Redirecting stdout & stderr from background process

Question

I have a script called foo that runs the program a.exe and sends the timing statistics to a file, time.log

#!/bin/bash
date 1>> time.log
(time ./a.exe) 2>> time.log

This works if I run the script in the background of my terminal and keep my shell open until a.exe finishes, but if I run the script in the background and exit my terminal (a.exe takes a long time to run)

foo & 
exit

when I come back, a.exe has executed but the time statistics do not appear in my log file. Does anyone know why this is? Is there a way to get the timing statistics after I've closed the parent shell?

thanks

Answer 1

nohup foo &

When you exit your shell it sends a SIGHUP signal to all child processes, which by default kills them. If you want a process to continue executing even when the parent shell exits then you need to have it ignore the SIGHUP.

NAME

nohup -- invoke a command immune to hangups

SYNOPSIS

nohup utility [arg ...]

DESCRIPTION

The nohup utility invokes command with its arguments and at this time sets the signal SIGHUP to be ignored. If the standard output is a terminal, the standard output is appended to the file nohup.out in the current directory. If standard error is a terminal, it is directed to the same place as the standard output.

Answer 2

Since the question is tagged as bash as well, I quote from man bash

disown [-ar] [-h] [jobspec ...]
          Without  options,  each  jobspec  is  removed  from the table of
          active jobs.  If jobspec is not present, and neither -a  nor  -r
          is  supplied, the shell's notion of the current job is used.  If
          the -h option is given, each jobspec is not removed from the ta‐
          ble,  but is marked so that SIGHUP is not sent to the job if the
          shell receives a SIGHUP.  If no jobspec is present, and  neither
          the  -a  nor the -r option is supplied, the current job is used.
          If no jobspec is supplied, the -a option means to remove or mark
          all  jobs;  the  -r  option without a jobspec argument restricts
          operation to running jobs.  The return value is 0 unless a  job‐
          spec does not specify a valid job.

This comes in handy when you started a job but forgot to prefix it with nohup. Just do

disown -ah
disown -a