python - prevent IOError: [Errno 5] Input/output error when running without stdout

Question

I have a script that runs automatically on server through cronjob and it import and run several other scripts. Some of them use prints, which naturally creates `IOError: [Errno 5] Input/output error` because the script runs without any SSH / terminal connected, so there's no proper stdout setup. There are lots of questions about this subject but I couldn't find anyone that actually solve it, assuming I can't remove the print or change the executed scripts. I tried several things, including: ``` class StdOut(object): def __init__(self): pass def write(self, string): pass sys.stdout = StdOut() sys.stderr = StdOut() ``` and ``` from __future__ import print_function import __builtin__ def print(*args, **kwargs): pass __builtin__.print = print ``` But none of it works. I assume it only affect the module itself and not the modules I import / run later. So how can I create a stub stdout that will affect all modules in the process? Like I said, I don't want to change the scripts that are exec…

Accepted Answer

Modifying the builtin or changing `sys.stdout` should work (except for subprocesses—but you ruled those out) as long as you do it early enough. If not, though, there's a lower level trick that's much easier:

run your python scripts with I/O redirection that discards output:

```
python foo.py >/dev/null 2>&1
```

(assuming Unix-y scripts, as implied by "cron" in the question)

or, redirect file descriptors 1 and 2 (same idea as above, but done within your Python startup rather than as part of the cron-invoked command):

```
import os
fd = os.open(os.devnull, os.O_RDWR)
# NB: even if stdin is closed, fd >= 0
os.dup2(fd, 1)
os.dup2(fd, 2)
if fd > 2:
    os.close(fd)
```

(this particular bit of code has the side effect of making /dev/null act as stdin, if all descriptors were closed). [Edit: I started with `with open(...)` and then switched to `os.open` and did not test the final version. Fixed now.]

All that said, a good cron really should have stdout and stderr connected somewhere, and should email the output/error-output to you. Not all cron versions are this nice though.

python - prevent IOError: [Errno 5] Input/output error when running without stdout

Solution

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