Changing to root user inside shell script

Question

I have a shell script which needs non-root user account to run certain commands and then change the user to root to run the rest of the script. I am using SUSE11. I have used expect to automate the password prompt. But when I use spawn su - and the command gets executed, the prompt comes back with root and the rest of the script does not execute.

Eg.

< non-root commands>
 spawn su -
<root commands>

But after su - the prompt returns back with user as root. How to execute the remaining of the script.

The sudo -S option does not help as it does not run sudo -S ifconfig command which I need to find the IP address of the machine.

I have already gone through these links but could not find a solution: Change script directory to user's homedir in a shell script

Changing unix user in a shell script

Answer 1

sudo will work here but you need to change you script a little bit:

$ cat 1.sh 
id 
sudo -s <<EOF
echo Now i am root
id
echo "yes!"
EOF

$ bash 1.sh
uid=1000(igor) gid=1000(igor) groups=1000(igor),29(audio),44(video),124(fuse)
Now i am root
uid=0(root) gid=0(root) groups=0(root)
yes!

You need to run your command in <<EOF block and give the block to sudo.

If you want, you can use su, of course. But you need to run it using expect/pexpect that will enter password for you.

But even case you could manage to enter the password automatically (or switch it off) this construction would not work:

user-command
su 
root-command

In this case root-command will be executed with user, not with root privileges, because it will be executed after su will be finished (su opens a new shell, not changes uid of the current shell). You can use the same trick here of course:

su -c 'sh -s' <<EOF
# list of root commands
EOF

But now you have the same as with sudo.

Answer 2

There is an easy way to do it without a second script. Just put this at the start of your file:

if [ "$(whoami)" != "root" ]
then
    sudo su -s "$0"
    exit
fi

Then it will automatically run itself as root. Of course, this assumes that you can sudo su without having to provide a password - but that's out of scope of this answer; see one of the other questions about using sudo in shell scripts for how to do that.

Answer 3

The easiest way to do that would be to create a least two scripts.

The first one should call the second one with root privileges. So every command you execute in the second script would be executed as root.

For example:

runasroot.sh

sudo su-c'./scriptname.sh'

scriptname.sh

apt-get install mysql-server-5.5

or whatever you need.

Answer 4

Short version: create a block to enclose all commands to be run as root.

For example, I created a script to run a command from a root subdirectory, the segment goes like this:

sudo su - <<EOF
cd rootSubFolder/subfolder
./commandtoRun
EOF