sshd doesn't "re-read" it's configuration file, it restarts itself (refer to man sshd(8)), however, it shouldn't kill the child/connections if you sent the SIGHUP to the PARENT of them all. That is when you are talking about sshd that binds to port 22, as in the "usual" with Linux/FreeBSD/etc. [there are exceptions and sysadmin reasons why to follow the MacOSX type route]
HOWEVER MacOSX have launchd as the one that listens to and handles port 22 (from my 10.10.4 machine):
BlackYos:~ hvisage$ sudo lsof -i :22
Password:
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
launchd 1 root 57u IPv4 0xdb59a664e4b34941 0t0 TCP blackyos:ssh->hvs:39093 (ESTABLISHED)
launchd 1 root 58u IPv4 0xdb59a664e4b34941 0t0 TCP blackyos:ssh->hvs:39093 (ESTABLISHED)
launchd 1 root 62u IPv6 0xdb59a664c78cd671 0t0 TCP *:ssh (LISTEN)
launchd 1 root 66u IPv4 0xdb59a664c78d2e21 0t0 TCP *:ssh (LISTEN)
launchd 1 root 67u IPv6 0xdb59a664c78cd671 0t0 TCP *:ssh (LISTEN)
launchd 1 root 68u IPv4 0xdb59a664c78d2e21 0t0 TCP *:ssh (LISTEN)
ssh 1262 hvisage 3u IPv4 0xdb59a664e59313b1 0t0 TCP blackyos:51628->hvs:ssh (ESTABLISHED)
sshd 1272 root 4u IPv4 0xdb59a664e4b34941 0t0 TCP blackyos:ssh->hvs:39093 (ESTABLISHED)
sshd 1272 root 5u IPv4 0xdb59a664e4b34941 0t0 TCP blackyos:ssh->hvs:39093 (ESTABLISHED)
sshd 1274 hvisage 4u IPv4 0xdb59a664e4b34941 0t0 TCP blackyos:ssh->hvs:39093 (ESTABLISHED)
sshd 1274 hvisage 5u IPv4 0xdb59a664e4b34941 0t0 TCP blackyos:ssh->hvs:39093 (ESTABLISHED)
It is launchd that might need to be "restarted" on macosx, or told about different ports to listen on for sshd, as launchd will spawn a new sshd for each port 22 connection that comes in.
check the following:
BlackYos:~ hvisage$ sudo ps -ef |grep -i ssh
501 1263 1 0 6:46PM ?? 0:00.06 /usr/bin/ssh-agent -l
0 1272 1 0 6:46PM ?? 0:00.40 sshd: hvisage [priv]
501 1274 1272 0 6:46PM ?? 0:00.03 sshd: hvisage@ttys004
501 1262 570 0 6:46PM ttys001 0:00.05 ssh -v hvs
501 1303 1275 0 6:50PM ttys004 0:00.00 grep -i ssh
BlackYos:~ hvisage$
I've ssh'd to my router and back to demonstrate the issue, and you'll notice that the two processes are already "owned" by me.
Compare this to a Linux system (my roouter) where you'll notice the third "real" sshd that is owned by root:
hvisage@hvs:~$ ps -ef |grep -i ssh
root 4053 1 0 Jul11 ? 00:04:22 /usr/sbin/sshguard -i /var/run/sshguard.pid -l /var/log/auth.log -w /etc/sshguard/whitelist -a 40 -p 420 -s 1200
root 16244 30219 0 18:46 ? 00:00:00 sshd: hvisage [priv]
hvisage 16249 16244 0 18:46 ? 00:00:00 sshd: hvisage@pts/0
hvisage 16563 16250 0 18:52 pts/0 00:00:00 grep -i ssh
root 30219 1 0 Aug09 ? 00:00:00 /usr/sbin/sshd
hvisage@hvs:~$
Best Answer
In order to allow SSH incoming connections to your Mac, you need to enable Remote Login in Sharing Preferences pane.
Here’s a picture: