SCO Unix TCP/IP and NFS FAQ

This article is from a FAQ concerning SCO operating systems. While some of the information may be applicable to any OS, or any Unix or Linux OS, it may be specific to SCO Xenix, Open There is lots of Linux, Mac OS X and general Unix info elsewhere on this site: Search this site is the best way to find anything.

How do I know if I have enough streams buffers for TCP/IP and/or NFS on SCO Unix?

This is an ancient post with no relevance to modern systems.

In OpenServer Release 5, streams buffers are among the data structures allocated dynamically by the kernel, and so in general you will never need to tune them because the system will allocate more if it's running short. Note also that OSR5 does away with the 80% and 90% (default) low and medium priority limits.

Under Xenix, use the program sw (stream watch); it will provide a dynamic display of the current and historical usage of various stream buffers. Under Unix, you can use the crash command; the subcommand to use is strstat. Under TCP/IP for Unix, you can also use the netstat -m command. Finally, u386mon, available as tls012, provides similar functionality; it will not work for Xenix.

Generally, you should set each class of streams buffer to be 30-40% higher than the maximum usage you see, because by default the kernel will usually only use 80% of the buffers you have allocated (the rest are reserved for high-priority use, and this percentage is tunable; there is probably no reason why you can't set STRLOFRAC to 95 and STRMEDFRAC to 97). Leave your system running and under typical use for as long as practicable (at least a few days, if at all possible), and then use one of the tools mentioned above to check the status of your streams buffers. These tools list the configured limits for each class of buffers, the maximum number of each class used since the system was rebooted, and also how many times an allocation request for a given class has failed due to lack of available buffers. It's usually not a bad idea to tune the number of each class of buffer, because if you've allocated far more than is needed you're wasting memory and if you've underallocated, you may experience problems. For more information, consult your System Administrator's Guide.

Aside from anything else that might cause "out of streams resources" messages, I've seen this happen when someone added (for example) a 25 user license and didn't take advantage of the offer to tune the system for the additional users. See this Out of stream resources post at comp.unix.sco.misc for an example.


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