really - gain privilege or run commands a different user
SYNOPSIS
really [ options ] [ command args... ]
DESCRIPTION
really checks whether the caller is allowed, and if it is it changes its uids
and gids according to the command line options and executes the
specified command.
If no options are specified, the uid will be set to 0 and the gids
will be left unchanged.
If no command is specified,
really will run
"$SHELL -i" .
A caller is allowed if it has write access to
/etc/inittab . This is most easily achieved by creating or using a suitable group,
containing all the appropriate users, and making
/etc/inittab group-owned by that group and group-writeable.
OPTIONS
-uusername | --userusername
Sets the uid, gid, and supplementary group list, according to
username 's entry in the password and group databases.
-iusername | --useronlyusername
Sets only the uid according to
username 's entry in the password database.
-Iuid | --uidonlyuid
Sets the uid to the numeric value
uid (which need not correspond to any existing user in the password
database).
-ggroupname | --groupgroupname
groupname is looked up in the group database and its gid is appended to the
process's supplementary groups list. If this is the first gid
specified it will also be set as the primary gid.
-Ggid | --gidgid
gid is appended to the process's supplementary groups list.
( gid need not correspond to any existing group in the group database.) If
this is the first gid specified it will also be set as the primary
gid.
-z | --groupsclear
Clears the process's supplementary groups list. When using this
option you must also specify
-g or
-G . The process's groups will then be exactly those specified. The
relative position of
-z in the argument list is not relevant.
--
Indicates the end of the options. The next argument (if present) will
be interpreted as the command name, even if it starts with a hyphen.
SECURITY CONSIDERATIONS
really is designed so that installing it setuid root is extremely unlikely to
compromise the security of any system. It will check using
access(2) whether the real user is allowed to write to
/etc/inittab and if this check fails
really will exit without even attempting to parse its command line.
really is
not designed to be resistant to malicious command line arguments. Do not
allow untrusted processes to pass options to really, or to specify the
command to be run. Whether it is safe to allow relatively untrusted
processes to pass options to the command which is to be run depends on
the behaviour of that command and its security status.
Attempting to use
really to drop privilege is dangerous unless the calling environment is very
well understood. There are many inherited process properties and
resources which might be used by the callee to escalate its privilege
to that of the (root-equivalent) caller. For this function, it is
usually better to use
userv if possible.
ENVIRONMENT
really does not manipulate the environment at all. The calling program is
run in exactly the same environment as the caller passes to
really . In particular,
really will not add
sbin directories to
PATH so
really -enabled accounts will usually need to have these directories on their
configured
PATH to start with.
SHELL is used to find the default shell to use in interactive mode (ie, when
no command is specified).
AUTHOR
This version of
really was written by Ian Jackson <ian@chiark.greenend.org.uk>.
It and this manpage are Copyright (C) 1992-5,2003 Ian Jackson
<ian@chiark.greenend.org.uk>.
really is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2,
or (at your option) any later version.
really is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public
License along with this file; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
AVAILABILITY
really is currently part of
chiark-utils and is available for download from
ftp.chiark.greenend.org.uk in /users/ian/chiark-utils/,
in source and pre-compiled binary form, and also from Ian Jackson's
cvsweb.