Re: NIS exhausts system resources

Terry Lambert writes:
 > Dan Pelleg wrote:
 > > I'm not sure I understand this. First, if the server is down when the
 > > client boots, this will stop the client's boot sequence (or at least slow
 > > it significantly down).
 > 
 > Not really.  All it will do is cause requests for information
 > normally contained in NIS to fail, following some delay (for
 > example, for gethostbyaddr(), if the hosts file is NIS
 > distributed, it will cause a 3 minute delay on reverse address
 > resolution, before failing back to returning the IP address).
 > 
 > For getpwnam(), the lookup will simply fail completely, after
 > the NIS server is judged to no be responding, which will only
 > occur after a connection attempt fails after a certain amount
 > of time.
 > 

This sounds plausible, thanks.

However, In the past, when configuring NIS for the first time, I did see
the machine go unresponsive on me as soon as I did a "domainname foo". This
was probably at a time when the server wasn't set up correctly. But why
would that immediately cause high resource usage? There shouldn't be any
name or user lookups taking place. This is a very quiet machine - I don't
think it was running more than very lightly loaded postfix and sshd at the
time, and I was the only user logging in. Name lookups, by the way, should
not go out anyway - the machine is running its own named.

 > 
 > > sshd isn't given a chance to start.
 > 
 > I mistakenly understood your original posting to say that it
 > "was the sshd problem reported here several times"; missed the
 > "NOT"; sorry.
 > 
 > > The only sign of life from the machine at this point is ICMP replies
 > > and the sound of the grinding disk (probably syslogd).
 > 
 > You also said there was another "sign of life":
 > 
 > | kernel: file: table is full
 > | syslogd: /dev/console: Too many open files in system
 > | rpcbind: rpc: failed to open /etc/netconfig
 > | rpcbind: warning: /etc/hosts.allow, line 23: cannot open /etc/hosts.allow:
 > |    Too many open files in system
 > 

These are lines I extracted from the log files after the machine went back
up (I turned on the NIS server and rebooted the client). Sorry if this
wasn't clear.

 > The "file: table is full" and the "Too many open files in system"
 > can be fixed by the method I describe: recompile your kernel with
 > a larger MAXUSERS.
 > 
 > As far as the "too many open files", there are two possible
 > causes.  The first is that so many things are piled up waiting
 > for NIS, that there are *really* "too many open files".  Rasing
 > the MAXUSERS raises the definition of "too many".  Raise it high
 > enough, and the problem will "go away" (e.g. if "too many" is "10",
 > you will have problems when you try to open 50 files, but if "too
 > many" is "100", you won't have that problem).
 > 
 > 
 > The second cause is probably that the "/etc/hosts.allow" file is
 > opened, the file read, the NIS checked, and then the file is
 > closed.  If you changed the order of operation so that the file
 > was not held open while NIS was being checked, then you would not
 > have the problem, e.g.:
 > 
 > 	Fails			OK
 > 	Open A			Open A
 > 	Read A			Read A
 > 	Open B			Close A
 > 	<wait a long time>	Open B
 > 	Close B			<wait a long time>
 > 	Close A			Close B
 > 
 > 	<2 files held open>	<1 file held open>
 > 
 > ... in other words, if you divide the number of open files by 2,
 > then maybe if (2*X > "too many"), just (X < "too many").
 > 
 > Make sense?
 > 

Yes, it does.

 > 
 > > Next, this is a wimpy machine. 233Mhz processor and 64MB of RAM. I don't
 > > know if that matters or not, but I'm not confident of my ability to tweak
 > > the memory usage on it.
 > 
 > 	cd /usr/src/sys/i386/conf
 > 	cp GENERIC MYKERNEL
 > 	vi MYKERNEL			# Increase MAXUSERS by 2-3 times
 > 	config MYKERNEL
 > 	cd ../compile/MYKERNEL
 > 	make depend
 > 	make
 > 	make install
 > 

I was going to say "I have my MAXUSERS set to 0, which is still 0 after
multipying by 3". But checking the config file it turns out that it doesn't
have MAXUSERS defined at all. And neither does GENERIC (from a copy of
which I probably started my own config file) nor NOTES. What is the
equivalent of MAXUSERS on -CURRENT?