[SOLVED] Why do I have to use sudo before iwconfig when logged in as root in Debian 10?

Trent29 · 06-04-2020, 03:09 PM

iwconfig gives error message unless I use sudo command. I understand that this is normal if I'm logged in as a regular user, but it happens when I'm root as well. Why is Debian requiring me to use the sudo command for iwconfig when I'm logged in as root and how would I fix this?

Trent29 · 06-04-2020, 05:07 PM

Code:

user@debian:~$ iwconfig
bash: iwconfig: command not found
user@debian:~$ sudo iwconfig
[sudo] password for user: 
lo        no wireless extensions.

eth0    no wireless extensions.

wlan0    IEEE 802.11  ESSID:off/any  
          Mode:Managed  Access Point: Not-Associated   Tx-Power=off   
          Retry short limit:7   RTS thr:off   Fragment thr:off
          Encryption key:off
          Power Management:off
          
user@debian:~$ su
Password: 
root@debian:/home/user# iwconfig
bash: iwconfig: command not found
root@debian:/home/user# sudo iwconfig
lo        no wireless extensions.

eth0    no wireless extensions.

wlan0    IEEE 802.11  ESSID:off/any  
          Mode:Managed  Access Point: Not-Associated   Tx-Power=off   
          Retry short limit:7   RTS thr:off   Fragment thr:off
          Encryption key:off
          Power Management:off
          
root@debian:/home/user# cd /
root@debian:/# iwconfig
bash: iwconfig: command not found
root@debian:/# sudo iwconfig
lo        no wireless extensions.

eth0    no wireless extensions.

wlan0    IEEE 802.11  ESSID:off/any  
          Mode:Managed  Access Point: Not-Associated   Tx-Power=off   
          Retry short limit:7   RTS thr:off   Fragment thr:off
          Encryption key:off
          Power Management:off
          
root@debian:/#

michaelk · 06-04-2020, 05:30 PM

iwconfig command is not in a regular users path environment.

Using su still uses the regular users path but if using su - instead will switch to roots.

Using sudo will run the command as root using roots environment.

Crippled · 06-04-2020, 05:41 PM

Because the command line is counter intuitive gibberish. My advice for you is don't try to make sense of it because no one who is sane or not on drugs can.

astrogeek · 06-04-2020, 10:40 PM

As michaelk has pointed out, when you use su to become root, you are still using the environment of the regular user and that environment does not include the PATH to reach it (typically /sbin/iwconfig, may be different on your debian). Using su - (su followed by a dash) switches to the normal login environment of the user you are switching to, root if no other name is given.

From man su:

Code:

DESCRIPTION
       The su command is used to become another user during a login session. Invoked without a username, su
       defaults to becoming the superuser. The optional argument - may be used to provide an environment
       similar to what the user would expect had the user logged in directly.

Some people choose to not avail themselves of the added power and ease of use provided by the shell prompt which is an integral, necessary and intended feature of the underlying Unix-like design philospohy of GNU/Linux. You are always advised to understand how the system was intended to work (it is not difficult, and certainly not gibberish) and doing so will make your Linux experience much more enjoyable.

Users who have nothing useful to contribute should refrain from commenting.

Trent29 · 06-05-2020, 02:16 PM

Thanks for the great explanations.

So then, does using cd / only change the directory and not the environment, even though the prompt changes from root@debian:/home/user# to root@debian:/# ?

Code:

root@debian:/home/user# cd /
root@debian:/# iwconfig
bash: iwconfig: command not found
root@debian:/# sudo iwconfig
lo        no wireless extensions.

eth0    no wireless extensions.

wlan0    IEEE 802.11  ESSID:off/any  
          Mode:Managed  Access Point: Not-Associated   Tx-Power=off   
          Retry short limit:7   RTS thr:off   Fragment thr:off
          Encryption key:off
          Power Management:off
          
root@debian:/#

sevendogsbsd · 06-05-2020, 02:48 PM

Correct. You are simply changing the current directory; that doesn't affect the environment.

scasey · 06-05-2020, 02:49 PM

Quote:

Originally Posted by Trent29

Thanks for the great explanations.

So then, does using cd / only change the directory and not the environment, even though the prompt changes from root@debian:/home/user# to root@debian:/# ?
[

Yes. cd does not change the environment. Also cd by itself will switch to the logged in user’s home directory, which is /root for root, not /
cd - will change the environment and switch to the /root directory. You can see where you are with the pwd command...but again, which directory you’re in says nothing about the environment.

shruggy · 06-05-2020, 03:05 PM

When you issue a command without path it's searched in the current directory, then in directories pointed to by environment variable PATH.

When you change to the filesystem root (/), iwconfig is not there. So it's searched on PATH. PATH for regular users doesn't include /sbin directory where iwconfig is located.

When you gain root privileges via su or sudo -s, startup scripts for root (/etc/profile, /root/.profile, /root/.bashrc, etc.) are not executed. Those scripts among other things set environment. For the root user, they amend PATH so that it includes /sbin and /usr/sbin. iwconfig is not found because it's not on PATH. But you can invoke it with full path specified: /sbin/iwconfig. But sudo -s is different from su, see below.

OTOH, when you gain root privileges via su - or sudo -i it's the same as if you were logging in as root: all startup scripts for root are executed and /sbin and /usr/sbin get included on PATH.

When you execute a single command via sudo, a minimal environment is set anew by sudo. This includes PATH.

And here is where the difference between su and sudo -s comes into play. sudo -s uses settings in /etc/sudoers just like sudo command does. Because /etc/sudoers on Debian sets PATH (see secure_path in /etc/sudoers), iwconfig gets found even though the startup scripts for root weren't executed.

michaelk · 06-05-2020, 03:15 PM

Quote:

When you issue a command without path it's searched in the current directory, then in directories pointed to by environment variable PATH.

That is true for Windows but not linux. That is why you need the ./ (or use absolute path) if you want to run a program that is not located in a directory in your path environment.

shruggy is correct in regards that environment does not matter if using the absolute path to run the command i.e /sbin/iwconfig.

shruggy · 06-05-2020, 03:35 PM

@michaelk. Thanks for correcting me. You're right of course.

Trent29 · 06-05-2020, 04:22 PM

Wow, thanks for the quick and extraordinarily detailed explanations.

Much appreciated and makes sense.