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.TH "SU" "1" "01/22/2006" "User Commands" "User Commands"
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. \" disable hyphenation
.nh
. \" disable justification (adjust text to left margin only)
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.ad l
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.SH "NAME"
su \- change user ID or become super\- user
.SH "SYNOPSIS"
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.HP 3
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\fB su\fR [\fI options\fR ] [\- ] [\fI username\fR \ [\ \fIargs\fR\ ]]
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.SH "DESCRIPTION"
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.PP
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\fB su\fR
is used to become another user during a login session. Invoked without a username,
\fB su\fR
defaults to becoming the super user. The optional argument
\fB \- \fR
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may be used to provide an environment similar to what the user would expect had the user logged in directly.
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.PP
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Additional arguments may be provided after the username, in which case they are supplied to the user's login shell. In particular, an argument of
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\fB \- c\fR
will cause the next argument to be treated as a command by most command interpreters. The command will be executed by the shell specified in
\fI /etc/passwd\fR
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for the target user.
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.PP
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You can use the
\fB \- \- \fR
argument to separate
\fB su\fR
options from the arguments supplied to the shell.
.PP
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The user will be prompted for a password, if appropriate. Invalid passwords will produce an error message. All attempts, both valid and invalid, are logged to detect abuse of the system.
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.PP
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The current environment is passed to the new shell. The value of
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\fB $PATH\fR
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is reset to
\fI /bin:/usr/bin\fR
for normal users, or
\fI /sbin:/bin:/usr/sbin:/usr/bin\fR
for the super user. This may be changed with the
\fI ENV_PATH\fR
and
\fI ENV_SUPATH\fR
definitions in
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\fI /etc/login.defs\fR .
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.PP
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A subsystem login is indicated by the presence of a "*" as the first character of the login shell. The given home directory will be used as the root of a new file system which the user is actually logged into.
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.SH "OPTIONS"
.PP
The options which apply to the
\fB su\fR
command are:
.TP
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\fB \- c\fR , \fB \- \- command\fR \fI SHELL\fR
Specify a command that will be invoked by the shell using its
\fB \- c\fR .
.TP
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\fB \- \fR , \fB \- l\fR , \fB \- \- login\fR
Provide an environment similar to what the user would expect had the user logged in directly.
.sp
When
\fB \- \fR
is used, it must be specified as the last
\fB su\fR
option. The other forms (\fB \- l\fR
and
\fB \- \- login\fR ) do not have this restriction.
.TP
\fB \- s\fR , \fB \- \- shell\fR \fI SHELL\fR
The shell that will be invoked.
.sp
The invoked shell is choosen among (higest priority first):
.RS
.TP 3
\(bu
The shell specified with \- \- shell
.TP
\(bu
If
\fB \- \- preserve\- environment\fR
is used, the shell specified by the
\fB $SHELL\fR
environment variable.
.TP
\(bu
The shell indicated in the /etc/passwd entry for the target user.
.TP
\(bu
/bin/sh if a shell could not be found by any above method.
.RE
.IP
.sp
If the target user has a restricted shell (i.e. the shell field of this user's entry in
\fI /etc/passwd\fR
is not specified in
\fI /etc/shell\fR ), then the
\fB \- \- shell\fR
option or the
\fB $SHELL\fR
environment variable won't be taken into account unless
\fB su\fR
is called by the root.
.TP
\fB \- m\fR , \fB \- p\fR , \fB \- \- preserve\- environment\fR
Preserve the current environment.
.sp
If the target user has a restricted shell, this option has no effect (unless
\fB su\fR
is called by root).
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.SH "CAVEATS"
.PP
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This version of
\fB su\fR
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has many compilation options, only some of which may be in use at any particular site.
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.SH "FILES"
.TP
\fI /etc/passwd\fR
user account information
.TP
\fI /etc/shadow\fR
secure user account information
.SH "SEE ALSO"
.PP
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\fB login\fR (1),
\fB login.defs\fR (5),
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\fB sh\fR (1)