From: A. Mahendra Rajah (Mahendra.Rajah@URegina.CA)
Date: Tue Apr 01 2003 - 11:30:38 EST
I asked the following question a few days ago:
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We could not telnet, ftp, ssh or LAT into our Alphaserver
DS20 (Tru64 v5.1A + Pkit3) all day today. Xwindows
connections worked.
In the /var/adm/syslog.dated/daemon.log file and at the
console, the following message got displayed frequently:
<date> <machine> inetd[859]: accept: Operation would block
What would cause this error to show up and why couldn't
we make telnet, ssh or LAT connections to this host?
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I received only one reply, from the ever reliable Dr. Tom
Blinn. Tom said:
If you read the accept(2) reference page, you will find
this (or similar) text:
[EWOULDBLOCK] The socket is marked nonblocking, and no
connections are present to be accepted.
The standard string name for "EWOULDBLOCK" is "Operation
would block"; if the current errno is the EWOULDBLOCK
value and you use "perror()" to print an error string,
you get that string.
This is probably (but not necessarily) due to some
resource inside the kernel being exhausted. After all,
accept() becomes a syscall pretty quickly, and it's the
kernel that returns the EWOULDBLOCK error code to the
libc code, which returns it to the application. Either
it's a bug in the kernel, or it's a predictable condition
based on something that was happening in your network or
your system at the time. Either way, that's about as
much as I can tell you.. I can't tell you (without a
close examination of the kernel code that get's invoked
for an accept() which is NOT in my personal area of
expertise) what condition causes the error to be
returned; I could probably find someone who could point
me to the right place in the IP stack to look, but it's
not something I know particularly well..
Thank you Tom.
HP support pitched in and confirmed that this error was
the remanant of some failed port scan attempt. Rebooting
the machine cleared it.
-- mahendra
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A. Mahendra Rajah Email: Mahendra.Rajah@URegina.CA
Tru64 UNIX Systems Manager Phone: (306) 585-4496
Dept. of Computing Services FAX: (306) 337-2324
University of Regina,
Regina, Sask., S4S 0A2
Canada.
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