how to create script for network restart? thx

hkcyber · 04-14-2019, 09:17 PM

Dear All

i'm newbie on script,i looking for how to create script then run the command <cat/proc/net/arp> if the 'HW address' show <incomplete>, then run <sudo ifconfig eth0 down> and <sudo ifconfig eth0 up> ,thx

BW-userx · 04-14-2019, 09:57 PM

have you figured out how to do this on the command line?
line 2 : if yes, then put the commands in a schipt to automate it.
if no, then figure out how to do this on the command line, then go to line 2, and complete it.

berndbausch · 04-14-2019, 10:15 PM

Quote:

Originally Posted by hkcyber

Dear All

i'm newbie on script,i looking for how to create script then run the command <cat/proc/net/arp> if the 'HW address' show <incomplete>, then run <sudo ifconfig eth0 down> and <sudo ifconfig eth0 up> ,thx

To check if the command cat /proc/net/arp outputs the string incomplete, you can do this:

Code:

if cat /proc/net/arp | grep -q incomplete
then 
    do whatever you want to do in this case
fi

This means:

the output of the cat command goes into a pipe
the grep command gets its input from the pipe. I.e. it gets the output of the cat command.
the grep command checks if the string incomplete appears in its input
if yes, the if condition is true, and the code between then and fi is executed.
You should probably put the ifconfig command there.
if not, the if condition is false, and the code between then and fi is skipped
the -q option ("quiet") tells grep not to output anything

Rather than ifconfig, I suggest using the ip command. It's up-to-date and can handle more networking features that the aging ifconfig:

Code:

sudo ip link set eth0 up

Some distros don't deploy ifconfig anymore.

hkcyber · 04-14-2019, 11:54 PM

Quote:

Originally Posted by berndbausch

To check if the command cat /proc/net/arp outputs the string incomplete, you can do this:

Code:

if cat /proc/net/arp | grep -q incomplete
then 
    do whatever you want to do in this case
fi

This means:

the output of the cat command goes into a pipe
the grep command gets its input from the pipe. I.e. it gets the output of the cat command.
the grep command checks if the string incomplete appears in its input
if yes, the if condition is true, and the code between then and fi is executed.
You should probably put the ifconfig command there.
if not, the if condition is false, and the code between then and fi is skipped
the -q option ("quiet") tells grep not to output anything

Rather than ifconfig, I suggest using the ip command. It's up-to-date and can handle more networking features that the aging ifconfig:

Code:

sudo ip link set eth0 up

Some distros don't deploy ifconfig anymore.

It work! Thankyou

jenniT · 05-04-2019, 04:16 AM

not understand

BW-userx · 05-04-2019, 09:46 AM

Quote:

Originally Posted by jenniT

not understand

OK: steps:
Objective:

Quote:

Originally Posted by jenniT

create script then run the command <cat/proc/net/arp>
if the 'HW address' show <incomplete>, ????
then run <sudo ifconfig eth0 down>
and <sudo ifconfig eth0 up>

Are you sure that is all you want to do?
First work it out in a terminal to check your commands and out put.

Code:

$ cat /proc/net/arp
  1                  2         3             4                  5         6
IP address       HW type     Flags       HW address            Mask     Device
1xx.xx.xx.x      0x1         0x2         9c:1c:12:c9:7a:f0     *        wlan0

that requires you use something to get the HW address. awk in this case

Code:

$ cat /proc/net/arp | awk 'FNR==2 { print $4}'
9c:1c:12:c9:7a:f0

put that into a variable then check to see if it is empty or not.

Code:

[ -n "$(cat /proc/net/arp | awk 'FNR==2 { print $4}')" ]] && { echo "up" ; }
up

put that and the commands to bring down then up your net.

Code:

#!/bin/bash
#if not , or is empty then bring down then up net
[[  -z "$(cat /proc/net/arp | awk 'FNR==2 { print $4}')" ]] && { sudo ifconfig eth0 down ; sudo ifconfig eth0 up ; }

will it do what you want? I do not know, I only completed the steps in your objective, and I do not know your output for the cat command.

Though, I'd say that @berndbausch knows more about the nic interphase output for eth0 because he says to use grep, and suggests to use the 'ip' commands. They supersede ifconfig.

what just hold on : jenniT is not even the OP...

TB0ne · 05-05-2019, 10:29 AM

Quote:

Originally Posted by hkcyber

Dear All
i'm newbie on script,

A 'newbie', who's been here for TWELVE YEARS???

Quote:

i looking for how to create script then run the command <cat/proc/net/arp> if the 'HW address' show <incomplete>, then run <sudo ifconfig eth0 down> and <sudo ifconfig eth0 up> ,thx

Read the LQ Rules about text-speak, and not using it. And since you know the steps, have 12 years experience with Linux, and have access to the thousands of bash-scripting tutorials you can find online, show us what YOU have done/tried of your own; read the "Question Guidelines".

We are happy to help, but you are just asking people to write scripts for you, and showing no effort of your own.