Just the other day we were having a discussion on using the root shell in Ubuntu. Now, remember, the root user account is disabled with no assigned password on a default Ubuntu system so administrative tasks need to be done using the sudo command. For nearly all of the administration you would need sudo will be adequate. There are occasionally those fringe cases where you might require a root shell. Below I have a few alternatives and then, if you must, the correct way of opening a root shell.
For more information please see the RootSudo page on the Ubuntu Community Wiki.
Alternatives To A Root Shell
One of the most common reasons that a user might need a root shell is due to output redirection not working as expecting while using sudo. This can be bypassed fairly easily. Let me outline an example:
sudo echo “foo” > /root/somefile
The above example will not work because the normal user does not have access to write to the root user home directory, and combining the redirection in the command we’ve lost sudo access.
An alternative that will work would look something like this:
echo "foo" | sudo tee /root/somefile
This will echo the output on the console but the tee command ('man tee‘ for more information) will also take that output and write it to the file as expected. Also note that 'tee -a' will work in the same fashion as >>, appending the data to the current file vs overwriting.
The Proper Way To A Root Shell
If you still need a root shell (perhaps you’ve come across a different scenario? perhaps you’re just lazy? perhaps you’re coming from another distribution?) let me outline the proper way to gain a root shell.
DISCLAIMER: This should be avoided if at all possible. It is not suggested to run a root shell on an Ubuntu system. Use at your own risk. See examples above, etc.
sudo -i
The command sudo -i is the equivalent to the 'su -' command. This will properly change to the root user, switch to the root user’s home directory, use his (her?) environment values, etc.
sudo -s
The command sudo -s is the equivalent to the 'su' command. This will change to the root user but will not properly use his (her?) environment values, etc.
The WRONG Way To A Root Shell
Please DO NOT use the following methods to gain root access:
sudo bash, sudo sh, sudo su -, sudo su, sudo -i -u root
If you currently do use these methods this post was written for you!
UPDATE: Based on the feedback in the comments for this post I’ll try to expand the reasoning on *why* the right way is the preferred way.
First of all we need to understand some background information. When a user creates a session there are a number of environment values that are set. To have a look at some of these try this command:
env
This will output a number of details about the current working environment. These environment values may be different for different users. Some of the values are generated by way of the .bashrc file (assuming a bash shell, of course), the .bash_profile, etc. Take a look at the .bashrc in your users home directory and compare it with the .bashrc in root’s home directory.
diff -u ~/.bashrc /root/.bashrc
You should see some differences, and this is just from one of the multiple files that are read during a proper login.
When creating a root shell by using ‘sudo bash‘ you are not incorporating the root environment properly. You are creating a shell with root privileges but the env output is still that of your user. Each user, whether unprivileged or root, should have unique environment settings to truly be that user. This will be the case for ‘sudo bash‘, ‘sudo su‘ and ‘sudo sh‘.
