Problem with running a script at startup as root?

Question

The main question:

Is there a way I can run 'completely' one of my script when ubuntu's desktop appears no matter if root , administrator, desktop user or an unprivileged user logged in?

What does the script do?

The script mounts a partition, looks for a file in that partition and finally on the basis of that file a decision of copying a partition to another partition is made. That copying is done via

dd if=/dev/sda2 of=/dev/sda5

When does the script run finely?

Script runs smoothly when I run it from the terminal by

sudo ./my_copying_script

This command asks me for the password of currently logged in user. I enter the password and the script starts working.

When does the script NOT run finely?

I want to run the script at startup. I set it a startup program by using the Startup Applications utility of Ubuntu. Script ran at startup but exited at the dd command returing following error:

dd: opening '/dev/sda2': Permission denied 

On edk's suggestion I set the owner of my_copying_script as root and set the SUID. Now the permissions of my_copying_script are (-rwsr-sr-x). edk's point of view was that once I set the suid, the startup program will run with the permissions of its owner. I did that but the same /dev/sda2 permission denied error came up.

I then prefixed the dd with sudo as mentioned below

 sudo dd if=/dev/sda2 of=/dev/sda5

but this returned following error:

sudo: no tty present and no askpass program specified

Answer 1

Usman, I think you have at least two options I already mentioned.

An easiest way

Make a set-UID binary that will(check who started it & allow usage if parent process owner can run it) run prepared script and exit. Put into startup in your desktop manager, that's all. Just be warned it is not the best way and it needs a bit of C coding. Basically you need to make a code like this sample:

int main(){
    setuid(0);
    system("/bin/sh /root/bin/mounts.sh");
}

Be aware that this is a hack, not solution, really. And be sure to use root:allowed_group and 4750 rights on binary if you don't need it to be run by everyone. Remember to add all users which may start this up to allowed_group(pick your name).

A good way

Other, much better way is to make a sort of daemon, spawned @ system boot(say, from init-scripts), but I am unsure how exactly are you going to detect when new X session is started, I wasn't into that topic yet, I can't give any clear advices here.

Answer 2

Set correct permissions on mounted drive path then and you're done.

Answer 3

sudo will only run a program as a different user if one of these 3 conditions has been met (as far as passwords are concerned):

1. the NOPASSWD option is specified
2. the user entered the correct target password
3. the user entered the correct source password

Since options 2 and 3 require a TTY (sudo won't read from a pipe) it won't run if it can't find one. Check your script if at any point you're running a script remotely using ssh, as it's possible that it won't allocate a TTY for a non-interactive remote command.

Quoted from: Here

Answer 4

Add the entry to /etc/fstab, use chown and chmod to modify permissions to only give root access to the mounted partition.

sudo chown -R root:root /mnt
sudo chmod -R 770 /mnt

Answer 5

A possible solution will be to add your user and the command he is trying to invoke to /etc/sudoers with NOPASSWD parameter. Cut from /etc/sudoers:

# Uncomment to allow members of group sudo to not need a password
# (Note that later entries override this, so you might need to move
# it further down)
# %sudo ALL=NOPASSWD: ALL

So maybe you will need something like:

myuser ALL=NOPASSWD: mount

I'm not very sure about the exact syntaxis, you'd better google for it.

EDIT: If you are trying to mount a network drive, adding a record to /etc/fstab probably will not work, because network services are not loaded at time fstab is executed.