CODEWITHSUNDEEP
javalinuxsudo
evaleaf
evaleaf

Reputation: 33

How to discover linux username with administrator privileges in Java

I created a program which needs administrator privileges to be executed (in this program I am using a port which is <1024).
So I use this command to execute:

sudo java -jar example.jar

In my program I try to create a folder in this path:

Paths.get("/home/" + System.getProperty("user.name"))

The problem is that System.getProperty("user.name") answers with "root" and so my new directory is in "/home/root/", but I want it in "/home/my_username".
My question is: how can I discover my username and then create the new folder in the right path?

Upvotes: 3

Views: 797

Answers (3)

Luis Colorado
Luis Colorado

Reputation: 12635

Linux user name is normally bound to the USER environment variable at login(1) time. The best approach is to use this variable, as other means (running who(1) or id(1) command for example) all do inspect it (using the uid as parameter, to scan files for it). The same applies for HOME and SHELL variables. All of these are collected by login(1) on authenticating the user (or by the PAM libraries) and get propagated to all derived processes through the environment.

The weird fact is that you can have several usernames bound to the same uid, and not using the environment can lead you to getting the wrong answer (if you scan the /etc/passwd file with your uid as argument, you can get to a different passwd(5) file entry ---of course, with the same did) Use:

String username = System.getEnv("USER");

for it.

On other side, if you have created a new session (with sudo(1) command or similar) and switched both uid and euid and the environment has been changed (reinitialised), how you distinguish this from a proper login made by root account. In that case there are no traces that the process were invoked by a non-root user.

Upvotes: 0

Peter Lawrey
Peter Lawrey

Reputation: 533432

If you do

sudo whoami

it responds with

root

however if I do

sudo bash -c 'echo $SUDO_USER'

I get

peter

You do this from Java with

String user = System.getenv("SUDO_USER");
if (user == null)
    user = System.getProperty("user.name");

Upvotes: 2

Elliott Frisch
Elliott Frisch

Reputation: 201399

You can change from

Paths.get("/home/" + System.getProperty("user.name"))

to the user.home System Property like

Paths.get(System.getProperty("user.home"))

Upvotes: 3

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