How to run a script in background (linux openwrt)?

Question

I have this script:

#!/bin/sh
while [ true ] ; do
    urlfile=$( ls /root/wget/wget-download-link.txt | head -n 1 )
    dir=$( cat /root/wget/wget-dir.txt )
    if [ "$urlfile" = "" ] ; then
        sleep 30
        continue
    fi

    url=$( head -n 1 $urlfile )
    if [ "$url" = "" ] ; then
        mv $urlfile $urlfile.invalid
        continue
    fi

    mv $urlfile $urlfile.busy
    wget -b $url -P $dir -o /www/wget.log -c -t 100 -nc
    mv $urlfile.busy $urlfile.done
done

The script basically checks for any new URLs at wget-download-link.txt for every 30 seconds and if there's a new URL it'll download it with wget, the problem is that when I try to run this script on Putty like this

/root/wget/wget_download.sh --daemon

it's still running in the foreground, I still can see the terminal output. How do I make it run in the background ?

Humanism

You can use the & operator at the end of your command to run it in the background. – Pippin

Answer 1

Try this:

 nohup /root/wget/wget_download.sh >/dev/null 2>&1 &

It will go to the background so when you close your Putty session, it will be still running, and it won't send messages to the terminal.

Wealthy

although your process will start in background but still OP will see the output from script on terminal. – Fauna

The complete command should be : nohup /root/wget/wget_download.sh >/dev/null 2>&1 & – Wealthy

I hadn't write it right the first time, so I edited it to add the /dev/null 2>&1. It was my fault. – Wealthy

The accepted answer should be the (command) & solution. There is no nohup on OpenWrt see this: bitzof.me/doku.php?id=electronics:wr703n:nohup – Hummocky

Answer 2

In OpenWRT (before 2023) there is neither nohup nor screen available by default, so a solution with only builtin commands would be to start a subshell with brackets and put that one in the background with &:

(/root/wget/wget_download.sh >/dev/null 2>&1 )&

you can test this structure easily on your desktop for example with

(notify-send one && sleep 15 && notify-send two)&

... and then close your console before those 15 seconds are over, you will see the commands in the brackets continue execution after closing the console.

Jara

Just leaving this here, it's 2023, opkg has nohup: opkg install coreutils-nohup – Caz

Answer 3

The following command will also work:

((/root/wget/wget_download.sh)&)&

This way you don't have to install the 'nohub' command in the tight memory space of the router used for OpenWrt.

I found this somewhere several years ago. It works.

Vixen

could you explain why we need two &? – Gain

@AllanRuin There exist no reasons to have two &s. – Underline

Answer 4

https://openwrt.org/packages/pkgdata/coreutils-nohup

opkg update
opkg install coreutils-nohup
nohup yourscript.sh &

Thingumajig

Answer 5

The &at the end of script should be enough, if you see output from the script it means, that stdout and/or stderr is not closed, or not redirect to /dev/null

You can use this answer:

How to redirect all output to /dev/null

Ibbison

Answer 6

I am using openwrt merlin and the only way to get it working was using the crud cron manager[1]. Nohub and screen are not available as solutions.

cru a pinggw "0 * * * * /bin/ping -c 10 -q 192.168.2.254"

works like charm

[1][https://www.cyberciti.biz/faq/how-to-add-cron-job-on-asuswrt-merlin-wifi-router/]

Hazaki

Answer 7

You can use nohup.

nohup yourscript.sh

or

nohup yourscript.sh &

Your script will keep running even if you close your putty session, and all the output will be written to a text file in same directory.

nohup is often used in combination with the nice command to run processes on a lower priority.

nohup nice yourscript.sh &

See: http://en.wikipedia.org/wiki/Nohup

Arrangement

Answer 8

For busybox in Openwrt Merlin system, I got a better solution which combined cru and date command

cru a YOUR_UNIQUE_CRON_NAME "`date -D '%s' +'%M %H %d %m *' -d $(( \`date +%s\`+2*60 ))` YOUR_CMD_HERE"

which add a cron job running 2 minutes later, and only run once.

Inspired by PlagTag's idea.

Lowboy

Answer 9

In another way these code would tried:

ssh [email protected] "/jffs/your_script.sh &"

Simple and without any programs like nohup screen...
(BTW: worked on Asus-Merlin firmware)

Lunge