NAME
setuid - run a command with a different uid.
SYNOPSIS
setuid username|uid command [ args ]
DESCRIPTION
Setuid changes user id, then executes the specified command. Unlike
some versions of su(1), this program doesn’t ever ask for a password
when executed with effective uid=root. This program doesn’t change the
environment; it only changes the uid and then uses execvp() to find the
command in the path, and execute it. (If the command is a script,
execvp() passes the command name to /bin/sh for processing.)
For example,
setuid some_user $SHELL
can be used to start a shell running as another user.
Setuid is useful inside scripts that are being run by a setuid-root
user — such as a script invoked with super, so that the script can
execute some commands using the uid of the original user, instead of
root. This allows unsafe commands (such as editors and pagers) to be
used in a non-root mode inside a super script. For example, an
operator with permission to modify a certain protected_file could use a
super command that simply does:
cp protected_file temp_file
setuid $ORIG_USER ${EDITOR:-/bin/vi} temp_file
cp temp_file protected_file
(Note: don’t use this example directly. If the temp_file can somehow
be replaced by another user, as might be the case if it’s kept in a
temporary directory, there will be a race condition in the time between
editing the temporary file and copying it back to the protected file.)
AUTHOR
Will Deich
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