CODEWITHSUNDEEP
linuxbashraspberry-pi
user1944429
user1944429

Reputation:

Why won't my bash script run correctly?

I have a simple script, that works fine in the terminal, but not in init.d scripts or crontab. I'm working on a raspberry pi.

Is there a rule to writing scripts that run in the background?

This is my script:

 #!/bin/bash
 while true; do echo "ALIVE" | sudo nc -l -p 80; done

Upvotes: 0

Views: 460

Answers (2)

Michael Jaros
Michael Jaros

Reputation: 4681

  1. Cron scripts defined in /etc/crontab, /etc/cron.d or via crontab -e may run as a user other than root. All permissions (e.g. on logfiles) and authorization information (in your case sudoers) must be set accordingly.

  2. If they do not contain a Shebang line, cron scripts may run in a different shell, depending on the user the script is running as (see the shell set in /etc/passwd). The shell can also be overridden via SHELL variable in a crontab. This is not relevant for the OP's script.

  3. The shell running init.d and cron scripts may be using a different environment. Most notably the PATH may be different, so it is recommended to use absolute paths only or set the PATH as needed.

Upvotes: 1

piojo
piojo

Reputation: 6723

  1. The user running the script must be able to sudo. Configure this with the visudo command.

  2. You should check for output/errors. You can do that by changing it to:

    while true; do echo "ALIVE" | sudo nc -l -p 80 &>/var/log/netcat-test.log; done

Note that you should write the log to a place where that user definitely has access, and a directory that already exists. But this will trash your disk, due to writing lots and lots of logs. I suggest adding a delay:

 while true; do echo "ALIVE" | sudo nc -l -p 80 &>>/var/log/netcat-test.log; sleep 30; done
  1. You should check that the script is started at all. Add echo Script started >> the-log-file; date >> the-log-file. If the script is not starting, make sure it is marked as executable. If the script IS starting, make sure the script is not causing the system to crash--does the system need this script to return? Because it is not currently a background daemon. It does not ever finish, nor does it return control to the shell. Try replacing while true with for count in 1 2 for testing, to execute just twice.

Upvotes: 0

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