How do I run a command as the system administrator (root)

I need to run a command with administrative privileges. Someone said I should run a command as root. How do I do this?

ANSWER:-

The main two commandline possibilities are:

Use su and enter the root password when prompted.
Put sudo in front of the command, and enter your password when prompted.
Running a shell command as root
sudo (preferred when not running a graphical display)
This is the preferred method on most systems, including Ubuntu, Linux Mint, (arguably) Debian, and others. If you don't know a separate root password, use this method.

Sudo requires that you type your own password. (The purpose is to limit the damage if you leave your keyboard unattended and unlocked, and also to ensure that you really wish to run that command and it wasn't e.g. a typo.) It is often configured to not ask again for a few minutes so you can run severalsudo commands in succession.

Example:

sudo service apache restart
If you need to run several commands as root, prefix each of them with sudo. Sometimes, it is more convenient to run an interactive shell as root. You can use sudo -i for that:

$ sudo -i
# command 1
# command 2
...
# exit
Instead of sudo -i, you can use sudo -s. The difference is that -i reinitializes the environment to sane defaults, whereas -s uses your configuration files for better or for worse.

For more information, see the sudo website, or type man sudo on your system. Sudo is very configurable; for example it can be configured to let a certain user only execute certain commands as root. Read the sudoers man page for more information; use sudo visudo to edit the sudoers file.

su
The su command exists on most unix-like systems. It lets you run a command as another user, provided you know that user's password. When run with no user specified, su will default to the root account.

Example:

su -c 'service apache restart'
The command to run must be passed using the -c option. Note that you need quotes so that the command is not parsed by your shell, but passed intact to the root shell that su runs.

To run multiple commands as root, it is more convenient to start an interactive shell.

$ su
# command 1
# command 2
...
# exit
On some systems, you need to be in group number 0 (called wheel) to use su. (The point is to limit the damage if the root password is accidentally leaked to someone.)

Logging in as root
If there is a root password set and you are in possession of it, you can simply type root at the login prompt and enter the root password. Be very careful, and avoid running complex applications as root as they might do something you didn't intend. Logging in directly as root is mainly useful in emergency situations, such as disk failures or when you've locked yourself out of your account.

Single User Mode
Single user mode, or run-level 1, also gives you root privileges. This is intended primarily for emergency maintenance situations where booting into a multi-user run-level is not possible. You can boot into single user mode by passing single or emergency on the kernel command line. Note that booting into single-user mode is not the same as booting the system normally and logging in as root. Rather, the system will only start the services defined for run-level 1. Typically, this is the smallest number of services required to have a usable system.

You can also get to single user mode by using the telinit command: telinit 1; however, this command requires you to already have gotten root privileges via some other method in order to run.

On many systems booting into single user mode will give the user access to a root shell without prompting for a password. Notably, systemd-based systems will prompt you for the root password when you boot this way.

Other programs
Calife
Calife lets you run commands as another user by typing your own password, if authorized. It is similar to the much more widespread sudo (see above). Calife is more light-weight than sudo but also less configurable.

Op
Op lets you run commands as another user, including root. This not a full-blown tool to run arbitrary commands: you type op followed by a mnemonic configured by the system administrator to run a specific command.

Super
Super lets you run commands as another user, including root. The command must have been allowed by the system administrator.

Running a graphical command as root
See also Wikipedia.

PolicyKit (preferred when using GNOME)
Simply prefix your desired command with the command pkexec. Be aware that while this works in most cases, it does not work universally.

See man pkexec for more information.

KdeSu, KdeSudo (preferred when using KDE)
kdesu and kdesudo are graphical front-ends to su and sudo respectively. They allow you to run X Window programs as root with no hassle. They are part of KDE. Type

kdesu -c 'command --option argument'
and enter the root password, or type

kdesudo -c 'command --option argument'
and enter your password (if authorized to run sudo). If you check the “keep password” option in KdeSu, you will only have to type the root password once per login session.

Other programs
Ktsuss
Ktsuss (“keep the su simple, stupid”) is a graphical version of su.

Beesu
Beesu is a graphical front-end to the su command that has replaced Gksu in Red Hat-based operating systems. It has been developed mainly for RHEL and Fedora.

Obsolete methods
gksu and gksudo
gksu and gksudo are graphical front-ends to su and sudo respectively. They allow you to run X Window programs as root with no hassle. They are part of Gnome. Type

gksu command --option argument
and enter the root password, or type

gksudo command --option argument
and enter your password (if authorized to run sudo).

gksu and gksudo are obsolete. They have been replaced by PolicyKit in GNOME, and many distributions (such as Ubuntu) no longer install them by default. You should not depend on them being available or working properly.

Manually via one of the shell-based methods
Use one of the methods in the "running a shell command as root section". You will need to ensure that neither the DISPLAY environment variable nor the XAUTHORITY environment get reset during the transition to root. This may require additional configuration of those methods that is outside the scope of this question.

Overall, this is a bad idea, mostly because graphical applications will read and write configuration files as root, and when you try to use those applications again as your normal user, those applications won't have permission to read their own configurations.

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