The Ping Hosts Service (1.5)

This page describes FOG 1.5.

See the 1.6 version of this page for FOG 1.6.

FOGPingHosts is the background service that answers one question for every host in your database: can the server reach it right now? Its verdict is what the Ping Status column on Host Management shows.

Despite the name, it never sends an ICMP echo request

The service does not “ping” a host the way ping at a command line does. It opens a TCP connection to port 445 (SMB) and records whether the connection succeeded, so a host that answers ping but does not listen on port 445 — most Linux hosts, or any Windows host with file and printer sharing turned off — is reported unreachable. That is working as designed on this version.

How it decides “up”

For every host, in order:

1. Resolve the host’s name through DNS.
2. Open a TCP connection to port 445, giving up after 2 seconds.
3. Record the resulting socket error number on the host. 0 means the connection succeeded.

Both the port and the timeout are fixed in the code — 1.5 has no setting for either, and no way to change them without editing ping.class.php.

What this means in practice

• “Is this host up?” really means “does this host accept SMB?” A Linux host, a Windows host with file and printer sharing off, and anything behind a host firewall are all permanently reported unreachable no matter how healthy they are.
• A refused connection still counts as reachable. If a host is powered on but nothing is listening on port 445, its kernel replies with a TCP reset. That is proof of life — only a machine that is on, on the network and routable from the server can send that reset — so it is recorded as up. A host that silently drops the connection instead (a firewall configured to drop rather than reject) looks identical to one that is switched off.
• Hosts are tested one at a time. Every unreachable host costs the full 2-second timeout before the next one is tried. On a fleet with any number of powered-off hosts, this adds up quickly against the sleep interval between cycles (PINGHOSTSLEEPTIME, 300 seconds by default), and the service can end up running continuously with stale answers.
• Only the latest verdict is kept. There is no “Last Successful Ping” field on this version — just the current Ping Status. “This host has been off for a month” and “this host went off ten minutes ago” look identical, because nothing records when a host was last seen reachable. (1.6 adds a Last Successful Ping / Last Client Check-In pair for exactly this reason — see the 1.6 version of this page.)

Settings reference

Setting	Category	Default
PINGHOSTGLOBALENABLED	FOG Linux Service Enabled	on
PINGHOSTSLEEPTIME	FOG Linux Service Sleep Times	300
PINGHOSTLOGFILENAME	FOG Linux Service Logs	pinghost.log
PINGHOSTDEVICEOUTPUT	FOG Linux Service TTY Output	/dev/tty3

There is no PINGHOSTPORT, PINGHOSTTIMEOUT, or PINGHOSTUSEICMP setting on this version — those are all 1.6 additions. The port and timeout are the 445 / 2 values hardcoded in ping.class.php.

With PINGHOSTGLOBALENABLED off, no host is ever pinged and Ping Status stays at whatever was last recorded.

FOG_HOST_LOOKUP does nothing on this version

The List All Hosts page has an FOG_HOST_LOOKUP setting on the configuration page, and long-standing advice says to untick it on fleets over about 250 hosts to keep the host list fast. On 1.5 that setting is read by the configuration page and by nothing else — it does not gate any behavior, so unticking it never sped anything up. (1.6 wires it up for real, to control whether the Ping Status column is shown.)

Troubleshooting

Every host shows unreachable. Start with DNS, not the port. The service looks hosts up by name, so it needs a DNS server your DHCP server updates, or entries in /etc/hosts. Test with:

getent hosts somehostname

If that fails, the ping cannot succeed regardless of what is listening on port 445.

A single host shows unreachable but you can reach it. Most likely a host firewall that silently drops the connection instead of refusing it — that looks identical to a host that is switched off, because nothing comes back at all. Allowing port 445 through that host’s firewall, even to a closed service, is enough to make it show as reachable (a refused connection still counts, as above).

Nothing is being pinged at all. Check PINGHOSTGLOBALENABLED, then the service log at /var/log/fog/pinghost.log (or wherever PINGHOSTLOGFILENAME points).

The service says it is not the FOG web server. FOG_WEB_HOST must resolve to an address on the machine running the service — this is the guard that stops a storage node from pinging your whole fleet.

Related

• Host Management
• FOG Client installation options
• Network and firewall requirements