I have a linux user (user2) which has set as shell /usr/sbin/nologin (to block logins). No when I try to switch to this user with sudo su user2 I get the info that this account is not available. But whe I user sudo -su user it works fine.
What is now the difference between su and -su. Or what does -su. I tried to get the help with -h or --help or the manpage but I coulnd not find anything helpfull.
sudo -su user is short for sudo -s -u user. The -s option means to run the shell specified in the environment variable SHELL if this has been set, or else the user's login shell. The -u user option means to run the command as the specified user rather than root. These options are documented under man sudo.
sudo su user will use sudo to run the command su user as the root user. The su command will then invoke the login shell of the specified username. The su user command could be run without the use of sudo, but by running it as root it will not require the password of the target user. For more information see man su.
So the two commands look similar (largely coincidentally) and have a somewhat similar effect when the target user has the same login shell as that of the invoking user. However, in the case that the SHELL environment variable is set in the invoking user's environment (which it usually is, and it is typically /bin/bash), and that the target user has a login shell which differs from this (such as /usr/sbin/nologin), there is then a difference between which shell gets executed by these two commands, and this is what you are seeing.
A - is very common for passing paramters. In your case -su is there to pass user. A very common way to get these command line arguments. Is this piece of code in C: int main(int argc, char *argv[])
sudo su means you get root privileges in your terminal. And sudo su user2 means you're trying to execute user2 after getting root privileges (You'll get an error in the most cases).
