the use of the & sign in the ifconfig commad

tecsoftware · 04-03-2015, 04:09 AM

I found this script (part presented here) in the /etc/cron.hourly directory.

ifconfig $i up& (the $i in the do loop is either, lo (loopback), eth0 or eth1).

I know this turns the connection "on", but what effect is the & sign?

pan64 · 04-03-2015, 04:13 AM

& will put the process in the background, that means the cron will not wait for it any more.

rtmistler · 04-03-2015, 07:59 AM

Exactly what pan64 said.

But what does the script do next? Does it expect to use the network it just raised up? Because it may not yet be up, or never be up if circumstances do not allow. So the script is not blocked, but hopefully the script is checking status to determine if the network has connected.

tecsoftware · 04-03-2015, 11:27 PM

I forgot about the background use of the &. Amazing how things get loss in the mind.

the command is part of a virus I found. IN "hourly" the Ethernet is raised along with local loop.

IN "cron.minute", multiple messages are sent every second, the overload shuts things down.

I was wondering why cron on Linux has these monthly, weekly and hour directories rather than the just the crontabs in the original unix systems? What would happen if they (month, week, etc,) were removed? or just remove the place holder.

astrogeek · 04-04-2015, 12:19 AM

Quote:

Originally Posted by tecsoftware

the command is part of a virus I found. IN "hourly" the Ethernet is raised along with local loop.

IN "cron.minute", multiple messages are sent every second, the overload shuts things down.

I was wondering why cron on Linux has these monthly, weekly and hour directories rather than the just the crontabs in the original unix systems? What would happen if they (month, week, etc,) were removed? or just remove the place holder.

Well, that does not sound like a "virus", but just like a compomised system being exploited as a spam bot.

You really need to remove that system from network visibility immediately and fix whatever is going on with it.

Cron is really just cron... the hourly, daily and monthly are just convenience scripts that you can use to run jobs according to your own needs. It isn't so much a Linux thing as just some default choices made by the distro, which you should always reconfigure to suite your actual requirements.