What is the difference between letting nohup append to 'nohup.out' and explicitly redirecting it to a file?

Question

Consider the following scenario:

tail.sh:

#!/bin/bash
tail -f test.txt

invoke.sh:

#!/bin/bash
nohup ./tail.sh &

invoke_explicitredirect.sh:

#!/bin/bash
nohup ./tail.sh > out.log &

Running both in a terminal has the same effect:

• I regain control of the terminal after running ./tail.sh
• No output from tail appears on the terminal

However, when running it using ssh (e.g. ssh <user>@<hostname> "<script>"):

• invoke_explicitredirect.sh returns control to ssh (and terminates)
• invoke.sh hangs until I send a SIGINT

man nohup states that nohup will automatically redirect output to 'nohup.out' if possible:

If standard output is a terminal, append output to 'nohup.out' if possible, '$HOME/nohup.out' otherwise.

What is the difference between letting nohup append to nohup.out and explicitly redirecting the output?

Answer 1

Standard output is not a terminal when you launch the command remotely through ssh. Use the -t option with ssh to get the same behavior with both of your commands.

More details on ssh and nohup: http://snailbook.com/faq/background-jobs.auto.html (taken from the wiki page: https://en.wikipedia.org/wiki/Nohup)