Why is sudo bash needed?

You would be much better off doing: $ sudo sh -c 'cd /home; ./gitpull.sh' Because the commands invoked as root will be logged. Invoking a shell directly through sudo avoids all of the security benefits of sudo and should be avoided.

sudo allows users to run programs with the security privileges of another user (normally the superuser, or root). bash starts a new bash shell. So, sudo bash starts a new bash shell with the security privilege of root user.

sudo <shell>, if it works, betrays a poor installation of sudo and a potential security weakness. sudo should not be configured to allow arbitrary commands like shell; the purpose of sudo is to allow authenticated non-root users to run certain commands as root, without knowing the root password. If sudo bash is allowed to any user, that user is root simply by virtue of knowing his own password. If an attacker obtains the password of any one of the accounts which are able to do sudo bash, the attacker thereby has root. The proper way to do the equivalent of sudo bash (obtain a root shell) is su, followed by giving the root password, not your own.