Running Complex Commands with sudo
If you use sudo to run commands as root, you've probably run into “permission denied” problems when only part of a pipeline or part of a command is running with root permissions.
This fails with “permission denied” because the file is writable only by root:
$ echo 12000 > /proc/sys/vm/dirty_writeback_centisecs
But, this fails too:
$ sudo echo 12000 > /proc/sys/vm/dirty_writeback_centisecs
Why? The /bin/echo program is running as root, because of sudo, but the shell that's redirecting echo's output to the root-only file is still running as you. Your current shell does the redirection before sudo starts.
The solution is to run the whole pipeline under sudo. There are a couple ways to do it, but I prefer:
echo "echo 12000 > /proc/sys/vm/dirty_writeback_centisecs" | sudo sh
That way, I can type everything before the pipe character, and see what I'm about to run as root, then press the up arrow and add the | sudo sh to do it for real. This is not a big deal for short, obvious pipelines, but when you're building up a more complicated command as root, it's safer to look at it first before you run it.
Webinar: 8 Signs You’re Beyond Cron
On Demand NOW
Join Linux Journal and Pat Cameron, Director of Automation Technology at HelpSystems, as they discuss the eight primary advantages of moving beyond cron job scheduling. In this webinar, you’ll learn about integrating cron with an enterprise scheduler.View Now!
|Non-Linux FOSS: Vienna, Not Just for Sausages||Jun 02, 2015|
|June 2015 Issue of Linux Journal: Networking||Jun 01, 2015|
|June 2015 Video Preview||Jun 01, 2015|
|My Humble Little Game Collection||May 28, 2015|
|New Linux Based OS Brings Internet of Things Closer to Reality||May 27, 2015|
|Non-Linux FOSS: All the Bitcoin, None of the Bloat||May 26, 2015|
- Non-Linux FOSS: Vienna, Not Just for Sausages
- June 2015 Issue of Linux Journal: Networking
- New Linux Based OS Brings Internet of Things Closer to Reality
- Dr Hjkl on the Command Line
- Initializing and Managing Services in Linux: Past, Present and Future
- Using Hiera with Puppet
- My Humble Little Game Collection
- Gartner Dubs DivvyCloud Cool Cloud Management Vendor
- Infinite BusyBox with systemd
- Goodbye, Pi. Hello, C.H.I.P.