NAME

su − become super-user or another user

SYNOPSIS

su [ − ] [ name [ arg ... ] ]

DESCRIPTION

Su allows one to become another user without logging off.  The default user name is root (i.e., super-user). 

To use su, the appropriate password must be supplied (unless one is already root).  If the password is correct, su will execute a new shell with the real and effective user ID, real and effective group ID, and group access list set to that of the specified user.  The new shell will be the optional program named in the shell field of the specified user’s password file entry (see passwd(4)), or /bin/sh if none is specified (see sh(1)). To restore normal user ID privileges, type an EOF to the new shell. 

Any additional arguments given on the command line are passed to the program invoked as the shell, permitting the super-user to run shell procedures with restricted privileges.  When using programs like sh(1), an arg of the form −c string executes string via the shell and an arg of −r will give the user a restricted shell. 

The following statements are true only if the optional program named in the shell field of the specified user’s password file entry is like sh(1).  If the first argument to su is a −, the environment will be changed to what would be expected if the user actually logged in as the specified user.  This is done by invoking the program used as the shell with an arg0 value whose first character is −, thus causing first the system’s profile (/etc/profile) and then the specified user’s profile (.profile in the new HOME directory) to be executed.  Otherwise, the environment is passed along unchanged, except that $PATH, is unconditionally set to /bin:/etc:/usr/bin for root.  Note that if the optional program used as the shell is /bin/sh, the user’s .profile can check arg0 for −sh or −su to determine if it was invoked by login(1) or su(1), respectively.  If the user’s program is other than /bin/sh, then .profile is invoked with an arg0 of -program by both login(1) and su(1). 

The − option always resets $PATH to /bin:/etc:/usr/bin for the super-user, and /bin:/usr/bin for all others.  However, the files /etc/profile and .profile are normally executed anyway, thus restoring the intended value of $PATH. 

All attempts to become another user are logged in /usr/adm/sulog, including failures.  Successful attempts are flagged with "+", failures with "-". 

EXAMPLES

To become user bin while retaining your previously exported environment, execute:

su bin

To become user bin but change the environment to what would be expected if bin had originally logged in, execute:

su - bin

To execute command with the temporary environment and permissions of user bin, type:

su - bin -c "command args"

FILES

$HOME/.profile user’s profile

/etc/logingroup system’s default group access list file

/etc/passwd system’s password file

/etc/profile system’s profile

/usr/adm/sulog log of all attempts

VARIABLES

HOME the user’s home directory

LOGNAME the user’s login name

PATH the command name search path

PS1 the default prompt

SHELL the name of the user’s shell

SEE ALSO

env(1), login(1), sh(1), initgroups(3C), group(4), passwd(4), profile(4), environ(5). 

Hewlett-Packard Company  —  Version B.1,  May 11, 2021