Provide log file for krb5kdc by default

[Karl-Philipp Richter]

It'd be nice if `kdc5krb` would log to a file in an intuitive location like `/var/log/kerberos/kdc.log`. Since the service runs as `root` it's only necessary to add `/var/log/kerberos` to `ReadWriteDirectories` in the `systemd` unit.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: krb5-kdc 1.13.2+dfsg-5 [modified: lib/systemd/system/krb5-kdc.service]
ProcVersionSignature: Ubuntu 4.4.0-22.39-generic 4.4.8
Uname: Linux 4.4.0-22-generic x86_64
NonfreeKernelModules: openafs
ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
Date: Fri May 13 17:43:48 2016
InstallationDate: Installed on 2015-04-20 (389 days ago)
InstallationMedia: Ubuntu-Server 14.10 "Utopic Unicorn" - Release amd64 (20141022.2)
ProcEnviron:
 TERM=screen.xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: krb5
UpgradeStatus: Upgraded to xenial on 2016-03-03 (70 days ago)

[Sam Hartman (hartmans)]

I think it logs to syslog.
Are you seeing logging configuration that is failing because of the
systemd configuration, or are you saying that if the systemd
configuration is updated *and* a logging stanza is added it would log to
this file?

I would e xpect the kdc to log to /var/log/auth.log out of the box,
which I find intuitive.

--Sam

[Karl-Philipp Richter (krichter722)]

> Are you seeing logging configuration that is failing
No, I just didn't think about syslog - maybe add a comment to the default `kdc.conf` that logging to syslog is the default. I'm closing as invalid because I didn't think through my request.

> I would e xpect the kdc to log to /var/log/auth.log out of the box,
which I find intuitive.
Agreed.