I know what should be the difference between su and su -, but in my system (Debian) for example PATH is the same:
[root]# su [root]# echo $PATH /user_path/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin [root]# exit [root]$ su - [root@debian ~]# echo $PATH /user_path/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin So I'm starting to think that the settings can be changed in configuration files.
For configuring the su PATH, have a look at /etc/login.defs:
ENV_SUPATH PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin ENV_PATH PATH=/usr/local/bin:/usr/bin:/bin:/usr/local/games:/usr/games There are also a number of other places PATH can be changed, including:
/etc/environment/etc/bash.bashrc/etc/profile/etc/profile.d/*~/.bashrc~/.bash_profileWithout anything special in per-user settings, su seems to be getting its PATH from /etc/environment and su - seems to be getting its environment from /etc/login.defs ENV_SUPATH.
So on your system, my guess is that you have the same PATH value in /etc/login.defs as in /etc/environment, or you have some extra configuration in /etc/profile.d, /etc/bash.bashrc, or some rc file in /home/someuser.
Parameter - means starting environment which is almost the same as with login environment for that user.
Without - environment is same as original user's environment.
For example PATH is usually same for root and normal users. In some systems there is no sbin folders for normal users. You can't disable - from su easily. Of course you can go to edit the source code.
You can try this by running
export FOO=bar su # enter your password echo $FOO logout su - # enter your password again echo $FOO In first time echo $FOO prints "bar" and in second time it's empty.
suprogram since this question was written and answered. unix.stackexchange.com/q/460478/5132