251 lines
6.7 KiB
Groff
251 lines
6.7 KiB
Groff
.\" Copyright (c) 1988, 1990, 1993, 1994
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)su.1 8.2 (Berkeley) 4/18/94
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.\" $FreeBSD$
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.\"
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.Dd March 26, 2020
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.Dt SU 1
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.Os
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.Sh NAME
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.Nm su
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.Nd substitute user identity
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.Sh SYNOPSIS
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.Nm
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.Op Fl
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.Op Fl c Ar class
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.Op Fl flms
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.Op Ar login Op Ar args
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.Sh DESCRIPTION
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The
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.Nm
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utility requests appropriate user credentials via PAM
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and switches to that user ID
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(the default user is the superuser).
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A shell is then executed.
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.Pp
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PAM is used to set the policy
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.Xr su 1
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will use.
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In particular, by default only users in the
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.Dq Li wheel
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group can switch to UID 0
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.Pq Dq Li root .
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This group requirement may be changed by modifying the
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.Dq Li pam_group
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section of
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.Pa /etc/pam.d/su .
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See
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.Xr pam_group 8
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for details on how to modify this setting.
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.Pp
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By default, the environment is unmodified with the exception of
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.Ev USER ,
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.Ev HOME ,
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and
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.Ev SHELL .
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.Ev HOME
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and
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.Ev SHELL
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are set to the target login's default values.
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.Ev USER
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is set to the target login, unless the target login has a user ID of 0,
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in which case it is unmodified.
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The invoked shell is the one belonging to the target login.
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This is the traditional behavior of
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.Nm .
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Resource limits and session priority applicable to the original user's
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login class (see
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.Xr login.conf 5 )
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are also normally retained unless the target login has a user ID of 0.
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.Pp
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The options are as follows:
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.Bl -tag -width Ds
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.It Fl c Ar class
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Use the settings of the specified login class.
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The login class must be defined in
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.Xr login.conf 5 .
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Only allowed for the super-user.
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.It Fl f
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If the invoked shell is
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.Xr csh 1 ,
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this option prevents it from reading the
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.Dq Pa .cshrc
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file.
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.It Fl l
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Simulate a full login.
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The environment is discarded except for
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.Ev HOME ,
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.Ev SHELL ,
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.Ev PATH ,
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.Ev TERM ,
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and
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.Ev USER .
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.Ev HOME
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and
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.Ev SHELL
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are modified as above.
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.Ev USER
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is set to the target login.
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.Ev PATH
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is set to
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.Dq Pa /bin:/usr/bin .
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.Ev TERM
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is imported from your current environment.
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Environment variables may be set or overridden from the login class
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capabilities database according to the class of the target login.
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The invoked shell is the target login's, and
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.Nm
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will change directory to the target login's home directory.
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Resource limits and session priority are modified to that for the
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target account's login class.
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.It Fl
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(no letter) The same as
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.Fl l .
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.It Fl m
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Leave the environment unmodified.
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The invoked shell is your login shell, and no directory changes are made.
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As a security precaution, if the target user's shell is a non-standard
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shell (as defined by
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.Xr getusershell 3 )
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and the caller's real uid is
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non-zero,
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.Nm
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will fail.
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.It Fl s
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Set the MAC label to the user's default label as part of the user
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credential setup.
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Setting the MAC label may fail if the MAC label of the invoking process
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is not sufficient to transition to the user's default MAC label.
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If the label cannot be set,
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.Nm
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will fail.
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.El
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.Pp
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The
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.Fl l
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(or
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.Fl )
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and
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.Fl m
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options are mutually exclusive; the last one specified
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overrides any previous ones.
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.Pp
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If the optional
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.Ar args
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are provided on the command line, they are passed to the login shell of
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the target login.
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Note that all command line arguments before the target login name are
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processed by
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.Nm
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itself, everything after the target login name gets passed to the login
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shell.
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.Pp
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By default (unless the prompt is reset by a startup file) the super-user
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prompt is set to
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.Dq Sy \&#
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to remind one of its awesome power.
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.Sh ENVIRONMENT
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Environment variables used by
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.Nm :
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.Bl -tag -width HOME
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.It Ev HOME
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Default home directory of real user ID unless modified as
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specified above.
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.It Ev PATH
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Default search path of real user ID unless modified as specified above.
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.It Ev TERM
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Provides terminal type which may be retained for the substituted
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user ID.
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.It Ev USER
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The user ID is always the effective ID (the target user ID) after an
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.Nm
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unless the user ID is 0 (root).
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.El
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.Sh FILES
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.Bl -tag -width "/etc/pam.d/su" -compact
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.It Pa /etc/pam.d/su
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PAM configuration for
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.Nm .
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.El
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.Sh EXAMPLES
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.Bl -tag -width 5n -compact
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.It Li "su -m operator -c poweroff"
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Starts a shell as user
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.Li operator ,
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and runs the command
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.Li poweroff .
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You will be asked for operator's password unless your real UID is 0.
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Note that the
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.Fl m
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option is required since user
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.Dq operator
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does not have a valid shell by default.
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In this example,
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.Fl c
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is passed to the shell of the user
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.Dq operator ,
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and is not interpreted as an argument to
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.Nm .
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.It Li "su -m operator -c 'shutdown -p now'"
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Same as above, but the target command consists of more than a
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single word and hence is quoted for use with the
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.Fl c
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option being passed to the shell.
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(Most shells expect the argument to
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.Fl c
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to be a single word).
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.It Li "su -m -c staff operator -c 'shutdown -p now'"
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Same as above, but the target command is run with the resource limits of
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the login class
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.Dq staff .
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Note: in this example, the first
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.Fl c
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option applies to
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.Nm
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while the second is an argument to the shell being invoked.
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.It Li "su -l foo"
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Simulate a login for user foo.
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.It Li "su - foo"
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Same as above.
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.It Li "su -"
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Simulate a login for root.
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.El
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.Sh SEE ALSO
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.Xr csh 1 ,
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.Xr sh 1 ,
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.Xr group 5 ,
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.Xr login.conf 5 ,
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.Xr passwd 5 ,
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.Xr environ 7 ,
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.Xr pam_group 8
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.Sh HISTORY
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A
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.Nm
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command appeared in
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.At v1 .
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