break with the following error:
+#   sudo: effective uid is not 0, is /usr/bin/sudo on a file system with the
+#   'nosuid' option set or an NFS file system without root privileges?
+# See issue #7503 for details on the troubleshooting that went into this.
+# Since these were added for NixOS specifically and are above and beyond
+# what 99% of systemd units do, they have been moved here as optional
+# additional flags to set for maximum system security and can be enabled at
+# the administrator's or package maintainer's discretion.
+# Uncomment these only if you know what you're doing, and doing so may cause
+# bugs with in-server Restart and potentially other functionality as well.
+#NoNewPrivileges=true
+#SystemCallArchitectures=native
+#RestrictAddressFamilies=AF_UNIX AF_INET AF_INET6 AF_NETLINK
+#RestrictNamespaces=false
+#RestrictRealtime=true
+#RestrictSUIDSGID=true
+#ProtectControlGroups=false
+#ProtectHostname=true
+#ProtectKernelLogs=false
+#ProtectKernelModules=false
+#ProtectKernelTunables=false
+#LockPersonality=true
+#PrivateTmp=false
+#PrivateDevices=false
+#PrivateUsers=true
+#RemoveIPC=true
+#SystemCallFilter=~@clock
+#SystemCallFilter=~@aio
+#SystemCallFilter=~@chown
+#SystemCallFilter=~@cpu-emulation
+#SystemCallFilter=~@debug
+#SystemCallFilter=~@keyring
+#SystemCallFilter=~@memlock
+#SystemCallFilter=~@module
+#SystemCallFilter=~@mount
+#SystemCallFilter=~@obsolete
+#SystemCallFilter=~@privileged
+#SystemCallFilter=~@raw-io
+#SystemCallFilter=~@reboot
+#SystemCallFilter=~@setuid
+#SystemCallFilter=~@swap
+#SystemCallErrorNumber=EPERM

debian/jellyfin.service

@@ -13,38 +13,5 @@ Restart = on-failure
 TimeoutSec = 15
 SuccessExitStatus=0 143
 
-NoNewPrivileges=true
-SystemCallArchitectures=native
-RestrictAddressFamilies=AF_UNIX AF_INET AF_INET6 AF_NETLINK
-RestrictNamespaces=false
-RestrictRealtime=true
-RestrictSUIDSGID=true
-ProtectControlGroups=false
-ProtectHostname=true
-ProtectKernelLogs=false
-ProtectKernelModules=false
-ProtectKernelTunables=false
-LockPersonality=true
-PrivateTmp=false
-PrivateDevices=false
-PrivateUsers=true
-RemoveIPC=true
-SystemCallFilter=~@clock
-SystemCallFilter=~@aio
-SystemCallFilter=~@chown
-SystemCallFilter=~@cpu-emulation
-SystemCallFilter=~@debug
-SystemCallFilter=~@keyring
-SystemCallFilter=~@memlock
-SystemCallFilter=~@module
-SystemCallFilter=~@mount
-SystemCallFilter=~@obsolete
-SystemCallFilter=~@privileged
-SystemCallFilter=~@raw-io
-SystemCallFilter=~@reboot
-SystemCallFilter=~@setuid
-SystemCallFilter=~@swap
-SystemCallErrorNumber=EPERM
-
 [Install]
 WantedBy = multi-user.target