su is a utility to run a shell or other command as another user (root by default).

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86
votes
7answers
12k views

Which is the safest way to get root privileges: sudo, su or login?

I would like to have the root account in safety even if my unprivileged user is compromised. On Ubuntu you can only use sudo for "security reasons" by default. However I am not sure it is any safer ...
81
votes
6answers
25k views

Where did the “wheel” group get its name?

The wheel group on *nix computers typically refers to the group with some sort of root-like access. I've heard that on some *nixes it's the group of users with the right to run su, but on Linux that ...
75
votes
2answers
11k views

Why do we use su - and not just su?

I don't understand why su - is preferred over su to login as root.
28
votes
6answers
18k views

What is the need for `fakeroot` command in linux

Why do we need fakeroot command at all? Can't we simply use the sudo or su commands? The man page says: fakeroot - run a command in an environment faking root privileges for file manipulation ...
17
votes
2answers
9k views

su vs sudo -s vs sudo bash

What is the difference between the following commands: su sudo -s sudo bash I know for su I need to know the root password, and for sudo I have to be in the sudoers file, but once executed what is ...
14
votes
1answer
1k views

What's the difference between sudo su - and sudo su --

When I am working on our RHEL machines, I use sudo su - to switch to being root. One day, a typo meant I typed sudo su -- instead - it seems to me that everything was the same as with a single hyphen, ...
13
votes
4answers
865 views

What is SSH - the protocol and what is ssh - the utility?

What is SSH - the protocol? What is ssh - the unix utility and how does it work? How is SSH protocol related to SFTP? What is sshd? Does the command su use ssh or sshd?
12
votes
4answers
11k views

Why doesn't “sudo su” in a shell script run the rest of the script as root?

A sample script can be as below: #!/bin/bash sudo su ls /root When using ./test.sh as the normal user, instead run ls as super user and exit, it switches to root; and when I logout, it executes ls ...
12
votes
2answers
12k views

I Can't login as root with su command, but I can with SSH

How is it possible that I cannot log in as root by su root or su (I get incorrect password error), but I can log in by ssh root@localhost or ssh root@my_local_IP with the same password? I'm using ...
11
votes
2answers
9k views

What is the difference between 'su -' and 'su root'? [duplicate]

Possible Duplicate: Why do we use su - and not just su? I understand that root doesn't have to be a superuser. But in the case that it is ... what is the difference between sudo su - and ...
10
votes
3answers
7k views

.bash_profile not sourced when running su

I have a user, say user1, which has modifications to its .bash_profile, one of them changing the PATH, e.g.: export PATH=/some/place:$PATH. This change works fine if I log on as user1 or do a su - ...
9
votes
2answers
3k views

When do su and sudo use different passwords?

I am able to run anything using sudo; my password is accepted. But whenever I try to do su from a shell, it fails with: su: incorrect password What can the problem be?
9
votes
4answers
3k views

su does not change user but does not respond with an error either

While logged in as root I would like to su to a specific regular user. I run su username and immediately receive the prompt back, still as root. There is no error given. I'm aware of the old "the user ...
9
votes
1answer
801 views

Why does “su -c <command> &” seemingly allow a command to run in the background without hanging up

I was helping a colleague who was having problems with a background process intermittently dying. I found out that they were starting the background process by logging in to the server and executing: ...
8
votes
2answers
222 views

How do I elevate privileges in the middle of pipeline?

My guess was as follows: echo "Generating some text" | su - -c cat >/output/file But su says: su: must be run from a terminal What would you do?
8
votes
1answer
1k views

What is the difference between 'sudo' and 'su -c'

Is there any difference between using sudo and using su -c? There are situations where one should be used but not the other? I was previously using Ubuntu where sudo appears to be ubiquitous but now ...
7
votes
4answers
2k views

sudo permission denied but su grants permission

this is the first occurrence where su was required for me. I read an article about changing the value in /sys/devices/virtual/backlight/acpi_video0/brightness to alter my laptop's screen brightness. ...
7
votes
5answers
5k views

How do I suppress dd output?

I have a bash script that creates some file using dd. The problem is dd throws a great amount of output that is going to mess with the output of my script. Searching around I've found a solution: dd ...
7
votes
2answers
8k views

“su” with error “X11 connection rejected because of wrong authentication.”

As root, I'm connecting to a remote host to execute a command. Only "standarduser" has the appropriate id-file and correct .ssh/config, so I'm switching the user first: su standarduser -c 'ssh -x ...
7
votes
1answer
1k views

How to stop users from Switching to Root user

I have disabled the root user login from Sshd.conf file so now no one can login using root user even if they know the password SOMEHOW. Now I have 3 users in server ROOT,EMERG and ORACLE. I want to ...
7
votes
3answers
2k views

Difference between sudo -i and sudo su [duplicate]

I was wondering what the difference is between sudo -i and sudo su?
7
votes
1answer
6k views

How to run a GUI program as a different user (Debian)?

Using a terminal, I can change the running user with su and sudo — but how can I do that by clicking on an icon/shortcut on the desktop/start menu? If I have to be root to execute I will be asked ...
6
votes
4answers
2k views

Why can't we execute a list of commands as different user without sudo?

This question has been asked in a different way in other forums. But there has not been a decent explanation why you can't do the below in bash. #!/bin/bash command1 SWITCH_USER_TO rag command2 ...
6
votes
2answers
10k views

Is it possible to su without being prompted for a password?

I suspect su doesn't have any way to allow passing the password from the shell instead of being prompted for one, for security reasons (couldn't find anything in the MAN). Is this true?
6
votes
2answers
265 views

Why doesn't su change the user ID of the shell from which it was run?

Instead, it starts a new shell process with the new user ID. The original shell is blocked until the new shell completes and su exits. Why does it work like this?
5
votes
3answers
2k views

Why is the 'sudo' password different than the 'su root' password

On my personal machine, I often type sudo in front of certain commands in order to accomplish administrative tasks. I had hoped to avoid doing this throughout the day, by typing su root and providing ...
5
votes
2answers
53 views

Permissions depending on how you login: ssh/su/sudo

As user I have access to a remote linux machine where I can: sudo su - other_user Among other things, this allows me to add my own public key to authorized_keys for other_user, which effectively ...
5
votes
3answers
2k views

Changing the UID of files in /proc

In a follow up to this question about changing the UID of a user, it is recommended to change the ownership of all files on the system (this answer) find / -uid 1000 -exec chown 5000 '{}' \+ where ...
5
votes
1answer
666 views

What does su - `whoami` command do?

I am running a script in my project and I see this command su - `whoami` I am having a few basic questions: What does this command do ? What is the significance of `` quotes outside the whoami ...
5
votes
1answer
166 views

How to allow to run su instantly after I added the user to the appropriate group

I have the su executable with the following permissions: bash-4.2# ls -la /bin/su -rws--s--- 1 root wheel 59930 Sep 14 2012 ./su When I am logged in as a user, not in the wheel group and try to ...
5
votes
2answers
1k views

how to ssh -Y and then su - <another user> and still forward X applications to your local machine

it is easy enough to 'fetch' (ie draw locally) a remotely running linux application: If I ssh -Y to the remote machine and run an application, that application will surely enough pop up in my local ...
5
votes
2answers
1k views

Alternative to su/sudo on barebone system

I'd like to run some unit tests in a barebone chroot jail on Solaris. There's no su or sudo, and a copy of su (with libpam.so.1) just returns exit code 1 without any output, with or without ...
5
votes
1answer
152 views

Getting the process-id out of command launched with “su -c”

I am running a java program inside a shell and writing the process-id to a text file. So when I do this: nohup java app.Main > /dev/null 2>&1 & echo $! > /var/run/app.pid It works. ...
4
votes
1answer
516 views

Why do I need to use newgrp or su (or logout and login again) to have new group memberships applied?

What is it that makes new group membership require a new login (or new login shell as started by su or newgrp) to be visible? Just running another bash (or whatever other shell) instance with --login ...
4
votes
2answers
292 views

How do I execute a command on login for a system user with no home folder and no personal .bashrc file?

I set these users' home folders through the /etc/passwd file, but when they log in I would like them to activate a python virtualenv. If they had a personal .bashrc file, I'd just include the activate ...
4
votes
4answers
3k views

Should I use `sudo` or `su` in a startup script?

I have a personal program, that has a server/client design. The server daemon part of it, should be run as its own limited user, and the program was not designed to drop its root privileges (if ...
4
votes
2answers
16k views

su options - running command as another user

I was wondering how to run a command as another user from a script. I have the script's owner set as root. I also have the following command being run within the script to run the command as the ...
4
votes
2answers
54 views

Use non-root user configuration for root account

When I work with the terminal and use su or sudo to execute a command with the root user's permissions, is it possible to apply the configuration of my "non-root user" (from which I am invoking su or ...
4
votes
1answer
160 views

Is there any point in using `sudo` when you are the sole user of your machine?

I'd like to know if there is any reason why I should use sudo instead of su, taking into account that I am the owner and sole user of my machine (and hence have root access whenever I want). Also, in ...
4
votes
2answers
403 views

Two GUI applications as different users on the same screen

I am logged as user A. I want to run a GUI application as user B. User, not root. User B is local too, not remote, I only need different environment variables. I don't want to run the second X, I want ...
4
votes
3answers
2k views

Find out if a session is running under `su`

I'm trying to check whether the current shell session is running within a su login session. What's the best way to test this condition?
4
votes
2answers
3k views

Change user and load entire environment in shell script

I'm having some trouble with an upstart script of ours that changes user and starts up a few ruby daemon processes. In the past i would simply bash -c "do the business" -l someuser making sure to use ...
4
votes
3answers
2k views

Automate login with sudo and su

I know the security risks, but I am performing this experiment/exercise on an old, seldom used *nix machine I have laying around the house. So doing this exercise will not bring any security risk to ...
4
votes
1answer
2k views

Command : must be run from a terminal

I have a shared hosting account, I logged using ssh. when I type for example su I had this output : su: must be run from a terminal Is this error relative to the fact that I don't have sufficient ...
4
votes
3answers
969 views

`$XAUTHORITY` appears from 'nowhere' on su+tmux

When I switched from su+bash to su+tmux+zsh I noticed that I get $XAUTHORITY variable defined as /root/.xauthXXXXXX where XXXXXX are 6 random alphanumeric characters. With previous configuration X ...
3
votes
2answers
601 views

Sudo Su automated login

I want to automate the login process with sudo su. I have seen lot of questions on these, but none of them are working for me. Automate login with sudo and su Here's my what I tried so far echo ...
3
votes
2answers
3k views

su vs su - (on Debian): why is PATH the same?

I know what should be the difference between su and su -, but in my system (debian testing) for example PATH is the same: [root]# su [root]# echo $PATH ...
3
votes
2answers
160 views

Is there a graphical sudo (kdesudo, gksudo, su-to-root, …) tool that works passwordless?

Apparently gksudo is not obeying /etc/sudoers, neither does kdesu. Therefore asking the other way around... Is there any su-to-root, gksudo, kdesudo, etc. alike tool, that supports starting gui ...
3
votes
2answers
5k views

su - user doesn't work for users without a password

I've created a user on CentOS with useradd -M username. Now, I want to become that user just like su - username. It asks me for a password for that user but I didn't set a password for that user. As ...
3
votes
2answers
520 views

Passing arguments to su-provided shell

man su says: You can use the -- argument to separate su options from the arguments supplied to the shell. man bash says: -- A -- signals the end of options and disables further option ...