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Is it possible to create a temporary empty environment for a new user in a Shell like Bash or zsh?

I mean like the incognito mode in Chrome which opens an isolated environment in which everything you did gets removed locally (no history, no cookies, no cache, etc). Is such a thing possible in a Linux Shell?

To just add the obvious (at this point it hasn’t been mentioned), this is one of the intentions of jails/containers/zones, and although it may seem like overkill to the uninitiated (I’m assuming nothing), it’s trivial if one is already using them. (And if one is not using them, attempting to reinvent this wheel will be terribly error-prone.)

In short, create a temp docker instance, do your worst, then remove it afterwards. https://docs.docker.com/get-started/

See also this backgrounder: https://blog.jessfraz.com/post/containers-zones-jails-vms/

You can use this if you just want to run the program without your configuration files, but you trust that the program is not malicious and not to try to look outside the box.

I wrote a little something a while back that sets up a temporary directory and starts a shell with a minimal environment. I use this many times daily to test my solutions to questions for this site.

https://github.com/kusalananda/shell-toolbox

FreeBSD users can also use the devel/shell-toolbox port.

The command is called shell and creates a temporary disposable working directory, optionally pre-populated with the contents of another directory, and starts a shell in it. When the shell session exits, the temporary directory is disposed of (depending on command line flags used).

This can also be used to start another shell other than the user's login shell.

It doesn't create a temporary user (as this would require administrative permissions), but it does set the HOME variable to the temporary directory, which means that any references to $HOME or ~ would resolve to the temporary directory and not to the "real home" of the user. It is not a "safe" environment in the sense that the rest of the system is protected, but it provides an interactive shell in a throw-away directory where created files and directories will be cleaned up when finished with minimal impact from your ordinary shell environment.

Example:

[box] $ shell -s "$HOME/skel" zsh
shell: info: Copying /home/kk/skel into /tmp_mfs/shell-zsh.5IAh9F2B
shell: info: Starting /usr/local/bin/zsh in /tmp_mfs/shell-zsh.5IAh9F2B
$ ls -a
. .Xdefaults .cvsrc .mailrc .vimrc
.. .cshrc .login .profile .zshrc
$ echo "$HOME"
/tmp_mfs/shell-zsh.zqHtjz49
$ env
HOME=/tmp_mfs/shell-zsh.zqHtjz49
PATH=/usr/bin:/bin:/usr/sbin:/sbin:/usr/X11R6/bin:/usr/local/bin
PS1=$
SHELL=/usr/local/bin/zsh
TERM=screen
LOGNAME=kk
SHLVL=1
PWD=/tmp_mfs/shell-zsh.zqHtjz49
OLDPWD=/tmp_mfs/shell-zsh.zqHtjz49
_=/usr/bin/env
$ exit
shell: info: Removing /tmp_mfs/shell-zsh.5IAh9F2B

It doesn't do chroot or anything fancy like that. It's basically a glorified wrapper around env -i.

See the shell documentation.

Use a snapshot in a virtual machine.

1. Create a virtual machine with the needed prerequisites.


2. Create a snapshot of the VM.


3. Do any test in your VM.


4. Restore the snapshot, deleting any modification you did to the system.


5. Go to 3.

If all you want a totally clean shell void of all environment variables or aliases, you can spawn a new shell then type:

$ unalias -a
$ unset `set|grep '^[A-Z_a-z].*=' |sed 's|=.*$||g'`

This will pretty much remove everything that can be removed. Of course you'll want to set PS1 to something otherwise you won't be able to tell if you're in a quote or at the command prompt.

Note: This only applies to bash and zsh.