How i can do a shell script to know if my connection is up on ubuntu

Question

I'm very low with shell scripts..

I need to check with a cron (no problem for this) if my connection is up. If it isn't, i want to call some scripts to reconnect.

I was thinking about using grep and ping to some site (or ip), then check the returned string.

Then call my command:

sudo pppd call speedtch

I need a clue thanks! Or there are better methods to do this?

Since my call need sudo, there's a batch way to call it without password input?

Answer 1

pinging works well, use this command line:

if ping -W 5 -c 1 google.com >/dev/null; then
    echo "Internet is up."
fi

This uses the following command line arguments to ping:

• -W 5: Time out waiting for a response after five seconds.
• -c 1: Only send one ping request. Default of most ping implementation is to send unlimited packages.
• Also the output of ping is redirected to /dev/null to avoid useless mails from cron.

As for your sudo question, you can configure that in the sudoers file.

Use the following line in sudo:

fromuser     ALL=(root) NOPASSWD: /usr/bin/mycommand

You'll need to replace the following strings:

• fromuser: Replace with the user who runs the cronjob
• /usr/bin/mycommand: Replace with the path of the command you want to execute

With this configuration the user "fromuser" will always be able to execute /usr/bin/mycommand without entering a password. You'll want to be careful with that of course for security reasons.