1 .TH really 8 2001-10-21 chiark-backup
3 really \- gain privilege or run commands a different user
7 .RI [ "command args... " ]
10 checks whether the caller is allowed, and if it is it changes its uids
11 and gids (and perhaps root directory) according to the command line
12 options and executes the specified command.
14 If no options are specified, the uid will be set to 0 and the gids
15 and root directory will be left unchanged.
17 If no command is specified,
22 A caller is allowed if it has write access to
24 and is also member of the group
26 This is most easily achieved by making inittab group-writeable by some
27 suitable group containing all the appropriate users, and making
29 group-owned by that group and group-writeable. The root group is
30 perhaps a good choice if it isn't being used for anything else.
33 \fB-u\fR \fIusername\fR | \fB--user\fR \fIusername\fR
34 Sets the uid, gid, and supplementary group list, according to
36 entry in the password and group databases.
38 \fB-i\fR \fIusername\fR | \fB--useronly\fR \fIusername\fR
39 Sets only the uid according to
41 entry in the password database.
43 \fB-I\fR \fIuid\fR | \fB--uidonly\fR \fIuid\fR
44 Sets the uid to the numeric value
46 (which need not correspond to any existing user in the password
49 \fB-g\fR \fIgroupname\fR | \fB--group\fR \fIgroupname\fR
51 is looked up in the group database and its gid is appended to the
52 process's supplementary groups list. If this is the first gid
53 specified it will also be set as the primary gid.
55 \fB-G\fR \fIgid\fR | \fB--gid\fR \fIgid\fR
57 is appended to the process's supplementary groups list.
59 need not correspond to any existing group in the group database.) If
60 this is the first gid specified it will also be set as the primary
63 \fB-z\fR | \fB--groupsclear\fR
64 Clears the process's supplementary groups list. When using this
65 option you must also specify
69 The process's groups will then be exactly those specified. The
72 in the argument list is not relevant.
74 \fB-R\fR \fIroot-dir\fR | \fB--chroot\fR \fIroot-dir\fR
75 The program will have its root directory set to
78 .BR "Do not use this option unless you know what you are doing" :
79 Unlike chroot(8), the current working directory will remain unchanged.
80 This means that if the current directory isn't underneath the
81 specified new root, the program will still be able to access files
82 outside the new root by using relative pathnames. If this isn't
83 what you want, please use the chroot utility instead.
86 Indicates the end of the options. The next argument (if present) will
87 be interpreted as the command name, even if it starts with a hyphen.
88 .SH SECURITY CONSIDERATIONS
90 is designed so that installing it setuid root is extremely unlikely to
91 compromise the security of any system. It will check using
93 whether the real user is allowed to write to
95 and if this check fails
97 will exit without even attempting to parse its command line.
102 designed to be resistant to malicious command line arguments. Do not
103 allow untrusted processes to pass options to really, or to specify the
104 command to be run. Whether it is safe to allow relatively untrusted
105 processes to pass options to the command which is to be run depends on
106 the behaviour of that command and its security status.
110 to drop privilege is dangerous unless the calling environment is very
111 well understood. There are many inherited process properties and
112 resources which might be used by the callee to escalate its privilege
113 to that of the (root-equivalent) caller. For this function, it is
114 usually better to use
119 does not manipulate the environment at all. The calling program is
120 run in exactly the same environment as the caller passes to
130 accounts will usually need to have these directories on their
136 is used to find the default shell to use in interactive mode (ie, when
137 no command is specified).
141 was written by Ian Jackson <ian@chiark.greenend.org.uk>.
143 It and this manpage are Copyright (C) 1992-5,2004,2013 Ian Jackson
144 <ian@chiark.greenend.org.uk>.
147 is free software; you can redistribute it and/or modify
148 it under the terms of the GNU General Public License as
149 published by the Free Software Foundation; either version 3,
150 or (at your option) any later version.
153 is distributed in the hope that it will be useful, but
154 WITHOUT ANY WARRANTY; without even the implied warranty of
155 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
156 GNU General Public License for more details.
158 You should have received a copy of the GNU General Public
159 License along with this file; if not, consult the Free Software
160 Foundation's website at www.fsf.org, or the GNU Project website at
166 and is available for download from
167 ftp.chiark.greenend.org.uk in /users/ian/chiark-utils/,
168 in source and pre-compiled binary form, and also from Ian Jackson's