su

The su (substitute user) command can be used to adopt the privileges of other users from the system.

The command is provided by the util-linux package, that has the su USE flag enabled by default. The su command is also available with sys-apps/shadow , that also has a su USE flag. Avoid installing both these commands simultaneously.

Caveats

The use of su to access the user root is only permitted when the calling user is a member of the user group wheel.

In the next example the user john is added to the user group wheel.

Usage

Usage:
 su [options] [-] [<user> [<argument>...]]
 
Change the effective user ID and group ID to that of <user>.
A mere - implies -l. If <user> is not given, root is assumed.
 
Options:
 -m, -p, --preserve-environment do not reset environment variables
 -w, --whitelist-environment <list> don't reset specified variables
 
 -g, --group <group> specify the primary group
 -G, --supp-group <group> specify a supplemental group
 
 -, -l, --login make the shell a login shell
 -c, --command <command> pass a single command to the shell with -c
 --session-command <command> pass a single command to the shell with -c
 and do not create a new session
 -f, --fast pass -f to the shell (for csh or tcsh)
 -s, --shell <shell> run <shell> if /etc/shells allows it
 -P, --pty create a new pseudo-terminal
 
 -h, --help display this help
 -V, --version display version
 
For more details see su(1).

Adopt root privileges

su will run commands as root by default. Since not specifying a username will cause su to ask for root privileges, the following command will run as root and halt the system:

Adopt another user's privileges

It is also possible to specify a user other than root to substitute commands. The following example will run the command echo as the user larry:

See also

• doas — provides a way to perform commands as another user.
• sudo — provides a simple and secure way to configure privilege escalation

• Command line tools