Re: Sporadic superfluous successful exits

[Aki Helin]

Jim Meyering <address@hidden> wrote:

> Aki Helin wrote:
> > For some reason Grep appears to occasionally exit with 0 even when there
> > was no match. This could also be bug Bash, but I wasn't able to reproduce
> > this with other programs, and the failure seems to be more common with
> > some patterns, or pairs of a pattern and an input, which would suggest
> > that the issue is in Grep.
> > [..]
>
> Can you reproduce that on more than one system?
>
> With such low frequency, I would suspect your system's RAM or other
> hardware.  I had a system that was 100% reliable for about six years,
> but then a few of the big capacitors near the CPU began (very slowly)
> to bulge and even to leak a little.  By the time 5 or 6 were bulging,
> I began to see errors and the occasional crash, usually only accompanying
> heavy disk or network activity.

Yes, this happens on several computers. I also suspected hardware issues
at first, but this seems to depend too much on what the software does, 
and there have been no issues apart from this on any of the machines.


> I've started one of your loops on a debian unstable system using
> grep-2.10 and zsh.  I will let it run for a few hours.

I left several loops running on several equal machines overnight to get
some more data. The machines are running 64-bit Debian stable and have
Atom CPUs, so they're a bit slower than typical desktops.

Machine 1, Bash, Grep 2.6.3
 - Loop 1: 1 date
 - Loop 2: 4 dates
 - Loops 3 and 4 reading from stdin: 0 dates

Machine 2, Dash, Grep 2.6.3
 - Loop 1: 0 dates
 - Loop 2: 1 segfault (will drop core next time if this happens again) 

Machine 3, Bash, Grep 2.10
 - Loop 1: 5 dates
 - Loop 2: 6 dates
 - Loop 3: 3 dates
 - Loop 4 reading from stdin: 0 dates

Machine 4, Bash, Grep 2.10 compiled with Clang & AddressSanitizer
 - Loops 1, 2 and 3: 0 dates

Machine 5, Zsh, Grep 2.6.3
 - Loops 1, 2 and 3: 0 dates

I also had a few similar loops running in Bash comparing two files with
cmp, but all return values stayed nonzero as expected.


-- 
Aki Helin