bug#30993: OpenSSH sshd killed by Shepherd 0.4.0

[Leo Famulari]

Since the update to Shepherd 0.4.0, I've found that OpenSSH's sshd is
killed almost immediately after it starts with signal 15. I confirmed
the issue started with the Shepherd upgrade by bisecting our Git
history.

I can reproduce the issue from commit
b6beda1d6b9093a8493b5c3cde33ed522242c451 (gnu: Add botan.).

One interesting tidbit is that the PID file '/var/run/sshd.pid' is not
created anymore. And if I create an empty PID file by hand, it is
removed after trying to start the ssh-daemon service. Also, the sshd
user's home '/var/run/sshd' does not exist, and is similarly removed if
it does exist.

I ran the OpenSSH system test `make check-system TESTS=openssh` and it
failed when it could not find the PID file. It passed on another
non-GuixSD machine. The failing machine is relatively slow and lacks
KVM: a ThinkPad x200s.

After boot, trying to start the service again with `herd start
ssh-daemon` gives the same result.

I modified the sshd invocation to print some debug output ('-d -E
/tmp/sshd.log') and this is what it shows:

------
debug1: sshd version OpenSSH_7.6, OpenSSL 1.0.2o  27 Mar 2018
debug1: private host key #0: ssh-rsa SHA256:REDACTED
debug1: private host key #1: ssh-dss SHA256:REDACTED
debug1: private host key #2: ecdsa-sha2-nistp256 SHA256:REDACTED
debug1: private host key #3: ssh-ed25519 SHA256:REDACTED
debug1: 
rexec_argv[0]='/gnu/store/az7vib8gk16fybhshh5xpkljmgxyrs4k-openssh-7.6p1/sbin/sshd'
debug1: rexec_argv[1]='-D'
debug1: rexec_argv[2]='-d'
debug1: rexec_argv[3]='-E'
debug1: rexec_argv[4]='/tmp/sshd.log'
debug1: rexec_argv[5]='-f'
debug1: rexec_argv[6]='/gnu/store/miy7xg5j4fg3mn04mcl27awmcl6s97ss-sshd_config'
debug1: Set /proc/self/oom_score_adj from 0 to -1000
debug1: Bind to port 22 on 0.0.0.0.
Server listening on 0.0.0.0 port 22.
debug1: Bind to port 22 on ::.
Server listening on :: port 22.
Received signal 15; terminating.
------

My system configuration file, the shepherd log messages, and the OpenSSH
system test logs are attached. Any ideas?

shepherd.log
Description: Text document

system.scm
Description: Text document

check.log
Description: Text document

signature.asc
Description: PGP signature