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The su
(short for substitute or switch user) utility allows you to run commands with another user’s privileges, by default the root user.
Using su
is the simplest way to switch to the administrative account in the current login session. This is especially handy when the root user is not allowed to log in to the system through ssh
or using the GUI display manager.
In this tutorial, we will explain how to use the su
command.
How to Use the su
Command #
The general syntax for the su
command is as follows:
su [OPTIONS] [USER [ARGUMENT...]]
When invoked without any option, the default behavior of su
is to run an interactive shell as root:
su
You will be prompted to enter the root password, and if authenticated, the user running the command temporarily becomes root.
The session shell (SHELL
) and home (HOME
) environment variables
are set from substitute user’s /etc/passwd
entry, and the current directory is not changed.
To confirm that the user is changed, use the whoami
command:
whoami
The command will print the name of the user running the current shell session:
root
The most commonly used option when invoking su
is -
(-l
, --login
). This makes the shell a login shell with an environment very similar to a real login and changes the current directory
:
su -
If you want to run another shell instead of the one defined in the passwd
file, use the -s
, --shell
option. For example, to switch to root and to run the zsh
shell, you would type:
su -s /usr/bin/zsh
To preserve the entire environment (HOME
, SHELL
, USER
, and LOGNAME
) of the calling user, invoke the command with the -p
, --preserve-environment
option.
su -p
When the -
option is used, -p
is ignored.
If you want to run a command as the substitute user without starting an interactive shell, use the -c
, --command
option. For example, to invoke the ps
command as root, you would type:
To switch to another user account, pass the user name as an argument to su
. For example, to switch to the user tyrion
you would type:
su tyrion
Sudo vs. Su #
On some Linux distributions like Ubuntu, the root user account
is disabled by default for security reasons. This means that no password is set for root, and you cannot use su
to switch to root.
su
command with sudo
and enter the currently logged in user password:
The sudo
command allows you to run programs as another user, by default the root user.
If the user is granted with sudo
assess, the su
command is invoked as root. Running sudo su -
and then typing the user password has the same effect the same as running su -
and typing the root password.
When used with the -i
option, sudo
run an interactive login shell with the root user’s environment:
sudo -i
is basically the same as running su -
.
The advantage of using sudo
over su
is that the root password doesn’t need to be shared among multiple administrative user accounts.
With sudo
you can also allow users to run only specific programs with root privileges.
Conclusion #
su
is a command-line utility that allows you to temporarily become another user and execute commands with the substitute user.
If you have any questions or feedback, feel free to leave a comment.
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