Linux run application as user

How to run an Application as another user?

I use krusader for file management stuff. the problem is that apache’s DocumentRoot should be under chown www-data:www-data /path/to/www . so using krusader (which is run under my account) I’ve not write access to /path/to/www while I really need. I don’t know how other developers can continue doing things with such a restriction! I wondered if I could run krusader as www-data then I will be able to easily play with files. but using su — www-data asked me for www-data ‘s password!! So, how can I run an application (like krusader) as another user (like www-data) in Gnome? or is there any other solution for my case? (tough I’m really curious to know the answer!) keep in mind that I know I can run it as root! but this will cause some permission problems when using cp and mkdir , you know. PS: sudo and gksudo did not help:

$ gksudo -u -www-data krusader No protocol specified krusader: cannot connect to X server :0.0 

Final Note: according the best answer, i did chmod u+w /path/to/www and my problem solved. but i still has not been succeeded in opening krusader as another user!

9 Answers 9

xhost +SI:localuser:uname gksudo -u uname -l "firefox" xhost -SI:localuser:uname 

Where uname = the name of impersonated user. Seen there: http://ubuntuforums.org/showthread.php?p=10399617

Works on my maverick box, there’s no sound in the forked skype and ~/.profile.d is not executed as it might.

If you’re running this from the menu system you’ll want to use alacarte (System > Preferences > Main Menu) and change the entry for krusader and add in front of it: gksudo -u www-data which should produce something like:

gksudo -u www-data krusader

This will launch the administrative task prompt window which, according to the GKSudo Manpage, is a

GTK+ Frontend for su and sudo

Using just gksudo without the -u switch will run the command as root.

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Background

I’m trying to restart some programs ( mail-notification and stalonetray ) regularly, as they appear to die frequently. I want to set restart them whenever NetworkManager reconnects. Hence, I have them triggered by a script in /etc/NetworkManager/dispatcher.d/ .

Scripting

#!/bin/bash sudo -u foo_user pkill mail-notificati -x sudo -u foo_user DISPLAY=:0 mail-notification & 

This works fine if I run it directly as a user. However, if I call it from root’s script, it fails. I am prompted to enter the passwords for mail-notification ; it cannot read Gnome Keyring. How can I run this program as foo_user in every way?

What does «in every way» mean? Every program that a user runs can have different environment, so saying that (for example) DISPLAY should be set for it to be «in every way» doesn’t make much sense. You’d need to define this question more for it to make sense.

@ChrisDown I mean I want it to work when running the script as root as it does when running the script as foo_user . I appreciate that DISPLAY isn’t necessarily relevant here, but included it as an example of what I was doing.

That still doesn’t clarify, because «doing the same thing when run as root as when run as a user» doesn’t make sense — an environment is per-process, not per-user.

@ChrisDown Sorry, I’m afraid I don’t understand the distinction in this case. Here, I’m asking to run the mail-notification process as in foo_user ‘s environment.

How do you know foo_user is logged in, and on which display? On a single-user system it’s perhaps reasonable to assume that it’s always :0.0 but it is not reasonable to assume that the user is logged in at all times. Anyway, this makes more sense to run within the X session script of foo_user , which will remove both your original problem and the complications it caused you to want to try to solve.

4 Answers 4

In 2021

In short:

To run a command as another user you can use this commands:

runuser -u user — command
can be used only by root to run commands as another user.
do not require authentication.
do not create log messages.
has permission limitations and issues.

su — user -c command
can be used by any user.
require authentication as target user.
create message in /var/log/auth.log or /var/log/secure .

sudo -u user command
can be used by the user with root privileges or the user from the sudoers file.
require authentication as current user (you).
create message in /var/log/auth.log or /var/log/secure .

pkexec —user user command
can be used by any user.
require authentication as target user.
create message in /var/log/auth.log or /var/log/secure .
replacement for GUI tools such as gksu or gksudo .

More info:

Run a GUI application as another user:

If you want to run a GUI application as another user, you need first allow to the target user connecting to your display:
xhost +si:localuser:user
then use runuser / su / sudo / pkexec to run the application,
and then use xhost to prevent the subsequent connections:
xhost -si:localuser:user

Excellent answer! I tried to use this to run spotify as a non-privileged system user. Your answers, especially for running a GUI app, worked for me. However, I did neet to pass in my DISPLAY var through sudo using the -E flag. Also, I was ignorant and didn’t realize localuser is that literal string. Finally, a gui app may fail to various other issues with expecting a normal user’s profile. HTH

Regarding GUI: Is this safe though? Can user send arbitrary input after having been given access to the display?

You can always use good old su :

This command opens a sub-shell as the user you want to impersonate. As root you can use it without being prompted for a password.

su foo_user -c whatevercommandyouwant

I’m not sure what -x is (I get su: invalid option — ‘x’ ), but after removing that, it still fails as per the question.

Hi, sorry for the confusion, but my aim is not to provide a one shot solution but to tell you how the command su works. If you did a direct cut and paste you may have got an error. But, that’s exactly why I added a link to the su man page as the first thing. Please cut and paste this into the shell and see what it says 😉

Sorry, I still don’t understand. Are you suggesting that su will provide a different env to sudo that should fix my problem? If so, then that doesn’t seem to be the case.

Yes. Again: man7.org/linux/man-pages/man1/su.1.html » su allows to run commands with a substitute user and group ID. When called without arguments, su defaults to running an interactive shell as root. For backward compatibility, su defaults to not change the current directory and to only set the environment variables HOME and SHELL (plus USER and LOGNAME if the target user is not root). » anyway sudo has nothing to do with that, sudo su does. sudo grants permissions to run commands that require specific privileges to your user.

If you want to interact with a GUI from a process that isn’t started from that GUI, you need to set a few environment variables: at least DISPLAY , possibly also XAUTHORITY if it isn’t in the default location, and for many modern programs you need to set DBUS_SESSION_BUS_ADDRESS .

But a more reliable approach for your problem would be to not restart those programs from NetworkManager. In addition to the difficulty of successfully launching them, you also need to worry about whether you’re logged in at all, and if there might be other users and other displays to consider, and so on. Instead, kill those programs, but don’t restart them. In your normal session, instead of starting them directly, start them from a supervisor that restarts them if they die. I think systemd includes this functionality (but I don’t know how to use it); or you can use dedicated supervisor programs such as monit, supervise, …

Read, copy and install run-as , a Bash and a Python script which wrap up usage of machinectl , xhost and of managing running dbus and setting variables to run a graphical application for you:

To run a graphical application do

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Run a shell script as another user that has no password

I would like to run a script from the main ubuntu shell as a different user that has no password. I have full sudo privileges, so I tried this:

sudo su -c "Your command right here" -s /bin/sh otheruser 

Then I have to enter my password, but I am not sure if that script is now really running under that user. How can I confirm that the script is really running under that user now?

10 Answers 10

You can do that with su or sudo , no need for both.

sudo -H -u otheruser bash -c 'echo "I am $USER, with uid $UID"' 

The relevant parts of man sudo :

-H The -H (HOME) option requests that the security policy set the HOME environment variable to the home directory of the target user (root by default) as specified by the password database. Depending on the policy, this may be the default behavior. 

(Starting from Ubuntu 19.10, -H is no longer needed as this is now the default behaviour. See: How does sudo handle $HOME differently since 19.10?)

-u user The -u (user) option causes sudo to run the specified command as a user other than root. To specify a uid instead of a user name, use #uid. When running commands as a uid, many shells require that the '#' be escaped with a backslash ('\'). Security policies may restrict uids to those listed in the password database. The sudoers policy allows uids that are not in the password database as long as the targetpw option is not set. Other security policies may not support this. 

su can only switch user without providing a password if you are root. See Caleb’s answer

You can modify the /etc/pam.d/su file to allow su without password. See this answer.

If you modified your auth file to the following, any user that was part of group somegroup could su to otheruser without a password.

auth sufficient pam_rootok.so auth [success=ignore default=1] pam_succeed_if.so user = otheruser auth sufficient pam_succeed_if.so use_uid user ingroup somegroup 

rubo77@local$ su otheruser -c 'echo "hello from $USER"' hello from otheruser 

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