I put a python program in cron and it starts behaving different.

#!/usr/bin/env python3

import sys
import os
import stat
from os import isatty
#https://python-forum.io/thread-10606.html



print("stdin")
print("isatty", isatty(sys.stdin.fileno()) )

mode = os.fstat(0).st_mode
print("ISFIFO", stat.S_ISFIFO(mode) )
print("ISREG", stat.S_ISREG(mode) )
print("ISLNK", stat.S_ISLNK(mode) )

print("ISDIR", stat.S_ISDIR(mode) )
print("ISCHR", stat.S_ISCHR(mode) )
print("ISBLK", stat.S_ISBLK(mode) )
print("ISSOCK", stat.S_ISSOCK(mode) )

print("done")

Apparently, using istty isn’t reliable indicator that you are getting redirected data. I guess I can accept that, since cron intuitively doesn’t have a terminal. So what is the stdin of a Linux Daemon?

This doesn’t answer it:
https://unix.stackexchange.com/questions/278105/what-are-the-default-stdin-and-stdout-of-a-child-process

In fact, I can’t Google the answer. But I tried checking all the possible stat tests. And when I ran it in cron…

stdin
isatty False
ISFIFO True
ISREG False
ISLNK False
ISDIR False
ISCHR False
ISBLK False
ISSOCK False
done

I can accept a lot of things. But why is a cronjob, which I assume inherits stdin from cron, have a stdin that python considers a fifo pipe? This is the very logic, I would’ve used to check if stdin was redirected from output of another process.

This is a fantastic failure, b/c it is very strange.