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+'\" t
+.\" Title: su
+.\" Author: Julianne Frances Haugh
+.\" Generator: DocBook XSL Stylesheets v1.76.1 <http://docbook.sf.net/>
+.\" Date: 05/25/2012
+.\" Manual: User Commands
+.\" Source: shadow-utils 4.1.5.1
+.\" Language: English
+.\"
+.TH "SU" "1" "05/25/2012" "shadow\-utils 4\&.1\&.5\&.1" "User Commands"
+.\" -----------------------------------------------------------------
+.\" * Define some portability stuff
+.\" -----------------------------------------------------------------
+.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+.\" http://bugs.debian.org/507673
+.\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
+.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+.ie \n(.g .ds Aq \(aq
+.el .ds Aq '
+.\" -----------------------------------------------------------------
+.\" * set default formatting
+.\" -----------------------------------------------------------------
+.\" disable hyphenation
+.nh
+.\" disable justification (adjust text to left margin only)
+.ad l
+.\" -----------------------------------------------------------------
+.\" * MAIN CONTENT STARTS HERE *
+.\" -----------------------------------------------------------------
+.SH "NAME"
+su \- change user ID or become superuser
+.SH "SYNOPSIS"
+.HP \w'\fBsu\fR\ 'u
+\fBsu\fR [\fIoptions\fR] [\fIusername\fR]
+.SH "DESCRIPTION"
+.PP
+The
+\fBsu\fR
+command is used to become another user during a login session\&. Invoked without a
+\fBusername\fR,
+\fBsu\fR
+defaults to becoming the superuser\&. The optional argument
+\fB\-\fR
+may be used to provide an environment similar to what the user would expect had the user logged in directly\&.
+.PP
+Additional arguments may be provided after the username, in which case they are supplied to the user\*(Aqs login shell\&. In particular, an argument of
+\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
+/etc/passwd
+for the target user\&.
+.PP
+You can use the
+\fB\-\-\fR
+argument to separate
+\fBsu\fR
+options from the arguments supplied to the shell\&.
+.PP
+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\&.
+.PP
+The current environment is passed to the new shell\&. The value of
+\fB$PATH\fR
+is reset to
+/bin:/usr/bin
+for normal users, or
+/sbin:/bin:/usr/sbin:/usr/bin
+for the superuser\&. This may be changed with the
+\fBENV_PATH\fR
+and
+\fBENV_SUPATH\fR
+definitions in
+/etc/login\&.defs\&.
+.PP
+A subsystem login is indicated by the presence of a "*" as the first character of the login shell\&. The given home directory will be used as the root of a new file system which the user is actually logged into\&.
+.SH "OPTIONS"
+.PP
+The options which apply to the
+\fBsu\fR
+command are:
+.PP
+\fB\-c\fR, \fB\-\-command\fR \fICOMMAND\fR
+.RS 4
+Specify a command that will be invoked by the shell using its
+\fB\-c\fR\&.
+.sp
+The executed command will have no controlling terminal\&. This option cannot be used to execute interractive programs which need a controlling TTY\&.
+.RE
+.PP
+\fB\-\fR, \fB\-l\fR, \fB\-\-login\fR
+.RS 4
+Provide an environment similar to what the user would expect had the user logged in directly\&.
+.sp
+When
+\fB\-\fR
+is used, it must be specified as the last
+\fBsu\fR
+option\&. The other forms (\fB\-l\fR
+and
+\fB\-\-login\fR) do not have this restriction\&.
+.RE
+.PP
+\fB\-s\fR, \fB\-\-shell\fR \fISHELL\fR
+.RS 4
+The shell that will be invoked\&.
+.sp
+The invoked shell is chosen from (highest priority first):
+.PP
+.RS 4
+The shell specified with \-\-shell\&.
+.RE
+.PP
+.RS 4
+If
+\fB\-\-preserve\-environment\fR
+is used, the shell specified by the
+\fB$SHELL\fR
+environment variable\&.
+.RE
+.PP
+.RS 4
+The shell indicated in the
+/etc/passwd
+entry for the target user\&.
+.RE
+.PP
+.RS 4
+/bin/sh
+if a shell could not be found by any above method\&.
+.RE
+.sp
+If the target user has a restricted shell (i\&.e\&. the shell field of this user\*(Aqs entry in
+/etc/passwd
+is not listed in
+/etc/shells), then the
+\fB\-\-shell\fR
+option or the
+\fB$SHELL\fR
+environment variable won\*(Aqt be taken into account, unless
+\fBsu\fR
+is called by root\&.
+.RE
+.PP
+\fB\-m\fR, \fB\-p\fR, \fB\-\-preserve\-environment\fR
+.RS 4
+Preserve the current environment, except for:
+.PP
+\fB$PATH\fR
+.RS 4
+reset according to the
+/etc/login\&.defs
+options
+\fBENV_PATH\fR
+or
+\fBENV_SUPATH\fR
+(see below);
+.RE
+.PP
+\fB$IFS\fR
+.RS 4
+reset to
+\(lq<space><tab><newline>\(rq, if it was set\&.
+.RE
+.sp
+If the target user has a restricted shell, this option has no effect (unless
+\fBsu\fR
+is called by root)\&.
+.sp
+Note that the default behavior for the environment is the following:
+.PP
+.RS 4
+The
+\fB$HOME\fR,
+\fB$SHELL\fR,
+\fB$USER\fR,
+\fB$LOGNAME\fR,
+\fB$PATH\fR, and
+\fB$IFS\fR
+environment variables are reset\&.
+.RE
+.PP
+.RS 4
+If
+\fB\-\-login\fR
+is not used, the environment is copied, except for the variables above\&.
+.RE
+.PP
+.RS 4
+If
+\fB\-\-login\fR
+is used, the
+\fB$TERM\fR,
+\fB$COLORTERM\fR,
+\fB$DISPLAY\fR, and
+\fB$XAUTHORITY\fR
+environment variables are copied if they were set\&.
+.RE
+.PP
+.RS 4
+If
+\fB\-\-login\fR
+is used, the
+\fB$TZ\fR,
+\fB$HZ\fR, and
+\fB$MAIL\fR
+environment variables are set according to the
+/etc/login\&.defs
+options
+\fBENV_TZ\fR,
+\fBENV_HZ\fR,
+\fBMAIL_DIR\fR, and
+\fBMAIL_FILE\fR
+(see below)\&.
+.RE
+.PP
+.RS 4
+If
+\fB\-\-login\fR
+is used, other environment variables might be set by the
+\fBENVIRON_FILE\fR
+file (see below)\&.
+.RE
+.sp
+.RE
+.SH "CAVEATS"
+.PP
+This version of
+\fBsu\fR
+has many compilation options, only some of which may be in use at any particular site\&.
+.SH "CONFIGURATION"
+.PP
+The following configuration variables in
+/etc/login\&.defs
+change the behavior of this tool:
+.PP
+\fBCONSOLE\fR (string)
+.RS 4
+If defined, either full pathname of a file containing device names (one per line) or a ":" delimited list of device names\&. Root logins will be allowed only upon these devices\&.
+.sp
+If not defined, root will be allowed on any device\&.
+.sp
+The device should be specified without the /dev/ prefix\&.
+.RE
+.PP
+\fBCONSOLE_GROUPS\fR (string)
+.RS 4
+List of groups to add to the user\*(Aqs supplementary groups set when logging in on the console (as determined by the CONSOLE setting)\&. Default is none\&.
+
+Use with caution \- it is possible for users to gain permanent access to these groups, even when not logged in on the console\&.
+.RE
+.PP
+\fBDEFAULT_HOME\fR (boolean)
+.RS 4
+Indicate if login is allowed if we can\*(Aqt cd to the home directory\&. Default is no\&.
+.sp
+If set to
+\fIyes\fR, the user will login in the root (/) directory if it is not possible to cd to her home directory\&.
+.RE
+.PP
+\fBENV_HZ\fR (string)
+.RS 4
+If set, it will be used to define the HZ environment variable when a user login\&. The value must be preceded by
+\fIHZ=\fR\&. A common value on Linux is
+\fIHZ=100\fR\&.
+.RE
+.PP
+\fBENVIRON_FILE\fR (string)
+.RS 4
+If this file exists and is readable, login environment will be read from it\&. Every line should be in the form name=value\&.
+.sp
+Lines starting with a # are treated as comment lines and ignored\&.
+.RE
+.PP
+\fBENV_PATH\fR (string)
+.RS 4
+If set, it will be used to define the PATH environment variable when a regular user login\&. The value is a colon separated list of paths (for example
+\fI/bin:/usr/bin\fR) and can be preceded by
+\fIPATH=\fR\&. The default value is
+\fIPATH=/bin:/usr/bin\fR\&.
+.RE
+.PP
+\fBENV_SUPATH\fR (string)
+.RS 4
+If set, it will be used to define the PATH environment variable when the superuser login\&. The value is a colon separated list of paths (for example
+\fI/sbin:/bin:/usr/sbin:/usr/bin\fR) and can be preceded by
+\fIPATH=\fR\&. The default value is
+\fIPATH=/sbin:/bin:/usr/sbin:/usr/bin\fR\&.
+.RE
+.PP
+\fBENV_TZ\fR (string)
+.RS 4
+If set, it will be used to define the TZ environment variable when a user login\&. The value can be the name of a timezone preceded by
+\fITZ=\fR
+(for example
+\fITZ=CST6CDT\fR), or the full path to the file containing the timezone specification (for example
+/etc/tzname)\&.
+.sp
+If a full path is specified but the file does not exist or cannot be read, the default is to use
+\fITZ=CST6CDT\fR\&.
+.RE
+.PP
+\fBLOGIN_STRING\fR (string)
+.RS 4
+The string used for prompting a password\&. The default is to use "Password: ", or a translation of that string\&. If you set this variable, the prompt will not be translated\&.
+.sp
+If the string contains
+\fI%s\fR, this will be replaced by the user\*(Aqs name\&.
+.RE
+.PP
+\fBMAIL_CHECK_ENAB\fR (boolean)
+.RS 4
+Enable checking and display of mailbox status upon login\&.
+.sp
+You should disable it if the shell startup files already check for mail ("mailx \-e" or equivalent)\&.
+.RE
+.PP
+\fBMAIL_DIR\fR (string)
+.RS 4
+The mail spool directory\&. This is needed to manipulate the mailbox when its corresponding user account is modified or deleted\&. If not specified, a compile\-time default is used\&.
+.RE
+.PP
+\fBMAIL_FILE\fR (string)
+.RS 4
+Defines the location of the users mail spool files relatively to their home directory\&.
+.RE
+.PP
+The
+\fBMAIL_DIR\fR
+and
+\fBMAIL_FILE\fR
+variables are used by
+\fBuseradd\fR,
+\fBusermod\fR, and
+\fBuserdel\fR
+to create, move, or delete the user\*(Aqs mail spool\&.
+.PP
+If
+\fBMAIL_CHECK_ENAB\fR
+is set to
+\fIyes\fR, they are also used to define the
+\fBMAIL\fR
+environment variable\&.
+.PP
+\fBQUOTAS_ENAB\fR (boolean)
+.RS 4
+Enable setting of resource limits from
+/etc/limits
+and ulimit, umask, and niceness from the user\*(Aqs passwd gecos field\&.
+.RE
+.PP
+\fBSULOG_FILE\fR (string)
+.RS 4
+If defined, all su activity is logged to this file\&.
+.RE
+.PP
+\fBSU_NAME\fR (string)
+.RS 4
+If defined, the command name to display when running "su \-"\&. For example, if this is defined as "su" then a "ps" will display the command is "\-su"\&. If not defined, then "ps" would display the name of the shell actually being run, e\&.g\&. something like "\-sh"\&.
+.RE
+.PP
+\fBSU_WHEEL_ONLY\fR (boolean)
+.RS 4
+If
+\fIyes\fR, the user must be listed as a member of the first gid 0 group in
+/etc/group
+(called
+\fIroot\fR
+on most Linux systems) to be able to
+\fBsu\fR
+to uid 0 accounts\&. If the group doesn\*(Aqt exist or is empty, no one will be able to
+\fBsu\fR
+to uid 0\&.
+.RE
+.PP
+\fBSYSLOG_SU_ENAB\fR (boolean)
+.RS 4
+Enable "syslog" logging of
+\fBsu\fR
+activity \- in addition to sulog file logging\&.
+.RE
+.PP
+\fBUSERGROUPS_ENAB\fR (boolean)
+.RS 4
+Enable setting of the umask group bits to be the same as owner bits (examples: 022 \-> 002, 077 \-> 007) for non\-root users, if the uid is the same as gid, and username is the same as the primary group name\&.
+.sp
+If set to
+\fIyes\fR,
+\fBuserdel\fR
+will remove the user\*(Aqs group if it contains no more members, and
+\fBuseradd\fR
+will create by default a group with the name of the user\&.
+.RE
+.SH "FILES"
+.PP
+/etc/passwd
+.RS 4
+User account information\&.
+.RE
+.PP
+/etc/shadow
+.RS 4
+Secure user account information\&.
+.RE
+.PP
+/etc/login\&.defs
+.RS 4
+Shadow password suite configuration\&.
+.RE
+.SH "EXIT VALUES"
+.PP
+On success,
+\fBsu\fR
+returns the exit value of the command it executed\&.
+.PP
+If this command was terminated by a signal,
+\fBsu\fR
+returns the number of this signal plus 128\&.
+.PP
+If su has to kill the command (because it was asked to terminate, and the command did not terminate in time),
+\fBsu\fR
+returns 255\&.
+.PP
+Some exit values from
+\fBsu\fR
+are independent from the executed command:
+.PP
+\fI0\fR
+.RS 4
+success (\fB\-\-help\fR
+only)
+.RE
+.PP
+\fI1\fR
+.RS 4
+System or authentication failure
+.RE
+.PP
+\fI126\fR
+.RS 4
+The requested command was not found
+.RE
+.PP
+\fI127\fR
+.RS 4
+The requested command could not be executed
+.RE
+.SH "SEE ALSO"
+.PP
+\fBlogin\fR(1),
+\fBlogin.defs\fR(5),
+\fBsg\fR(1),
+\fBsh\fR(1)\&.