On 2021/06/29 17:55, Vincent Lefevre wrote:
On 2021-06-29 13:30:53 -0700, L A Walsh wrote:
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No. the pwd utility has had its stdout redirected by its
parent, "the shell". Since the faulty redirection was done by parent,
is the error in the child or the parent?
The redirection is not faulty. /dev/full is a valid file, with
permissions to write to it. But it behaves as a full file system
(like what may happen with any normal file system), i.e. yielding
an ENOSPC error when writing to it.
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Sorry, difference of terminology. By faulty, I mean that the
parent application, (bash in this case), chose to redirect to
a location that was "full". I.e. it is a "faulty redirection",
in that it is redirected to a destination that will cause a
"fault" or "failure".
In a similar way, I made sure my /dev/zero was read only (AFAIK, it is
only for generating a stream of binary zeros), but I am not aware of
any useful effect of writing to it (unless it be the equivalent of
/dev/null, but I can use /dev/null for writing to, so at least for
now, I made my /dev/zero read-only. Then I ran both pwd and 'cd' with
output redirected to the read-only /dev/zero. Both failed and their action
was not performed -- verifiable by noting that "cd ~ >& /dev/zero" doesn't
change to my home directory.
Anyway, it is the parent that is directed the output to a location that
won't work as an output destination. In my example with >/dev/zero, I
got a permission denied from the parent process. If I had a /dev/full
I'd expect the same thing -- an error message from bash when it closes
the pipe to /dev/full.
the 'pwd' application cannot know or respond to the error, since the output
can be buffered and 'pwd' would exit, and the output would possibly be
closed
for pwd upon its exit -- unless the output was still open in the parent, and
only upon the final close, would you be guaranteed to get an error from the
'close' operation as the buffers would fail to find space (on /dev/full).
So there's no way to guarantee that 'pwd' would ever see any error condition
that I can tell.
